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Message-ID: <CAKfTPtBQnTJQaU6iYCz3JhZ0Y=MjyM7oZ3Ug_SNfyZ0AwVPXJQ@mail.gmail.com>
Date: Tue, 9 Jul 2024 09:48:06 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Qais Yousef <qyousef@...alina.io>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Viresh Kumar <viresh.kumar@...aro.org>,
Ingo Molnar <mingo@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>, Steven Rostedt <rostedt@...dmis.org>,
Dietmar Eggemann <dietmar.eggemann@....com>, Ben Segall <bsegall@...gle.com>,
Mel Gorman <mgorman@...e.de>, Daniel Bristot de Oliveira <bristot@...hat.com>,
Valentin Schneider <vschneid@...hat.com>, Christian Loehle <christian.loehle@....com>,
Hongyan Xia <hongyan.xia2@....com>, John Stultz <jstultz@...gle.com>, linux-pm@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6] sched: Consolidate cpufreq updates
On Wed, 19 Jun 2024 at 22:14, Qais Yousef <qyousef@...alina.io> wrote:
>
> Improve the interaction with cpufreq governors by making the
> cpufreq_update_util() calls more intentional.
>
> At the moment we send them when load is updated for CFS, bandwidth for
> DL and at enqueue/dequeue for RT. But this can lead to too many updates
> sent in a short period of time and potentially be ignored at a critical
> moment due to the rate_limit_us in schedutil.
>
> For example, simultaneous task enqueue on the CPU where 2nd task is
> bigger and requires higher freq. The trigger to cpufreq_update_util() by
> the first task will lead to dropping the 2nd request until tick. Or
> another CPU in the same policy triggers a freq update shortly after.
>
> Updates at enqueue for RT are not strictly required. Though they do help
> to reduce the delay for switching the frequency and the potential
> observation of lower frequency during this delay. But current logic
> doesn't intentionally (at least to my understanding) try to speed up the
> request.
>
> To help reduce the amount of cpufreq updates and make them more
> purposeful, consolidate them into these locations:
>
> 1. context_switch()
> 2. task_tick_fair()
> 3. update_blocked_averages()
> 4. on syscall that changes policy or uclamp values
> 5. on check_preempt_wakeup_fair() if wakeup preemption failed
So this above is the new thing to take care of enqueues that generate
sudden updates of util_est and could require a frequency change, isn't
it ?
>
> The update at context switch should help guarantee that DL and RT get
> the right frequency straightaway when they're RUNNING. As mentioned
> though the update will happen slightly after enqueue_task(); though in
> an ideal world these tasks should be RUNNING ASAP and this additional
That's probably ok for RT although it means possibly running up to the
switch at lowest frequency but I suppose it's not a big concern as it
is already the case if the RT task will end up on a different CPU than
the local one.
I'm more concerned about DL tasks. cpu_bw_dl() reflects the min
bandwidth/capacity to run all enqueued DL tasks in time. The dl
bandwidth is updated when a DL task is enqueued and this
bandwidth/capacity should be applied immediately and not at the next
context switch otherwise you will not have enough bandwidth if the
newly enqueued DL task does not preempt current DL task
> delay should be negligible. For fair tasks we need to make sure we send
> a single update for every decay for the root cfs_rq. Any changes to the
> rq will be deferred until the next task is ready to run, or we hit TICK.
> But we are guaranteed the task is running at a level that meets its
> requirements after enqueue.
>
> To guarantee RT and DL tasks updates are never missed, we add a new
> SCHED_CPUFREQ_FORCE_UPDATE to ignore the rate_limit_us. If we are
> already running at the right freq, the governor will end up doing
> nothing, but we eliminate the risk of the task ending up accidentally
> running at the wrong freq due to rate_limit_us.
>
> Similarly for iowait boost, we ignore rate limits. We also handle a case
> of a boost reset prematurely by adding a guard in sugov_iowait_apply()
> to reduce the boost after 1ms which seems iowait boost mechanism relied
> on rate_limit_us and cfs_rq.decay preventing any updates to happen soon
> after iowait boost.
>
> The new SCHED_CPUFREQ_FORCE_UPDATE should not impact the rate limit
> time stamps otherwise we can end up delaying updates for normal
> requests.
>
> As a simple optimization, we avoid sending cpufreq updates when
> switching from RT to another RT as RT tasks run at max freq by default.
> If CONFIG_UCLAMP_TASK is enabled, we can do a simple check to see if
> uclamp_min is different to avoid unnecessary cpufreq update as most RT
> tasks are likely to be running at the same performance level, so we can
> avoid unnecessary overhead of forced updates when there's nothing to do.
>
> We also ensure to ignore cpufreq udpates for sugov workers at context
> switch. It doesn't make sense for the kworker that applies the frequency
> update (which is a DL task) to trigger a frequency update itself.
>
> The update at task_tick_fair will guarantee that the governor will
> follow any updates to load for tasks/CPU or due to new enqueues/dequeues
> to the rq. Since DL and RT always run at constant frequencies and have
> no load tracking, this is only required for fair tasks.
>
> The update at update_blocked_averages() will ensure we decay frequency
> as the CPU becomes idle for long enough.
>
> If the currently running task changes its policy or uclamp values, we
> ensure we follow up with cpufreq update to ensure we follow up with any
> potential new perf requirements based on the new change.
>
> To handle systems with long TICK where tasks could end up enqueued but
> no preemption happens until TICK, we add an update in
> check_preempt_wakeup_fair() if wake up preemption fails. This will send
> special SCHED_CPUFREQ_TASK_ENQUEUED cpufreq update to tell the governor
> that the state of the CPU has changed and it can consider an update if
> it deems worthwhile. In schedutil this will do an update if no update
> was done since sysctl_sched_base_slice which is our ideal slice length
> for context switch.
