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Message-ID: <20221223115845.3azncwqlyo4zx262@airbuntu>
Date: Fri, 23 Dec 2022 11:58:45 +0000
From: Qais Yousef <qyousef@...alina.io>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Viresh Kumar <viresh.kumar@...aro.org>,
linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
Lukasz Luba <lukasz.luba@....com>, Wei Wang <wvw@...gle.com>,
Xuewen Yan <xuewen.yan94@...il.com>,
Hank <han.lin@...iatek.com>,
Jonathan JMChen <Jonathan.JMChen@...iatek.com>
Subject: Re: [RFC PATCH 3/3] sched/fair: Traverse cpufreq policies to detect
capacity inversion
On 12/20/22 14:50, Vincent Guittot wrote:
Thanks for the patch!
> Hereafter is what I came with in order to decouple misfit task with cpu
> overutilized. We keep using util_fits_cpu but with 3 values so we can keep
> using it with cpu_overutilized but exclude the case of misfit task
> because uclmap_min. Also select_idle_capacity() and feec() keep selecting the
> big cpu even if it doesn't fit only because of uclamp_min
>
>
> Subject: [PATCH] sched/fair: unlink misfit task from cpu overutilized
>
> By taking into account uclamp_min, the 1:1 relation between task misfit and
> cpu overutilized is no more true as a task with a util_avg of 20as an
> example may not fit a 1024 capacity cpu because of a uclamp_min constraint.
>
> Add a new state in util_fits_cpu() to reflect the case that task would fit
> a CPU except for the uclamp_min hint which is a bandwidth requriement.
nit: mixing uclamp with bandwidth has been a source of a lot of confusion when
discussing uclamp. Can we use performance requirement instead please?
>
> Use -1 to reflect that a CPU doesn't fit only because of uclamp_min so we
> can use this new value to take additional action to select the best cpu
> that doesn't match uclamp_min.
>
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> ---
> kernel/sched/fair.c | 73 ++++++++++++++++++++++++++++++---------------
> 1 file changed, 49 insertions(+), 24 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 4423681baf15..705335d6af65 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4578,8 +4578,7 @@ static inline int util_fits_cpu(unsigned long util,
> * 2. The system is being saturated when we're operating near
> * max capacity, it doesn't make sense to block overutilized.
> */
> - uclamp_max_fits = (capacity_orig == SCHED_CAPACITY_SCALE) && (uclamp_max == SCHED_CAPACITY_SCALE);
> - uclamp_max_fits = !uclamp_max_fits && (uclamp_max <= capacity_orig);
> + uclamp_max_fits = (uclamp_max <= capacity_orig) || (capacity_orig == SCHED_CAPACITY_SCALE);
> fits = fits || uclamp_max_fits;
>
> /*
> @@ -4614,8 +4613,8 @@ static inline int util_fits_cpu(unsigned long util,
> * handle the case uclamp_min > uclamp_max.
> */
> uclamp_min = min(uclamp_min, uclamp_max);
> - if (util < uclamp_min && capacity_orig != SCHED_CAPACITY_SCALE)
> - fits = fits && (uclamp_min <= capacity_orig_thermal);
> + if (fits && (util < uclamp_min) && (uclamp_min > capacity_orig_thermal))
> + return -1;
>
> return fits;
nit: return !!fits?
We check explicitly == 1 below and I'm not sure all the boolean check above
will guarantee we will end up return 1 for true on all combination of
compilerls/archs.
> }
> @@ -4625,7 +4624,7 @@ static inline int task_fits_cpu(struct task_struct *p, int cpu)
> unsigned long uclamp_min = uclamp_eff_value(p, UCLAMP_MIN);
> unsigned long uclamp_max = uclamp_eff_value(p, UCLAMP_MAX);
> unsigned long util = task_util_est(p);
> - return util_fits_cpu(util, uclamp_min, uclamp_max, cpu);
> + return (util_fits_cpu(util, uclamp_min, uclamp_max, cpu) == 1);
Or make this > 0?
