Messages in this thread |  | | From | Vincent Guittot <> | | Date | Mon, 16 Jan 2023 12:23:24 +0100 | | Subject | Re: [PATCH v3] sched/fair: unlink misfit task from cpu overutilized |
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On Mon, 16 Jan 2023 at 10:07, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote: > > On 13/01/2023 14:40, Vincent Guittot wrote: > > 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 small util_avg of > > of ? > > > may not fit a high capacity cpu because of 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 performance requirement. > > > > 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 hint. > > > > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> > > --- > > > > Change since v2: > > - fix a condition in feec() > > - add comments > > > > kernel/sched/fair.c | 108 ++++++++++++++++++++++++++++++++++---------- > > 1 file changed, 83 insertions(+), 25 deletions(-) > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index e9d906a9bba9..29adb9e27b3d 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -4525,8 +4525,7 @@ 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); > > Isn't `uclamp_max <= capacity_orig` always true for `capacity_orig == > SCHED_CAPACITY_SCALE`? > > uclamp_max = [0..SCHED_CAPACITY_SCALE] , capacity_orig = > SCHED_CAPACITY_SCALE > > > fits = fits || uclamp_max_fits; > > Like Qais I don't understand this change. I read the previous discussion > from https://lkml.kernel.org/r/20221208140526.vvmjxlz6akgqyoma@airbuntu > ("Re: [RFC PATCH 3/3] sched/fair: Traverse cpufreq policies to detect > capacity inversion"). > > I assume Qais wanted to force `uclamp_max_fits = 0` for a big CPU > (`capacity_orig = 1024`) and a `uclamp_max = 1024` to not lift `fits` > from 0 to 1. > > > /* > > @@ -4561,8 +4560,8 @@ 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; > > } > > @@ -4572,7 +4571,11 @@ 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 true only if the cpu fully fits the task requirements, which > > + * include the utilization but also the performance. > > Not sure if people get what `performance requirements` mean here? I know > we want to use `performance` rather `bandwidth hint` to describe what > uclamp is. So shouldn't we use `utilization but also uclamp`? > > > + */ > > + return (util_fits_cpu(util, uclamp_min, uclamp_max, cpu) > 0); > > } > > > > static inline void update_misfit_status(struct task_struct *p, struct rq *rq) > > @@ -6132,6 +6135,7 @@ static inline bool cpu_overutilized(int 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 true only if the utlization doesn't fit its capacity */ > > s/utlization/utilization > s/its/CPU ? > > > return !util_fits_cpu(cpu_util_cfs(cpu), rq_util_min, rq_util_max, cpu); > > } > > cpu_overutilized() is the only place where we now only test for > !util_fits_cpu(). The new comment says we only care about utilization > not fitting CPU capacity. > > Does this mean the rq uclamp values are not important here and we could > go back to use fits_capacity()? > > Not sure since util_fits_cpu() is still coded differently:
uclamp_min is not important but uclamp_max still cap the utilization
> > fits = fits_capacity(util, capacity) > > fits = fits || uclamp_max_fits <-- uclamp_max_fits can turn fits from > 0 into 1, so util doesn't fit but > we don't return 1? > > That said, I don't understand the current 'uclamp_max_fits = (uclamp_max > <= capacity_orig) || (capacity_orig == SCHED_CAPACITY_SCALE)' in > util_fits_cpu(), like already mentioned. > > > @@ -6925,6 +6929,7 @@ 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 = 0; > > int cpu, best_cpu = -1; > > struct cpumask *cpus; > > > > @@ -6940,12 +6945,28 @@ 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 and performance requirements */ > > In task_fits_cpu() `utilization and performance (better uclamp) > requirements` term was used. I assume it's the same thing here? > > > + if (fits > 0) > > return cpu; > > + /* > > + * Only the min performance (i.e. uclamp_min) doesn't fit. Look > > + * for the CPU with highest performance capacity. > ^^^^^^^^^^^^^^^^^^^^ > > Do we use a new CPU capacity value `performance capacity (1)` here? > > Which I guess is `capacity_orig_of(cpu) - thermal_load_avg(cpu_rq(cpu)`. > > I'm asking since util_fits_cpu() still uses: `capacity_orig_thermal (2) > = capacity_orig - arch_scale_thermal_pressure()` when checking whether > to return -1. Shouldn't (1) and (2) be the same?
I'm all in favor of both being capacity_orig_of(cpu) - thermal_load_avg(cpu_rq(cpu) like the capacity inversion detection
> > > + */ > > + else if (fits < 0) > > + cpu_cap = capacity_orig_of(cpu) - thermal_load_avg(cpu_rq(cpu)); > > > > - if (cpu_cap > best_cap) { > > + /* > > + * First, select cpu which fits better (-1 being better than 0). > > + * Then, select the one with largest capacity at same level. > > + */ > > + if ((fits < best_fits) || > > + ((fits == best_fits) && (cpu_cap > best_cap))) { > > best_cap = cpu_cap; > > best_cpu = cpu; > > + best_fits = fits; > > } > > } > > > > [...] > > > @@ -7446,26 +7480,50 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) > > if (prev_delta < base_energy) > > goto unlock; > > prev_delta -= base_energy; > > + prev_thermal_cap = cpu_thermal_cap; > > best_delta = min(best_delta, prev_delta); > > } > > > > /* Evaluate the energy impact of using max_spare_cap_cpu. */ > > if (max_spare_cap_cpu >= 0 && max_spare_cap > prev_spare_cap) { > > + /* Current best energy cpu fits better */ > > + if (max_fits < best_fits) > > + continue; > > + > > + /* > > + * Both don't fit performance (i.e. uclamp_min) but > > + * best energy cpu has better performance. > > IMHO, `performance` stands for `cpu_thermal_cap` which is > `cpu_capacity_orig - thermal pressure`. > > I assume `performance` is equal to `performance capacity` used in > select_idle_capacity which uses thermal_load_avg() and not thermal > pressure. Why this difference? > > [...]
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