>
> Since we now DL tasks always ignore rate limit, remove
> ignore_dl_rate_limit() function as it's no longer necessary.
>
> Also move updating sg_cpu->last_update inside sugov_iowait_boost() where
> this variable is associated.
>
> Results of
>
> taskset 1 perf stat --repeat 10 -e cycles,instructions,task-clock perf bench sched pipe
>
> on AMD 3900X to verify any potential overhead because of the addition at
> context switch against v6.8.7 stable kernel
>
> v6.8.7: schedutil:
> ------------------
>
> Performance counter stats for 'perf bench sched pipe' (10 runs):
>
> 814,886,355 cycles:u # 0.073 GHz ( +- 1.79% )
> 82,724,139 instructions:u # 0.10 insn per cycle ( +- 0.00% )
> 11,112.19 msec task-clock:u # 0.996 CPUs utilized ( +- 0.18% )
>
> 11.1575 +- 0.0207 seconds time elapsed ( +- 0.19% )
>
> v6.8.7: performance:
> --------------------
>
> Performance counter stats for 'perf bench sched pipe' (10 runs):
>
> 731,701,038 cycles:u # 0.067 GHz ( +- 2.27% )
> 82,724,255 instructions:u # 0.10 insn per cycle ( +- 0.00% )
> 10,830.95 msec task-clock:u # 0.992 CPUs utilized ( +- 0.14% )
>
> 10.9172 +- 0.0150 seconds time elapsed ( +- 0.14% )
>
> v6.8.7+patch: schedutil:
> ------------------------
>
> Performance counter stats for 'perf bench sched pipe' (10 runs):
>
> 814,294,812 cycles:u # 0.073 GHz ( +- 1.45% )
> 82,724,229 instructions:u # 0.10 insn per cycle ( +- 0.00% )
> 11,109.70 msec task-clock:u # 1.000 CPUs utilized ( +- 0.11% )
>
> 11.1131 +- 0.0125 seconds time elapsed ( +- 0.11% )
>
> v6.8.7+patch: performance:
> --------------------------
>
> Performance counter stats for 'perf bench sched pipe' (10 runs):
>
> 849,621,311 cycles:u # 0.077 GHz ( +- 0.50% )
> 82,724,306 instructions:u # 0.10 insn per cycle ( +- 0.00% )
> 11,031.10 msec task-clock:u # 0.996 CPUs utilized ( +- 0.14% )
>
> 11.0716 +- 0.0149 seconds time elapsed ( +- 0.13% )
>
> With performance governor we seem to be doing slightly worse. Comparing
> perf diff of
>
> taskset 1 perf record perf bench sched pipe
>
> 28.95% -3.66% [kernel.kallsyms] [k] delay_halt_mwaitx
> 1.49% +1.08% [kernel.kallsyms] [k] update_load_avg
> 1.14% +0.86% [kernel.kallsyms] [k] native_sched_clock
> 0.56% +0.56% [kernel.kallsyms] [k] sched_clock_cpu
> 7.34% -0.45% [kernel.kallsyms] [k] native_write_msr
> 8.54% -0.42% [kernel.kallsyms] [k] native_read_msr
> 1.07% +0.34% [kernel.kallsyms] [k] pick_next_task_fair
> 2.46% -0.30% [kernel.kallsyms] [k] x86_pmu_disable_all
> 1.73% -0.28% [kernel.kallsyms] [k] amd_pmu_check_overflow
> 0.36% +0.27% [kernel.kallsyms] [k] sched_clock
> 1.05% -0.25% [kernel.kallsyms] [k] try_to_wake_up
> 0.70% -0.24% [kernel.kallsyms] [k] enqueue_task_fair
> 0.88% +0.20% [kernel.kallsyms] [k] pipe_read
> 0.54% +0.19% [kernel.kallsyms] [k] dequeue_entity
> 0.37% +0.17% [kernel.kallsyms] [k] aa_file_perm
> 0.66% +0.16% [kernel.kallsyms] [k] vfs_write
> 0.11% +0.15% [kernel.kallsyms] [k] __x64_sys_write
> 0.35% +0.15% libc.so.6 [.] __GI___libc_write
> 1.32% +0.15% [kernel.kallsyms] [k] update_curr
> 1.22% +0.14% [kernel.kallsyms] [k] psi_task_switch
> 0.58% -0.14% [kernel.kallsyms] [k] enqueue_entity
> 0.83% +0.14% perf [.] worker_thread
> 0.63% +0.13% [kernel.kallsyms] [k] dequeue_task_fair
> 1.42% -0.13% [kernel.kallsyms] [k] delay_halt
> 0.24% +0.13% [kernel.kallsyms] [k] __wake_up_common
>
> It seems update_load_avg() is slightly worse. Earlier versions of the
> patch didn't produce such a difference. I am not sure if this is
> a problem or just attributed to minor binary difference and caching
> effect.
>
> Note worthy that we still have the following race condition on systems
> that have shared policy:
>
> * CPUs with shared policy can end up sending simultaneous cpufreq
> updates requests where the 2nd one will be unlucky and get blocked by
> the rate_limit_us (schedutil).
>
> We can potentially address this limitation later, but it is out of the
> scope of this patch.
>
> Signed-off-by: Qais Yousef <qyousef@...alina.io>
> ---
>
> Changes since v5:
>
> * Fix a bug where switching between RT and sugov tasks triggered an
> endless cycle of cpufreq updates.
