Messages in this thread Patch in this message | | | Date | Thu, 26 Nov 2020 19:32:50 +1100 | From | Balbir Singh <> | Subject | Re: [PATCH -tip 14/32] sched: migration changes for core scheduling |
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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;
> } > > 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;
> + } > + /* Skip over this group if no cookie matched */ > + if (!cookie_match) > + continue;
> local_group = cpumask_test_cpu(this_cpu, > sched_group_span(group)); > > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index e72942a9ee11..8bb3b72d593c 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -1135,6 +1135,40 @@ static inline raw_spinlock_t *rq_lockp(struct rq *rq) > > bool cfs_prio_less(struct task_struct *a, struct task_struct *b); > > +/* > + * Helper to check if the CPU's core cookie matches with the task's cookie > + * when core scheduling is enabled. > + * A special case is that the task's cookie always matches with CPU's core > + * cookie if the CPU is in an idle core. > + */ > +static inline bool __cookie_match(struct rq *rq, struct task_struct *p) > +{ > + return rq->core->core_cookie == p->core_cookie; > +} > + > +static inline bool sched_core_cookie_match(struct rq *rq, struct task_struct *p) > +{ > + bool idle_core = true; > + int cpu; > + > + /* Ignore cookie match if core scheduler is not enabled on the CPU. */ > + if (!sched_core_enabled(rq)) > + return true; > + > + for_each_cpu(cpu, cpu_smt_mask(cpu_of(rq))) { > + if (!available_idle_cpu(cpu)) { > + idle_core = false; > + break; > + } > + } > + > + /* > + * A CPU in an idle core is always the best choice for tasks with > + * cookies. > + */ > + return idle_core || __cookie_match(rq, p); > +} > + > extern void queue_core_balance(struct rq *rq); > > #else /* !CONFIG_SCHED_CORE */ > @@ -1153,6 +1187,15 @@ static inline void queue_core_balance(struct rq *rq) > { > } > > +static inline bool __cookie_match(struct rq *rq, struct task_struct *p) > +{ > + return true; > +} > + > +static inline bool sched_core_cookie_match(struct rq *rq, struct task_struct *p) > +{ > + return true; > +} > #endif /* CONFIG_SCHED_CORE */ > > #ifdef CONFIG_SCHED_SMT > -- > 2.17.1 >
Balbir Singh.
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