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Date: Wed, 18 Oct 2023 09:39:28 +0200
From: Beata Michalska <beata.michalska@....com>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
rafael@...nel.org, viresh.kumar@...aro.org, qyousef@...alina.io,
linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
lukasz.luba@....com
Subject: Re: [PATCH 2/2] sched/schedutil: rework iowait boost
On Fri, Oct 13, 2023 at 05:14:50PM +0200, Vincent Guittot wrote:
> Use the max value that has already been computed inside sugov_get_util()
> to cap the iowait boost and remove dependency with uclamp_rq_util_with()
> which is not used anymore.
>
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> ---
> kernel/sched/cpufreq_schedutil.c | 29 ++++++++-------
> kernel/sched/sched.h | 60 --------------------------------
> 2 files changed, 14 insertions(+), 75 deletions(-)
>
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 8cb323522b90..820612867769 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -177,11 +177,12 @@ unsigned long sugov_effective_cpu_perf(int cpu, unsigned long actual,
> return max(target, max);
> }
>
> -static void sugov_get_util(struct sugov_cpu *sg_cpu)
> +static void sugov_get_util(struct sugov_cpu *sg_cpu, unsigned long boost)
> {
> unsigned long min, max, util = cpu_util_cfs_boost(sg_cpu->cpu);
>
> util = effective_cpu_util(sg_cpu->cpu, util, &min, &max);
> + util = max(util, boost);
sugov_get_util could actually call sugov_iowait_apply here instead, to get a
centralized point of getting and applying the boost. Also sugov_iowait_apply
naming is no longer reflecting the functionality so maybe renaming it to smth
like sugov_iowait_get ?
---
BR
B.
> sg_cpu->bw_min = map_util_perf(min);
> sg_cpu->util = sugov_effective_cpu_perf(sg_cpu->cpu, util, min, max);
> }
> @@ -274,18 +275,16 @@ static void sugov_iowait_boost(struct sugov_cpu *sg_cpu, u64 time,
> * This mechanism is designed to boost high frequently IO waiting tasks, while
> * being more conservative on tasks which does sporadic IO operations.
> */
> -static void sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time,
> +static unsigned long sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time,
> unsigned long max_cap)
> {
> - unsigned long boost;
> -
> /* No boost currently required */
> if (!sg_cpu->iowait_boost)
> - return;
> + return 0;
>
> /* Reset boost if the CPU appears to have been idle enough */
> if (sugov_iowait_reset(sg_cpu, time, false))
> - return;
> + return 0;
>
> if (!sg_cpu->iowait_boost_pending) {
> /*
> @@ -294,7 +293,7 @@ static void sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time,
> sg_cpu->iowait_boost >>= 1;
> if (sg_cpu->iowait_boost < IOWAIT_BOOST_MIN) {
> sg_cpu->iowait_boost = 0;
> - return;
> + return 0;
> }
> }
>
> @@ -304,10 +303,7 @@ static void sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time,
> * sg_cpu->util is already in capacity scale; convert iowait_boost
> * into the same scale so we can compare.
> */
> - boost = (sg_cpu->iowait_boost * max_cap) >> SCHED_CAPACITY_SHIFT;
> - boost = uclamp_rq_util_with(cpu_rq(sg_cpu->cpu), boost, NULL);
> - if (sg_cpu->util < boost)
> - sg_cpu->util = boost;
> + return (sg_cpu->iowait_boost * max_cap) >> SCHED_CAPACITY_SHIFT;
> }
>
> #ifdef CONFIG_NO_HZ_COMMON
> @@ -337,6 +333,8 @@ 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;
>
> @@ -345,8 +343,8 @@ static inline bool sugov_update_single_common(struct sugov_cpu *sg_cpu,
> if (!sugov_should_update_freq(sg_cpu->sg_policy, time))
> return false;
>
> - sugov_get_util(sg_cpu);
> - sugov_iowait_apply(sg_cpu, time, max_cap);
> + boost = sugov_iowait_apply(sg_cpu, time, max_cap);
> + sugov_get_util(sg_cpu, boost);
>
> return true;
> }
> @@ -447,9 +445,10 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time)
>
> for_each_cpu(j, policy->cpus) {
> struct sugov_cpu *j_sg_cpu = &per_cpu(sugov_cpu, j);
> + unsigned long boost;
>
> - sugov_get_util(j_sg_cpu);
> - sugov_iowait_apply(j_sg_cpu, time, max_cap);
> + boost = sugov_iowait_apply(j_sg_cpu, time, max_cap);
> + sugov_get_util(j_sg_cpu, boost);
>
> util = max(j_sg_cpu->util, util);
> }
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 3873b4de7cfa..b181edaf4d41 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -3026,59 +3026,6 @@ static inline bool uclamp_rq_is_idle(struct rq *rq)
> return rq->uclamp_flags & UCLAMP_FLAG_IDLE;
> }
>
> -/**
> - * uclamp_rq_util_with - clamp @util with @rq and @p effective uclamp values.
> - * @rq: The rq to clamp against. Must not be NULL.
> - * @util: The util value to clamp.
> - * @p: The task to clamp against. Can be NULL if you want to clamp
> - * against @rq only.
> - *
> - * Clamps the passed @util to the max(@rq, @p) effective uclamp values.
> - *
> - * If sched_uclamp_used static key is disabled, then just return the util
> - * without any clamping since uclamp aggregation at the rq level in the fast
> - * path is disabled, rendering this operation a NOP.
> - *
> - * Use uclamp_eff_value() if you don't care about uclamp values at rq level. It
> - * will return the correct effective uclamp value of the task even if the
> - * static key is disabled.
> - */
> -static __always_inline
> -unsigned long uclamp_rq_util_with(struct rq *rq, unsigned long util,
> - struct task_struct *p)
> -{
> - unsigned long min_util = 0;
> - unsigned long max_util = 0;
> -
> - if (!static_branch_likely(&sched_uclamp_used))
> - return util;
> -
> - if (p) {
> - min_util = uclamp_eff_value(p, UCLAMP_MIN);
> - max_util = uclamp_eff_value(p, UCLAMP_MAX);
> -
> - /*
> - * Ignore last runnable task's max clamp, as this task will
> - * reset it. Similarly, no need to read the rq's min clamp.
> - */
> - if (uclamp_rq_is_idle(rq))
> - goto out;
> - }
> -
> - min_util = max_t(unsigned long, min_util, uclamp_rq_get(rq, UCLAMP_MIN));
> - max_util = max_t(unsigned long, max_util, uclamp_rq_get(rq, UCLAMP_MAX));
> -out:
> - /*
> - * Since CPU's {min,max}_util clamps are MAX aggregated considering
> - * RUNNABLE tasks with _different_ clamps, we can end up with an
> - * inversion. Fix it now when the clamps are applied.
> - */
> - if (unlikely(min_util >= max_util))
> - return min_util;
> -
> - return clamp(util, min_util, max_util);
> -}
> -
> /* Is the rq being capped/throttled by uclamp_max? */
> static inline bool uclamp_rq_is_capped(struct rq *rq)
> {
> @@ -3116,13 +3063,6 @@ static inline unsigned long uclamp_eff_value(struct task_struct *p,
> return SCHED_CAPACITY_SCALE;
> }
>
> -static inline
> -unsigned long uclamp_rq_util_with(struct rq *rq, unsigned long util,
> - struct task_struct *p)
> -{
> - return util;
> -}
> -
> static inline bool uclamp_rq_is_capped(struct rq *rq) { return false; }
>
> static inline bool uclamp_is_used(void)
> --
> 2.34.1
>
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