> * Only do cpufreq updates at tick for fair after verifying
> rq->cfs.decayed
> * Remove optimization in update_load_avg() to avoid sending an update
> if util hasn't changed that caused a bug when switching from Idle
> * Handle systems with long ticks by adding extra update on
> check_preempt_wakeup_fair(). The idea is to rely on context switch
> but still consider an update if wakeup preemption failed and no
> update was sent since sysctl_sched_base_slice
> * Remove ignore_dl_rate_limit() as this function is now redundant
> * move sg_cpu->last_update = time inside sugov_iowait_boost()
> * Update commit message with new details and with perf diff output
>
> Changes since v4:
>
> * Fix updating freq when uclamp changes before the dequeue/enqueue
> dance. (Hongyan)
> * Rebased on top of tip/sched/core 6.10-rc1 and resolve some conflicts
> due to code shuffling to syscalls.c. Added new function
> update_cpufreq_current() to be used outside core.c when
> task_current() requires cpufreq update.
>
> Changes since v3:
>
> * Omit cpufreq updates at attach/detach_entity_load_avg(). They share
> the update path from enqueue/dequeue which is not intended to trigger
> an update. And task_change_group_fair() is not expected to cause the
> root cfs_rq util to change significantly to warrant an immediate
> update for enqueued tasks. Better defer for next context switch to
> sample the state of the cpu taking all changes into account before
> the next task is due to run.
> Dietmar also pointed out a bug where we could send more updates vs
> without the patch in this path as I wasn't sending the update for
> cfs_rq == &rq->cfs.
>
> Changes since v2:
>
> * Clean up update_cpufreq_ctx_switch() to reduce branches (Peter)
> * Fix issue with cpufreq updates missed on switching from idle (Vincent)
> * perf bench sched pipe regressed after fixing the switch from idle,
> detect when util_avg has changed when cfs_rq->decayed to fix it
> * Ensure to issue cpufreq updates when task_current() switches
> policy/uclamp values
>
> Changes since v1:
>
> * Use taskset and measure with performance governor as Ingo suggested
> * Remove the static key as I found out we always register a function
> for cpu_dbs in cpufreq_governor.c; and as Christian pointed out it
> trigger a lock debug warning.
> * Improve detection of sugov workers by using SCHED_FLAG_SUGOV
> * Guard against NSEC_PER_MSEC instead of TICK_USEC to avoid prematurely
> reducing iowait boost as the latter was a NOP and like
> sugov_iowait_reset() like Christian pointed out.
>
> v1 discussion: https://lore.kernel.org/all/20240324020139.1032473-1-qyousef@layalina.io/
> v2 discussion: https://lore.kernel.org/lkml/20240505233103.168766-1-qyousef@layalina.io/
> v3 discussion: https://lore.kernel.org/lkml/20240512190018.531820-1-qyousef@layalina.io/
> v4 discussion: https://lore.kernel.org/lkml/20240516204802.846520-1-qyousef@layalina.io/
> v5 discussion: https://lore.kernel.org/lkml/20240530104653.1234004-1-qyousef@layalina.io/
>
> include/linux/sched/cpufreq.h | 4 +-
> kernel/sched/core.c | 107 +++++++++++++++++++++++++++--
> kernel/sched/cpufreq_schedutil.c | 111 ++++++++++++++++++++-----------
> kernel/sched/deadline.c | 4 --
> kernel/sched/fair.c | 79 ++++++++--------------
> kernel/sched/rt.c | 8 +--
> kernel/sched/sched.h | 9 ++-
> kernel/sched/syscalls.c | 26 ++++++--
> 8 files changed, 232 insertions(+), 116 deletions(-)
>
> diff --git a/include/linux/sched/cpufreq.h b/include/linux/sched/cpufreq.h
> index bdd31ab93bc5..5409a9f79cc0 100644
> --- a/include/linux/sched/cpufreq.h
> +++ b/include/linux/sched/cpufreq.h
> @@ -8,7 +8,9 @@
> * Interface between cpufreq drivers and the scheduler:
> */
>
> -#define SCHED_CPUFREQ_IOWAIT (1U << 0)
> +#define SCHED_CPUFREQ_IOWAIT (1U << 0)
> +#define SCHED_CPUFREQ_FORCE_UPDATE (1U << 1) /* ignore transition_delay_us */
> +#define SCHED_CPUFREQ_TASK_ENQUEUED (1U << 2) /* new fair task was enqueued */
>
> #ifdef CONFIG_CPU_FREQ
> struct cpufreq_policy;
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 0935f9d4bb7b..732acf9cc0c5 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -153,6 +153,9 @@ const_debug unsigned int sysctl_sched_nr_migrate = SCHED_NR_MIGRATE_BREAK;
>
> __read_mostly int scheduler_running;
>
> +static __always_inline void
> +__update_cpufreq_ctx_switch(struct rq *rq, struct task_struct *prev);
> +
> #ifdef CONFIG_SCHED_CORE
>
> DEFINE_STATIC_KEY_FALSE(__sched_core_enabled);
> @@ -2042,17 +2045,24 @@ inline int task_curr(const struct task_struct *p)
> * this means any call to check_class_changed() must be followed by a call to
> * balance_callback().
