Messages in this thread | | | Subject | Re: [PATCH -tip 14/32] sched: migration changes for core scheduling | From | "Li, Aubrey" <> | Date | Thu, 26 Nov 2020 17:26:31 +0800 |
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On 2020/11/26 16:32, Balbir Singh wrote: > On Thu, Nov 26, 2020 at 11:20:41AM +0800, Li, Aubrey wrote: >> On 2020/11/26 6:57, Balbir Singh wrote: >>> On Wed, Nov 25, 2020 at 11:12:53AM +0800, Li, Aubrey wrote: >>>> On 2020/11/24 23:42, Peter Zijlstra wrote: >>>>> On Mon, Nov 23, 2020 at 12:36:10PM +0800, Li, Aubrey wrote: >>>>>>>> +#ifdef CONFIG_SCHED_CORE >>>>>>>> + /* >>>>>>>> + * Skip this cpu if source task's cookie does not match >>>>>>>> + * with CPU's core cookie. >>>>>>>> + */ >>>>>>>> + if (!sched_core_cookie_match(cpu_rq(cpu), env->p)) >>>>>>>> + continue; >>>>>>>> +#endif >>>>>>>> + >>>>>>> >>>>>>> Any reason this is under an #ifdef? In sched_core_cookie_match() won't >>>>>>> the check for sched_core_enabled() do the right thing even when >>>>>>> CONFIG_SCHED_CORE is not enabed?> >>>>>> Yes, sched_core_enabled works properly when CONFIG_SCHED_CORE is not >>>>>> enabled. But when CONFIG_SCHED_CORE is not enabled, it does not make >>>>>> sense to leave a core scheduler specific function here even at compile >>>>>> time. Also, for the cases in hot path, this saves CPU cycles to avoid >>>>>> a judgment. >>>>> >>>>> No, that's nonsense. If it works, remove the #ifdef. Less (#ifdef) is >>>>> more. >>>>> >>>> >>>> Okay, I pasted the refined patch here. >>>> @Joel, please let me know if you want me to send it in a separated thread. >>>> >>> >>> You still have a bunch of #ifdefs, can't we just do >>> >>> #ifndef CONFIG_SCHED_CORE >>> static inline bool sched_core_enabled(struct rq *rq) >>> { >>> return false; >>> } >>> #endif >>> >>> and frankly I think even that is not needed because there is a jump >>> label __sched_core_enabled that tells us if sched_core is enabled or >>> not. >> >> Hmm..., I need another wrapper for CONFIG_SCHED_CORE specific variables. >> How about this one? >> > > Much better :) > >> Thanks, >> -Aubrey >> >> From 61dac9067e66b5b9ea26c684c8c8235714bab38a Mon Sep 17 00:00:00 2001 >> From: Aubrey Li <aubrey.li@linux.intel.com> >> Date: Thu, 26 Nov 2020 03:08:04 +0000 >> Subject: [PATCH] sched: migration changes for core scheduling >> >> - Don't migrate if there is a cookie mismatch >> Load balance tries to move task from busiest CPU to the >> destination CPU. When core scheduling is enabled, if the >> task's cookie does not match with the destination CPU's >> core cookie, this task will be skipped by this CPU. This >> mitigates the forced idle time on the destination CPU. >> >> - Select cookie matched idle CPU >> In the fast path of task wakeup, select the first cookie matched >> idle CPU instead of the first idle CPU. >> >> - Find cookie matched idlest CPU >> In the slow path of task wakeup, find the idlest CPU whose core >> cookie matches with task's cookie >> >> - Don't migrate task if cookie not match >> For the NUMA load balance, don't migrate task to the CPU whose >> core cookie does not match with task's cookie >> >> Tested-by: Julien Desfossez <jdesfossez@digitalocean.com> >> Signed-off-by: Aubrey Li <aubrey.li@linux.intel.com> >> Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com> >> Signed-off-by: Vineeth Remanan Pillai <viremana@linux.microsoft.com> >> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> >> --- >> kernel/sched/fair.c | 57 ++++++++++++++++++++++++++++++++++++++++---- >> kernel/sched/sched.h | 43 +++++++++++++++++++++++++++++++++ >> 2 files changed, 95 insertions(+), 5 deletions(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index de82f88ba98c..70dd013dff1d 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -1921,6 +1921,13 @@ static void task_numa_find_cpu(struct task_numa_env *env, >> if (!cpumask_test_cpu(cpu, env->p->cpus_ptr)) >> continue; >> >> + /* >> + * Skip this cpu if source task's cookie does not match >> + * with CPU's core cookie. >> + */ >> + if (!sched_core_cookie_match(cpu_rq(cpu), env->p)) >> + continue; >> + >> env->dst_cpu = cpu; >> if (task_numa_compare(env, taskimp, groupimp, maymove)) >> break; >> @@ -5867,11 +5874,15 @@ find_idlest_group_cpu(struct sched_group *group, struct task_struct *p, int this >> >> /* Traverse only the allowed CPUs */ >> for_each_cpu_and(i, sched_group_span(group), p->cpus_ptr) { >> + struct rq *rq = cpu_rq(i); >> + >> + if (!sched_core_cookie_match(rq, p)) >> + continue; >> + >> if (sched_idle_cpu(i)) >> return i; >> >> if (available_idle_cpu(i)) { >> - struct rq *rq = cpu_rq(i); >> struct cpuidle_state *idle = idle_get_state(rq); >> if (idle && idle->exit_latency < min_exit_latency) { >> /* >> @@ -6129,8 +6140,19 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t >> for_each_cpu_wrap(cpu, cpus, target) { >> if (!--nr) >> return -1; >> - if (available_idle_cpu(cpu) || sched_idle_cpu(cpu)) >> - break; >> + >> + if (available_idle_cpu(cpu) || sched_idle_cpu(cpu)) { >> + /* >> + * If Core Scheduling is enabled, select this cpu >> + * only if the process cookie matches core cookie. >> + */ >> + if (sched_core_enabled(cpu_rq(cpu))) { >> + if (__cookie_match(cpu_rq(cpu), p)) >> + break; >> + } else { >> + break; >> + } >> + } > > Isn't this better and equivalent? > > if ((available_idle_cpu(cpu) || sched_idle_cpu(cpu)) && > sched_core_cookie_match(cpu_rq(cpu), p)) > break; >
That's my previous implementation in the earlier version. But since here is the hot code path, we want to remove the idle core check in sched_core_cookie_match.
>> } >> >> time = cpu_clock(this) - time; >> @@ -7530,8 +7552,9 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env) >> * We do not migrate tasks that are: >> * 1) throttled_lb_pair, or >> * 2) cannot be migrated to this CPU due to cpus_ptr, or >> - * 3) running (obviously), or >> - * 4) are cache-hot on their current CPU. >> + * 3) task's cookie does not match with this CPU's core cookie >> + * 4) running (obviously), or >> + * 5) are cache-hot on their current CPU. >> */ >> if (throttled_lb_pair(task_group(p), env->src_cpu, env->dst_cpu)) >> return 0; >> @@ -7566,6 +7589,13 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env) >> return 0; >> } >> >> + /* >> + * Don't migrate task if the task's cookie does not match >> + * with the destination CPU's core cookie. >> + */ >> + if (!sched_core_cookie_match(cpu_rq(env->dst_cpu), p)) >> + return 0; >> + >> /* Record that we found atleast one task that could run on dst_cpu */ >> env->flags &= ~LBF_ALL_PINNED; >> >> @@ -8792,6 +8822,23 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, int this_cpu) >> p->cpus_ptr)) >> continue; >> >> + if (sched_core_enabled(cpu_rq(this_cpu))) { >> + int i = 0; >> + bool cookie_match = false; >> + >> + for_each_cpu(i, sched_group_span(group)) { >> + struct rq *rq = cpu_rq(i); >> + >> + if (sched_core_cookie_match(rq, p)) { >> + cookie_match = true; >> + break; >> + } >> + } >> + /* Skip over this group if no cookie matched */ >> + if (!cookie_match) >> + continue; >> + } >> + > > Again, I think this can be refactored because sched_core_cookie_match checks > for sched_core_enabled() > > int i = 0; > bool cookie_match = false; > for_each_cpu(i, sched_group_span(group)) { > if (sched_core_cookie_match(cpu_rq(i), p)) > break; > } > if (i >= nr_cpu_ids) > continue;
There is a loop here when CONFIG_SCHED_CORE=n, which is unwanted I guess.
Thanks, -Aubrey
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