Messages in this thread | ![/](/images/icornerl.gif) | | From | Vincent Guittot <> | Date | Mon, 16 Jan 2023 12:08:27 +0100 | Subject | Re: [PATCH v3] sched/fair: unlink misfit task from cpu overutilized |
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On Sun, 15 Jan 2023 at 01:19, Qais Yousef <qyousef@layalina.io> wrote: > > On 01/13/23 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 > > 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); > > I think this hunk is what is causing the overutilized issues Kajetan reported > against your patch.
Yeah, I have been to agressive with uclamp_max
> > For the big cpu, this expression will always be true. So overutilized will > trigger only for little and medium cores. > > I appreciate writing the boolean in a shorter form might appear like less code, > but it makes things harder to read too; the compiler should be good at > simplifying the expression if it can, no? > > Shall we leave the original expression as-is since it's easier to reason about? > > I think already by 'saving' using another variable we reduced readability and > lead to this error. First line checks if we are the max_capacity which is > the corner case we'd like to avoid and accidentally lost > > v1 code was: > > + max_capacity = (capacity_orig == SCHED_CAPACITY_SCALE) && (uclamp_max == SCHED_CAPACITY_SCALE); > + uclamp_max_fits = !max_capacity && (uclamp_max <= capacity_orig); > + fits = fits || uclamp_max_fits; > > I think that extra variable was well named to help make it obvious what corner > case we're trying to catch here. Especially it matches the comment above it > explaining this corner case. This auto variable should be free, no? > > Can we go back to this form please?
Yes, I'm going to come back to previous version
> > > fits = fits || uclamp_max_fits; > > > > /* > > @@ -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; > > Here shouldn't this be > > if (util < uclamp_min) { > fits = fits && (uclamp_min <= capacity_orig); > if (fits && (uclamp_min > capacity_orig_thermal)) > return -1; > } > > uclamp_min should fit capacity_orig first then we'd check for the corner case
I don't get why we should test capacity_orig first ?
case 1: capacity_orig = 800 uclamp_min = 512 capacity_orig_thermal = 400 util = 200 util_fits_cpu should return -1
case 2: uclamp_min = 900 capacity_orig = 800 capacity_orig_thermal = 400 utili_avg = 200 util_fits_cpu should return -1 whereas with your proposal above it will return 0
> if thermal pressure is causing it not to fit. And all of this should only > matter if utill < uclamp_min. Otherwise util_avg should be driving force if > uclamp_max is not trumping it. > > I need time to update my unit test [1] to catch these error cases as I didn't > see them. In the next version I think it's worth including the changes to > remove the capacity inversion in the patch. > > [1] https://github.com/qais-yousef/uclamp_test/blob/master/uclamp_test_thermal_pressure.c > > > Thanks! > > -- > Qais Yousef > > > > > 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. > > + */ > > + 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 */ > > return !util_fits_cpu(cpu_util_cfs(cpu), rq_util_min, rq_util_max, cpu); > > } > > > > @@ -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 */ > > + if (fits > 0) > > return cpu; > > + /* > > + * Only the min performance (i.e. uclamp_min) doesn't fit. Look > > + * for the CPU with highest performance capacity. > > + */ > > + 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; > > } > > } > > > > @@ -6958,7 +6979,11 @@ 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 true only if the cpu fully fits the task requirements > > + * which include the utilization but also the performance. > > + */ > > + return (util_fits_cpu(util, util_min, util_max, cpu) > 0); > > > > return true; > > } > > @@ -7325,6 +7350,9 @@ 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; > > + unsigned long best_thermal_cap = 0; > > + unsigned long prev_thermal_cap = 0; > > struct sched_domain *sd; > > struct perf_domain *pd; > > struct energy_env eenv; > > @@ -7360,6 +7388,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) > > 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); > > > > @@ -7412,7 +7441,9 @@ 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); > > @@ -7420,7 +7451,9 @@ 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 > > @@ -7428,6 +7461,7 @@ 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; > > } > > } > > > > @@ -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. > > + */ > > + if ((max_fits < 0) && > > + (cpu_thermal_cap <= best_thermal_cap)) > > + continue; > > + > > cur_delta = compute_energy(&eenv, pd, cpus, p, > > max_spare_cap_cpu); > > /* CPU utilization has changed */ > > if (cur_delta < base_energy) > > goto unlock; > > cur_delta -= base_energy; > > - if (cur_delta < best_delta) { > > - best_delta = cur_delta; > > - best_energy_cpu = max_spare_cap_cpu; > > - } > > + > > + /* > > + * Both fit for the task but best energy cpu has lower > > + * energy impact. > > + */ > > + if ((max_fits > 0) && (best_fits > 0) && > > + (cur_delta >= best_delta)) > > + continue; > > + > > + best_delta = cur_delta; > > + best_energy_cpu = max_spare_cap_cpu; > > + best_fits = max_fits; > > + best_thermal_cap = cpu_thermal_cap; > > } > > } > > rcu_read_unlock(); > > > > - if (best_delta < prev_delta) > > + if ((best_fits > prev_fits) || > > + ((best_fits > 0) && (best_delta < prev_delta)) || > > + ((best_fits < 0) && (best_thermal_cap > prev_thermal_cap))) > > target = best_energy_cpu; > > > > return target; > > @@ -10259,24 +10317,23 @@ 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; > > @@ -10289,6 +10346,7 @@ 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. > > -- > > 2.34.1 > >
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