> */
> -void check_class_changed(struct rq *rq, struct task_struct *p,
> +bool check_class_changed(struct rq *rq, struct task_struct *p,
> const struct sched_class *prev_class,
> int oldprio)
> {
> + bool class_changed = false;
> +
> if (prev_class != p->sched_class) {
> if (prev_class->switched_from)
> prev_class->switched_from(rq, p);
>
> p->sched_class->switched_to(rq, p);
> - } else if (oldprio != p->prio || dl_task(p))
> +
> + class_changed = true;
> + } else if (oldprio != p->prio || dl_task(p)) {
> p->sched_class->prio_changed(rq, p, oldprio);
> + }
> +
> + return class_changed;
> }
>
> void wakeup_preempt(struct rq *rq, struct task_struct *p, int flags)
> @@ -4917,6 +4927,84 @@ static inline void __balance_callbacks(struct rq *rq)
>
> #endif
>
> +static __always_inline void
> +__update_cpufreq_ctx_switch(struct rq *rq, struct task_struct *prev)
> +{
> +#ifdef CONFIG_CPU_FREQ
> + if (prev && prev->dl.flags & SCHED_FLAG_SUGOV) {
> + /* Sugov just did an update, don't be too aggressive */
> + return;
> + }
> +
> + /*
> + * RT and DL should always send a freq update. But we can do some
> + * simple checks to avoid it when we know it's not necessary.
> + *
> + * iowait_boost will always trigger a freq update too.
> + *
> + * Fair tasks will only trigger an update if the root cfs_rq has
> + * decayed.
> + *
> + * Everything else should do nothing.
> + */
> + switch (current->policy) {
> + case SCHED_NORMAL:
> + case SCHED_BATCH:
> + if (unlikely(current->in_iowait)) {
> + cpufreq_update_util(rq, SCHED_CPUFREQ_IOWAIT | SCHED_CPUFREQ_FORCE_UPDATE);
> + return;
> + }
> +
> +#ifdef CONFIG_SMP
> + if (unlikely(rq->cfs.decayed)) {
> + rq->cfs.decayed = false;
> + cpufreq_update_util(rq, 0);
> + return;
> + }
> +#else
> + cpufreq_update_util(rq, 0);
> +#endif
> + return;
> + case SCHED_FIFO:
> + case SCHED_RR:
> + if (prev && rt_policy(prev->policy)) {
> +#ifdef CONFIG_UCLAMP_TASK
> + unsigned long curr_uclamp_min = uclamp_eff_value(current, UCLAMP_MIN);
> + unsigned long prev_uclamp_min = uclamp_eff_value(prev, UCLAMP_MIN);
> +
> + if (curr_uclamp_min == prev_uclamp_min)
> +#endif
> + return;
> + }
> +#ifdef CONFIG_SMP
> + /* Stopper task masquerades as RT */
> + if (unlikely(current->sched_class == &stop_sched_class))
> + return;
> +#endif
> + cpufreq_update_util(rq, SCHED_CPUFREQ_FORCE_UPDATE);
> + return;
> + case SCHED_DEADLINE:
> + if (current->dl.flags & SCHED_FLAG_SUGOV) {
> + /* Ignore sugov kthreads, they're responding to our requests */
> + return;
> + }
> + cpufreq_update_util(rq, SCHED_CPUFREQ_FORCE_UPDATE);
> + return;
> + default:
> + return;
> + }
> +#endif
> +}
> +
> +/*
> + * Call when currently running task had an attribute change that requires
> + * an immediate cpufreq update.
> + */
> +void update_cpufreq_current(struct rq *rq)
> +{
> + __update_cpufreq_ctx_switch(rq, NULL);
> +}
> +
> static inline void
> prepare_lock_switch(struct rq *rq, struct task_struct *next, struct rq_flags *rf)
> {
> @@ -4934,7 +5022,7 @@ prepare_lock_switch(struct rq *rq, struct task_struct *next, struct rq_flags *rf
> #endif
> }
>
> -static inline void finish_lock_switch(struct rq *rq)
> +static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev)
> {
> /*
> * If we are tracking spinlock dependencies then we have to
> @@ -4943,6 +5031,11 @@ static inline void finish_lock_switch(struct rq *rq)
> */
> spin_acquire(&__rq_lockp(rq)->dep_map, 0, 0, _THIS_IP_);
> __balance_callbacks(rq);
> + /*
> + * Request freq update after __balance_callbacks to take into account
> + * any changes to rq.
> + */
> + __update_cpufreq_ctx_switch(rq, prev);
> raw_spin_rq_unlock_irq(rq);
> }
>
> @@ -5061,7 +5154,7 @@ static struct rq *finish_task_switch(struct task_struct *prev)
> perf_event_task_sched_in(prev, current);
> finish_task(prev);
> tick_nohz_task_switch();
> - finish_lock_switch(rq);
> + finish_lock_switch(rq, prev);
> finish_arch_post_lock_switch();
> kcov_finish_switch(current);
> /*
> @@ -6920,6 +7013,7 @@ void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task)
> int prio, oldprio, queued, running, queue_flag =
> DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
> const struct sched_class *prev_class;
> + bool class_changed;
> struct rq_flags rf;
> struct rq *rq;
>
> @@ -7021,7 +7115,10 @@ void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task)
> if (running)
> set_next_task(rq, p);
>
> - check_class_changed(rq, p, prev_class, oldprio);
> + class_changed = check_class_changed(rq, p, prev_class, oldprio);
> + if (class_changed && running)
> + update_cpufreq_current(rq);
> +
> out_unlock:
> /* Avoid rq from going away on us: */
> preempt_disable();
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index eece6244f9d2..4cdaca0a984e 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -59,10 +59,32 @@ static DEFINE_PER_CPU(struct sugov_cpu, sugov_cpu);
>
> /************************ Governor internals ***********************/
>
> -static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time)
> +static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time,
> + unsigned int flags)
> {
> s64 delta_ns;
>
> + delta_ns = time - sg_policy->last_freq_update_time;
> +
> + /*
> + * We want to update cpufreq at context switch, but on systems with
> + * long TICK values, this can happen after a long time while more tasks
> + * would have been added meanwhile leaving us potentially running at
> + * inadequate frequency for extended period of time.