> }
>
> static inline void update_misfit_status(struct task_struct *p, struct rq *rq)
> @@ -6064,7 +6063,10 @@ static inline void hrtick_update(struct rq *rq)
> #ifdef CONFIG_SMP
> static inline bool cpu_overutilized(int cpu)
> {
> - return !fits_capacity(cpu_util_cfs(cpu), capacity_of(cpu));
> + unsigned long rq_util_min = uclamp_rq_get(cpu_rq(cpu), UCLAMP_MIN);
> + unsigned long rq_util_max = uclamp_rq_get(cpu_rq(cpu), UCLAMP_MAX);
> +
> + return !util_fits_cpu(cpu_util_cfs(cpu), rq_util_min, rq_util_max, cpu);
> }
>
> static inline void update_overutilized_status(struct rq *rq)
> @@ -6857,6 +6859,7 @@ static int
> select_idle_capacity(struct task_struct *p, struct sched_domain *sd, int target)
> {
> unsigned long task_util, util_min, util_max, best_cap = 0;
> + int fits, best_fits = -1;
> int cpu, best_cpu = -1;
> struct cpumask *cpus;
>
> @@ -6872,12 +6875,24 @@ select_idle_capacity(struct task_struct *p, struct sched_domain *sd, int target)
>
> if (!available_idle_cpu(cpu) && !sched_idle_cpu(cpu))
> continue;
> - if (util_fits_cpu(task_util, util_min, util_max, cpu))
> +
> + fits = util_fits_cpu(task_util, util_min, util_max, cpu);
> +
> + /* This cpu fits with all capacity requirements */
nit: s#capacity#capacity & performance#?
> + if (fits > 0)
> return cpu;
> + /*
> + * Only the min bandwidth (i.e. uclamp_min) doesn't fit. Look
> + * for the cpu with highest bandwidth capacity.
> + */
s/bandwidth/performance/?
> + else if (fits < 0)
> + cpu_cap = capacity_of(cpu) - thermal_load_avg(cpu_rq(cpu));
Hmm. Isn't capacity_of() already takes into account thermal_load_avg()?
Did you mean capacity_orig_of()?
>
> - if (cpu_cap > best_cap) {
> + if ((fits > best_fits) ||
> + ((fits == best_fits) && (cpu_cap > best_cap))) {
> best_cap = cpu_cap;
> best_cpu = cpu;
> + best_fits = fits;
I'm not sure if this logic is correct. It's a bit of a mind bender.
@iter#0
fits <= 0
best_fits <= -1
if (fits > best_fits) // 0 > -1 => True
... // update best_cap if larger
best_fits <= 0
@iter#1
fits <= -1
best_fits <= 0
if (fits > best_fits) // -1 > 0 => False
if (fits == best_fits) // -1 == 0 => False
// We will never update best_cap for all fits = -1 after
// encountering the first fits = 0
I think we should reverse the initial values and split the conditions
int fits, best_fits = 0;
if ((fits < best_fits)) {
/* Reset best_cap for first "fits_but" */
best_cap = cpu_cap;
best_cpu = cpu;
best_fits = fits;
} else if ((fits == best_fits) && (cpu_cap > best_cap))) {
best_cap = cpu_cap;
best_cpu = cpu;
}
Which give us
@iter#0
fits <= 0
best_fits <= 0
if (fits < best_fits) // 0 < 0 => False
if (fits == best_fits) // 0 == 0 => True
... // update best_cap if larger
@iter#1
fits <= -1
best_fits <= 0
if (fits < best_fits) // -1 < 0 => True
... // reset best_cap to first "fits_but" hit
best_fits <= -1
@iter#2
fits <= 0
best_fits <= -1
if (fits < best_fits) // 0 < -1 => False
if (fits == best_fits) // 0 == -1 => False
// We should never update best_cap for all fits == 0 now
@iter#3
fits <= -1
best_fits <= -1
if (fits < best_fits) // -1 < -1 => False
if (fits == best_fits) // -1 == -1 => True
... // update best_cap if larger
// Only fits = -1 will update best_cap if larger now
Of course any hit with fits = 1 will return the cpu immediately.
> }
> }
>
> @@ -6890,7 +6905,7 @@ static inline bool asym_fits_cpu(unsigned long util,
> int cpu)
> {
> if (sched_asym_cpucap_active())
> - return util_fits_cpu(util, util_min, util_max, cpu);
> + return (util_fits_cpu(util, util_min, util_max, cpu) > 0);
>
> return true;
> }
> @@ -7257,6 +7272,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> unsigned long p_util_max = uclamp_is_used() ? uclamp_eff_value(p, UCLAMP_MAX) : 1024;
> struct root_domain *rd = this_rq()->rd;
> int cpu, best_energy_cpu, target = -1;
> + int prev_fits = -1, best_fits = -1;
> struct sched_domain *sd;
> struct perf_domain *pd;
> struct energy_env eenv;
> @@ -7288,10 +7304,11 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> unsigned long cpu_cap, cpu_thermal_cap, util;
> unsigned long cur_delta, max_spare_cap = 0;
> unsigned long rq_util_min, rq_util_max;
> - unsigned long util_min, util_max;
> + unsigned long util_min = 0, util_max = 1024;
Why this change? Are you hitting the same warning reported by Dan?