> + *
> + * This logic should only apply when new fair task was added to the
> + * CPU, we'd want to defer to context switch as much as possible, but
> + * to avoid the potential delays mentioned above, let's check if this
> + * additional tasks warrants sending an update sooner.
> + *
> + * We want to ensure there's at least an update every
> + * sysctl_sched_base_slice.
> + */
> + if (likely(flags & SCHED_CPUFREQ_TASK_ENQUEUED)) {
> + if (delta_ns < sysctl_sched_base_slice)
I'm not sure that this is the right condition. This value seems quite
long to me and not that much different from a 4ms tick. Should we use
the 1024us of the pelt
Also, I run the use case that I ran previously and I have cases where
we wait more than 4.5 ms between the enqueue of the big task and the
freq update (with a 1ms tick period) so There are probably some corner
cases which are not correctly handled.
My use case is 2 tasks running on the same cpu. 1 short task A running
500us with a period of 19457us and 1 long task B running 19000 us with
a period of 139777us. The periods are set to never be in sync with the
tick which is 1 ms. There are cases when task B wakes up while task A
is already running and doesn't preempt A and the freq update happens
only 4.5ms after task B wakes up and task A went back to sleep whereas
we should switch immediatly from 760Mhz to 1958 Mhz
> + return false;
> + }
> +
> /*
> * Since cpufreq_update_util() is called with rq->lock held for
> * the @target_cpu, our per-CPU data is fully serialized.
> @@ -87,13 +109,14 @@ static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time)
> return true;
> }
>
> - delta_ns = time - sg_policy->last_freq_update_time;
> + if (unlikely(flags & SCHED_CPUFREQ_FORCE_UPDATE))
> + return true;
>
> return delta_ns >= sg_policy->freq_update_delay_ns;
> }
>
> static bool sugov_update_next_freq(struct sugov_policy *sg_policy, u64 time,
> - unsigned int next_freq)
> + unsigned int next_freq, unsigned int flags)
> {
> if (sg_policy->need_freq_update)
> sg_policy->need_freq_update = cpufreq_driver_test_flags(CPUFREQ_NEED_UPDATE_LIMITS);
> @@ -101,7 +124,9 @@ static bool sugov_update_next_freq(struct sugov_policy *sg_policy, u64 time,
> return false;
>
> sg_policy->next_freq = next_freq;
> - sg_policy->last_freq_update_time = time;
> +
> + if (!unlikely(flags & SCHED_CPUFREQ_FORCE_UPDATE))
> + sg_policy->last_freq_update_time = time;
>
> return true;
> }
> @@ -249,9 +274,12 @@ static void sugov_iowait_boost(struct sugov_cpu *sg_cpu, u64 time,
> unsigned int flags)
> {
> bool set_iowait_boost = flags & SCHED_CPUFREQ_IOWAIT;
> + bool forced_update = flags & SCHED_CPUFREQ_FORCE_UPDATE;
> +
> + sg_cpu->last_update = time;
>
> /* Reset boost if the CPU appears to have been idle enough */
> - if (sg_cpu->iowait_boost &&
> + if (sg_cpu->iowait_boost && !forced_update &&
> sugov_iowait_reset(sg_cpu, time, set_iowait_boost))
> return;
>
> @@ -294,17 +322,34 @@ static void sugov_iowait_boost(struct sugov_cpu *sg_cpu, u64 time,
> * being more conservative on tasks which does sporadic IO operations.
> */
> static unsigned long sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time,
> - unsigned long max_cap)
> + unsigned long max_cap, unsigned int flags)
> {
> + bool forced_update = flags & SCHED_CPUFREQ_FORCE_UPDATE;
> + s64 delta_ns = time - sg_cpu->last_update;
> +
> /* No boost currently required */
> if (!sg_cpu->iowait_boost)
> return 0;
>
> + if (forced_update)
> + goto apply_boost;
> +
> /* Reset boost if the CPU appears to have been idle enough */
> if (sugov_iowait_reset(sg_cpu, time, false))
> return 0;
>
> if (!sg_cpu->iowait_boost_pending) {
> + /*
> + * This logic relied on PELT signal decays happening once every
> + * 1ms. But due to changes to how updates are done now, we can
> + * end up with more request coming up leading to iowait boost
> + * to be prematurely reduced. Make the assumption explicit
> + * until we improve the iowait boost logic to be better in
> + * general as it is due for an overhaul.
> + */
> + if (delta_ns <= NSEC_PER_MSEC)
> + goto apply_boost;
> +
> /*
> * No boost pending; reduce the boost value.
> */
> @@ -315,6 +360,7 @@ static unsigned long sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time,
> }
> }
>
> +apply_boost:
> sg_cpu->iowait_boost_pending = false;
>
> /*
> @@ -337,31 +383,18 @@ static bool sugov_cpu_is_busy(struct sugov_cpu *sg_cpu)
> static inline bool sugov_cpu_is_busy(struct sugov_cpu *sg_cpu) { return false; }
> #endif /* CONFIG_NO_HZ_COMMON */
>
> -/*
> - * Make sugov_should_update_freq() ignore the rate limit when DL
> - * has increased the utilization.
> - */
> -static inline void ignore_dl_rate_limit(struct sugov_cpu *sg_cpu)
> -{
> - if (cpu_bw_dl(cpu_rq(sg_cpu->cpu)) > sg_cpu->bw_min)
> - sg_cpu->sg_policy->limits_changed = true;
> -}
> -
> static inline bool sugov_update_single_common(struct sugov_cpu *sg_cpu,
> u64 time, unsigned long max_cap,
> unsigned int flags)
> {
> unsigned long boost;
>
> - sugov_iowait_boost(sg_cpu, time, flags);
> - sg_cpu->last_update = time;
> -
> - ignore_dl_rate_limit(sg_cpu);
> -
> - if (!sugov_should_update_freq(sg_cpu->sg_policy, time))
> + if (!sugov_should_update_freq(sg_cpu->sg_policy, time, flags))
> return false;
>
> - boost = sugov_iowait_apply(sg_cpu, time, max_cap);
> + sugov_iowait_boost(sg_cpu, time, flags);
> +
> + boost = sugov_iowait_apply(sg_cpu, time, max_cap, flags);
> sugov_get_util(sg_cpu, boost);
>
> return true;
> @@ -397,7 +430,7 @@ static void sugov_update_single_freq(struct update_util_data *hook, u64 time,
> sg_policy->cached_raw_freq = cached_freq;
> }
>
> - if (!sugov_update_next_freq(sg_policy, time, next_f))
> + if (!sugov_update_next_freq(sg_policy, time, next_f, flags))
> return;
>
> /*
> @@ -449,10 +482,12 @@ static void sugov_update_single_perf(struct update_util_data *hook, u64 time,
> cpufreq_driver_adjust_perf(sg_cpu->cpu, sg_cpu->bw_min,
> sg_cpu->util, max_cap);
>
> - sg_cpu->sg_policy->last_freq_update_time = time;
> + if (!unlikely(flags & SCHED_CPUFREQ_FORCE_UPDATE))
> + sg_cpu->sg_policy->last_freq_update_time = time;
> }
>
> -static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time)
> +static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time,
> + unsigned int flags)
> {
> struct sugov_policy *sg_policy = sg_cpu->sg_policy;
> struct cpufreq_policy *policy = sg_policy->policy;
> @@ -465,7 +500,7 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time)
> struct sugov_cpu *j_sg_cpu = &per_cpu(sugov_cpu, j);
> unsigned long boost;
>
> - boost = sugov_iowait_apply(j_sg_cpu, time, max_cap);
> + boost = sugov_iowait_apply(j_sg_cpu, time, max_cap, flags);
> sugov_get_util(j_sg_cpu, boost);
>
> util = max(j_sg_cpu->util, util);
> @@ -483,22 +518,20 @@ sugov_update_shared(struct update_util_data *hook, u64 time, unsigned int flags)
>
> raw_spin_lock(&sg_policy->update_lock);
>
> - sugov_iowait_boost(sg_cpu, time, flags);
> - sg_cpu->last_update = time;
> + if (!sugov_should_update_freq(sg_policy, time, flags))
> + goto unlock;
>
> - ignore_dl_rate_limit(sg_cpu);
> + sugov_iowait_boost(sg_cpu, time, flags);
>
> - if (sugov_should_update_freq(sg_policy, time)) {
> - next_f = sugov_next_freq_shared(sg_cpu, time);
> + next_f = sugov_next_freq_shared(sg_cpu, time, flags);
>
> - if (!sugov_update_next_freq(sg_policy, time, next_f))
> - goto unlock;
> + if (!sugov_update_next_freq(sg_policy, time, next_f, flags))
> + goto unlock;
>
> - if (sg_policy->policy->fast_switch_enabled)
> - cpufreq_driver_fast_switch(sg_policy->policy, next_f);
> - else
> - sugov_deferred_update(sg_policy);
> - }
> + if (sg_policy->policy->fast_switch_enabled)
> + cpufreq_driver_fast_switch(sg_policy->policy, next_f);
> + else
> + sugov_deferred_update(sg_policy);
> unlock:
> raw_spin_unlock(&sg_policy->update_lock);
> }
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index b216e6deeac4..8e015e219da8 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -251,8 +251,6 @@ void __add_running_bw(u64 dl_bw, struct dl_rq *dl_rq)
> dl_rq->running_bw += dl_bw;
> SCHED_WARN_ON(dl_rq->running_bw < old); /* overflow */
> SCHED_WARN_ON(dl_rq->running_bw > dl_rq->this_bw);
> - /* kick cpufreq (see the comment in kernel/sched/sched.h). */
> - cpufreq_update_util(rq_of_dl_rq(dl_rq), 0);
> }
>
> static inline
> @@ -265,8 +263,6 @@ void __sub_running_bw(u64 dl_bw, struct dl_rq *dl_rq)
> SCHED_WARN_ON(dl_rq->running_bw > old); /* underflow */
> if (dl_rq->running_bw > old)
> dl_rq->running_bw = 0;
> - /* kick cpufreq (see the comment in kernel/sched/sched.h). */
> - cpufreq_update_util(rq_of_dl_rq(dl_rq), 0);
> }
>
> static inline
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 41b58387023d..bb67888486c3 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3988,29 +3988,6 @@ static inline void update_cfs_group(struct sched_entity *se)
> }
> #endif /* CONFIG_FAIR_GROUP_SCHED */
>
> -static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq, int flags)
> -{
> - struct rq *rq = rq_of(cfs_rq);
> -
> - if (&rq->cfs == cfs_rq) {
> - /*
> - * There are a few boundary cases this might miss but it should
> - * get called often enough that that should (hopefully) not be
> - * a real problem.