> unsigned long prev_spare_cap = 0;
> int max_spare_cap_cpu = -1;
> unsigned long base_energy;
> + int fits, max_fits = -1;
>
> cpumask_and(cpus, perf_domain_span(pd), cpu_online_mask);
>
> @@ -7344,7 +7361,9 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> util_max = max(rq_util_max, p_util_max);
> }
> }
> - if (!util_fits_cpu(util, util_min, util_max, cpu))
> +
> + fits = util_fits_cpu(util, util_min, util_max, cpu);
> + if (!fits)
> continue;
>
> lsub_positive(&cpu_cap, util);
> @@ -7352,7 +7371,9 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> if (cpu == prev_cpu) {
> /* Always use prev_cpu as a candidate. */
> prev_spare_cap = cpu_cap;
> - } else if (cpu_cap > max_spare_cap) {
> + prev_fits = fits;
> + } else if ((fits > max_fits) ||
> + ((fits == max_fits) && (cpu_cap > max_spare_cap))) {
> /*
> * Find the CPU with the maximum spare capacity
> * among the remaining CPUs in the performance
> @@ -7360,6 +7381,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> */
> max_spare_cap = cpu_cap;
> max_spare_cap_cpu = cpu;
> + max_fits = fits;
Should we reset best_delta here?
Because we update max_fits here..
> }
> }
>
> @@ -7389,15 +7411,18 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> if (cur_delta < base_energy)
> goto unlock;
> cur_delta -= base_energy;
> - if (cur_delta < best_delta) {
> + if ((fits > max_fits) ||
> + ((fits == max_fits) && (cur_delta < best_delta))) {
.. on first first transitions from -1 to 1; this condition will be
skipped if cur_delta is lower than best delta. best_delta here could be the
previous -1 fitting cpu.
We should reset best_delta on first transition then look if we encounter
something with a better delta?
Thanks!
--
Qais Yousef
> best_delta = cur_delta;
> best_energy_cpu = max_spare_cap_cpu;
> + best_fits = max_fits;
> }
> }
> }
> rcu_read_unlock();
>
> - if (best_delta < prev_delta)
> + if ((best_fits > prev_fits) ||
> + ((best_fits == prev_fits) && (best_delta < prev_delta)))
> target = best_energy_cpu;
>
> return target;
> @@ -10164,24 +10189,23 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
> */
> update_sd_lb_stats(env, &sds);
>
> - if (sched_energy_enabled()) {
> - struct root_domain *rd = env->dst_rq->rd;
> -
> - if (rcu_dereference(rd->pd) && !READ_ONCE(rd->overutilized))
> - goto out_balanced;
> - }
> -
> - local = &sds.local_stat;
> - busiest = &sds.busiest_stat;
> -
> /* There is no busy sibling group to pull tasks from */
> if (!sds.busiest)
> goto out_balanced;
>
> + busiest = &sds.busiest_stat;
> +
> /* Misfit tasks should be dealt with regardless of the avg load */
> if (busiest->group_type == group_misfit_task)
> goto force_balance;
>
> + if (sched_energy_enabled()) {
> + struct root_domain *rd = env->dst_rq->rd;
> +
> + if (rcu_dereference(rd->pd) && !READ_ONCE(rd->overutilized))
> + goto out_balanced;
> + }
> +
> /* ASYM feature bypasses nice load balance check */
> if (busiest->group_type == group_asym_packing)
> goto force_balance;
> @@ -10194,6 +10218,7 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
> if (busiest->group_type == group_imbalanced)
> goto force_balance;
>
> + local = &sds.local_stat;
> /*
> * If the local group is busier than the selected busiest group
> * don't try and pull any tasks.
> --
> 2.17.1
>
>
>
> >
> >
> > Thanks!!
> >
> > --
> > Qais Yousef
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