> - *
> - * It will not get called when we go idle, because the idle
> - * thread is a different class (!fair), nor will the utilization
> - * number include things like RT tasks.
> - *
> - * As is, the util number is not freq-invariant (we'd have to
> - * implement arch_scale_freq_capacity() for that).
> - *
> - * See cpu_util_cfs().
> - */
> - cpufreq_update_util(rq, flags);
> - }
> -}
> -
> #ifdef CONFIG_SMP
> static inline bool load_avg_is_decayed(struct sched_avg *sa)
> {
> @@ -4688,8 +4665,6 @@ static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
>
> add_tg_cfs_propagate(cfs_rq, se->avg.load_sum);
>
> - cfs_rq_util_change(cfs_rq, 0);
> -
> trace_pelt_cfs_tp(cfs_rq);
> }
>
> @@ -4718,8 +4693,6 @@ static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
>
> add_tg_cfs_propagate(cfs_rq, -se->avg.load_sum);
>
> - cfs_rq_util_change(cfs_rq, 0);
> -
> trace_pelt_cfs_tp(cfs_rq);
> }
>
> @@ -4735,7 +4708,6 @@ static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
> static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
> {
> u64 now = cfs_rq_clock_pelt(cfs_rq);
> - int decayed;
>
> /*
> * Track task load average for carrying it to new CPU after migrated, and
> @@ -4744,8 +4716,8 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
> if (se->avg.last_update_time && !(flags & SKIP_AGE_LOAD))
> __update_load_avg_se(now, cfs_rq, se);
>
> - decayed = update_cfs_rq_load_avg(now, cfs_rq);
> - decayed |= propagate_entity_load_avg(se);
> + cfs_rq->decayed |= update_cfs_rq_load_avg(now, cfs_rq);
> + cfs_rq->decayed |= propagate_entity_load_avg(se);
>
> if (!se->avg.last_update_time && (flags & DO_ATTACH)) {
>
> @@ -4766,11 +4738,8 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
> */
> detach_entity_load_avg(cfs_rq, se);
> update_tg_load_avg(cfs_rq);
> - } else if (decayed) {
> - cfs_rq_util_change(cfs_rq, 0);
> -
> - if (flags & UPDATE_TG)
> - update_tg_load_avg(cfs_rq);
> + } else if (cfs_rq->decayed && (flags & UPDATE_TG)) {
> + update_tg_load_avg(cfs_rq);
> }
> }
>
> @@ -5145,7 +5114,6 @@ static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
>
> static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int not_used1)
> {
> - cfs_rq_util_change(cfs_rq, 0);
> }
>
> static inline void remove_entity_load_avg(struct sched_entity *se) {}
> @@ -6760,14 +6728,6 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
> */
> util_est_enqueue(&rq->cfs, p);
>
> - /*
> - * If in_iowait is set, the code below may not trigger any cpufreq
> - * utilization updates, so do it here explicitly with the IOWAIT flag
> - * passed.
> - */
> - if (p->in_iowait)
> - cpufreq_update_util(rq, SCHED_CPUFREQ_IOWAIT);
> -
> for_each_sched_entity(se) {
> if (se->on_rq)
> break;
> @@ -8354,7 +8314,7 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
> int cse_is_idle, pse_is_idle;
>
> if (unlikely(se == pse))
> - return;
> + goto nopreempt;
>
> /*
> * This is possible from callers such as attach_tasks(), in which we
> @@ -8363,7 +8323,7 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
> * next-buddy nomination below.
> */
> if (unlikely(throttled_hierarchy(cfs_rq_of(pse))))
> - return;
> + goto nopreempt;
>
> if (sched_feat(NEXT_BUDDY) && !(wake_flags & WF_FORK)) {
> set_next_buddy(pse);
> @@ -8380,7 +8340,7 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
> * below.
> */
> if (test_tsk_need_resched(curr))
> - return;
> + goto nopreempt;
>
> /* Idle tasks are by definition preempted by non-idle tasks. */
> if (unlikely(task_has_idle_policy(curr)) &&
> @@ -8392,7 +8352,7 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
> * is driven by the tick):
> */
> if (unlikely(p->policy != SCHED_NORMAL) || !sched_feat(WAKEUP_PREEMPTION))
> - return;
> + goto nopreempt;
>
> find_matching_se(&se, &pse);
> WARN_ON_ONCE(!pse);
> @@ -8407,7 +8367,7 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
> if (cse_is_idle && !pse_is_idle)
> goto preempt;
> if (cse_is_idle != pse_is_idle)
> - return;
> + goto nopreempt;
>
> cfs_rq = cfs_rq_of(se);
> update_curr(cfs_rq);
> @@ -8418,6 +8378,14 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
> if (pick_eevdf(cfs_rq) == pse)
> goto preempt;
>
> +nopreempt:
> +#ifdef CONFIG_SMP
> + if (rq->cfs.decayed && rq->cfs.h_nr_running > 1)
> + cpufreq_update_util(rq, SCHED_CPUFREQ_TASK_ENQUEUED);
> +#else
> + if (rq->cfs.h_nr_running > 1)
> + cpufreq_update_util(rq, SCHED_CPUFREQ_TASK_ENQUEUED);
> +#endif
> return;
>
> preempt:
> @@ -9357,10 +9325,6 @@ static bool __update_blocked_others(struct rq *rq, bool *done)
> unsigned long hw_pressure;
> bool decayed;
>
> - /*
> - * update_load_avg() can call cpufreq_update_util(). Make sure that RT,
> - * DL and IRQ signals have been updated before updating CFS.
> - */
> curr_class = rq->curr->sched_class;
>
> hw_pressure = arch_scale_hw_pressure(cpu_of(rq));
> @@ -12699,6 +12663,15 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
> update_misfit_status(curr, rq);
> check_update_overutilized_status(task_rq(curr));
>
> +#ifdef CONFIG_SMP
> + if (rq->cfs.decayed) {
> + rq->cfs.decayed = false;
> + cpufreq_update_util(rq, 0);
> + }
> +#else
> + cpufreq_update_util(rq, 0);
> +#endif
> +
> task_tick_core(rq, curr);
> }
>
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 63e49c8ffc4d..92ed373e5b90 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -555,11 +555,8 @@ static void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
>
> rt_se = rt_rq->tg->rt_se[cpu];
>
> - if (!rt_se) {
> + if (!rt_se)
> dequeue_top_rt_rq(rt_rq, rt_rq->rt_nr_running);
> - /* Kick cpufreq (see the comment in kernel/sched/sched.h). */
> - cpufreq_update_util(rq_of_rt_rq(rt_rq), 0);
> - }
> else if (on_rt_rq(rt_se))
> dequeue_rt_entity(rt_se, 0);
> }
> @@ -1064,9 +1061,6 @@ enqueue_top_rt_rq(struct rt_rq *rt_rq)
> add_nr_running(rq, rt_rq->rt_nr_running);
> rt_rq->rt_queued = 1;
> }
> -
> - /* Kick cpufreq (see the comment in kernel/sched/sched.h). */
> - cpufreq_update_util(rq, 0);
> }
>
> #if defined CONFIG_SMP
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 62fd8bc6fd08..87325eff1884 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -639,6 +639,11 @@ struct cfs_rq {
> unsigned long runnable_avg;
> } removed;
>
> + /*
> + * Store whether last update_load_avg() has decayed
> + */
> + bool decayed;
> +
> #ifdef CONFIG_FAIR_GROUP_SCHED
> u64 last_update_tg_load_avg;
> unsigned long tg_load_avg_contrib;
> @@ -3608,10 +3613,12 @@ extern void set_load_weight(struct task_struct *p, bool update_load);
> extern void enqueue_task(struct rq *rq, struct task_struct *p, int flags);
> extern void dequeue_task(struct rq *rq, struct task_struct *p, int flags);
>
> -extern void check_class_changed(struct rq *rq, struct task_struct *p,
> +extern bool check_class_changed(struct rq *rq, struct task_struct *p,
> const struct sched_class *prev_class,
> int oldprio);
>
> +extern void update_cpufreq_current(struct rq *rq);
> +
> #ifdef CONFIG_SMP
> extern struct balance_callback *splice_balance_callbacks(struct rq *rq);
> extern void balance_callbacks(struct rq *rq, struct balance_callback *head);
> diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c
> index ae1b42775ef9..8b1194c39161 100644
> --- a/kernel/sched/syscalls.c
> +++ b/kernel/sched/syscalls.c
> @@ -491,7 +491,7 @@ static bool uclamp_reset(const struct sched_attr *attr,
> return false;
> }
>
> -static void __setscheduler_uclamp(struct task_struct *p,
> +static bool __setscheduler_uclamp(struct task_struct *p,
> const struct sched_attr *attr)
> {
> enum uclamp_id clamp_id;
> @@ -517,7 +517,7 @@ static void __setscheduler_uclamp(struct task_struct *p,
> }
>
> if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)))
> - return;
> + return false;
>
> if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN &&
> attr->sched_util_min != -1) {
> @@ -530,6 +530,8 @@ static void __setscheduler_uclamp(struct task_struct *p,
> uclamp_se_set(&p->uclamp_req[UCLAMP_MAX],
> attr->sched_util_max, true);
> }
> +
> + return true;
> }
>
> #else /* !CONFIG_UCLAMP_TASK: */
> @@ -539,8 +541,11 @@ static inline int uclamp_validate(struct task_struct *p,
> {
> return -EOPNOTSUPP;
> }
> -static void __setscheduler_uclamp(struct task_struct *p,
> - const struct sched_attr *attr) { }
> +static bool __setscheduler_uclamp(struct task_struct *p,
> + const struct sched_attr *attr)
> +{
> + return false;
> +}
> #endif
>
> /*
> @@ -614,6 +619,7 @@ int __sched_setscheduler(struct task_struct *p,
> int retval, oldprio, newprio, queued, running;
> const struct sched_class *prev_class;
> struct balance_callback *head;
> + bool update_cpufreq;
> struct rq_flags rf;
> int reset_on_fork;
> int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
> @@ -796,7 +802,8 @@ int __sched_setscheduler(struct task_struct *p,
> __setscheduler_params(p, attr);
> __setscheduler_prio(p, newprio);
> }
> - __setscheduler_uclamp(p, attr);
> +
> + update_cpufreq = __setscheduler_uclamp(p, attr);
>
> if (queued) {
> /*
> @@ -811,7 +818,14 @@ int __sched_setscheduler(struct task_struct *p,
> if (running)
> set_next_task(rq, p);
>
> - check_class_changed(rq, p, prev_class, oldprio);
> + update_cpufreq |= check_class_changed(rq, p, prev_class, oldprio);
> +
> + /*
> + * Changing class or uclamp value implies requiring to send cpufreq
> + * update.
> + */
> + if (update_cpufreq && running)
Why running ? it should be queued as we are max aggregating
> + update_cpufreq_current(rq);
>
> /* Avoid rq from going away on us: */
> preempt_disable();
> --
> 2.34.1
>
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