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Date: Mon, 23 Nov 2020 10:54:56 +1100 From: Balbir Singh <bsingharora@...il.com> To: "Joel Fernandes (Google)" <joel@...lfernandes.org> Cc: Nishanth Aravamudan <naravamudan@...italocean.com>, Julien Desfossez <jdesfossez@...italocean.com>, Peter Zijlstra <peterz@...radead.org>, Tim Chen <tim.c.chen@...ux.intel.com>, Vineeth Pillai <viremana@...ux.microsoft.com>, Aaron Lu <aaron.lwe@...il.com>, Aubrey Li <aubrey.intel@...il.com>, tglx@...utronix.de, linux-kernel@...r.kernel.org, mingo@...nel.org, torvalds@...ux-foundation.org, fweisbec@...il.com, keescook@...omium.org, kerrnel@...gle.com, Phil Auld <pauld@...hat.com>, Valentin Schneider <valentin.schneider@....com>, Mel Gorman <mgorman@...hsingularity.net>, Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, Paolo Bonzini <pbonzini@...hat.com>, vineeth@...byteword.org, Chen Yu <yu.c.chen@...el.com>, Christian Brauner <christian.brauner@...ntu.com>, Agata Gruza <agata.gruza@...el.com>, Antonio Gomez Iglesias <antonio.gomez.iglesias@...el.com>, graf@...zon.com, konrad.wilk@...cle.com, dfaggioli@...e.com, pjt@...gle.com, rostedt@...dmis.org, derkling@...gle.com, benbjiang@...cent.com, Alexandre Chartre <alexandre.chartre@...cle.com>, James.Bottomley@...senpartnership.com, OWeisse@...ch.edu, Dhaval Giani <dhaval.giani@...cle.com>, Junaid Shahid <junaids@...gle.com>, jsbarnes@...gle.com, chris.hyser@...cle.com, Ben Segall <bsegall@...gle.com>, Josh Don <joshdon@...gle.com>, Hao Luo <haoluo@...gle.com>, Tom Lendacky <thomas.lendacky@....com>, Aubrey Li <aubrey.li@...el.com>, Aubrey Li <aubrey.li@...ux.intel.com>, "Paul E. McKenney" <paulmck@...nel.org>, Tim Chen <tim.c.chen@...el.com> Subject: Re: [PATCH -tip 14/32] sched: migration changes for core scheduling On Tue, Nov 17, 2020 at 06:19:44PM -0500, Joel Fernandes (Google) wrote: > From: Aubrey Li <aubrey.li@...el.com> > > - 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@...italocean.com> > Signed-off-by: Aubrey Li <aubrey.li@...ux.intel.com> > Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com> > Signed-off-by: Vineeth Remanan Pillai <viremana@...ux.microsoft.com> > Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org> > --- > kernel/sched/fair.c | 64 ++++++++++++++++++++++++++++++++++++++++---- > kernel/sched/sched.h | 29 ++++++++++++++++++++ > 2 files changed, 88 insertions(+), 5 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index de82f88ba98c..ceb3906c9a8a 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -1921,6 +1921,15 @@ static void task_numa_find_cpu(struct task_numa_env *env, > if (!cpumask_test_cpu(cpu, env->p->cpus_ptr)) > continue; > > +#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? > env->dst_cpu = cpu; > if (task_numa_compare(env, taskimp, groupimp, maymove)) > break; > @@ -5867,11 +5876,17 @@ 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); > + > +#ifdef CONFIG_SCHED_CORE > + if (!sched_core_cookie_match(rq, p)) > + continue; > +#endif > + > 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 +6144,18 @@ 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)) { > +#ifdef CONFIG_SCHED_CORE > + /* > + * If Core Scheduling is enabled, select this cpu > + * only if the process cookie matches core cookie. > + */ > + if (sched_core_enabled(cpu_rq(cpu)) && > + p->core_cookie == cpu_rq(cpu)->core->core_cookie) > +#endif > + break; > + } > } > > time = cpu_clock(this) - time; > @@ -7530,8 +7555,9 @@ 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 +7592,15 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env) > return 0; > } > > +#ifdef CONFIG_SCHED_CORE > + /* > + * 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; > +#endif > + > /* Record that we found atleast one task that could run on dst_cpu */ > env->flags &= ~LBF_ALL_PINNED; > > @@ -8792,6 +8827,25 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, int this_cpu) > p->cpus_ptr)) > continue; > > +#ifdef CONFIG_SCHED_CORE > + 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; > + } > +#endif > + > 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..de553d39aa40 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -1135,6 +1135,35 @@ 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 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)) { I was looking at this snippet and comparing this to is_core_idle(), the major difference is the check for vcpu_is_preempted(). Do we want to call the core as non idle if any vcpu was preempted on this CPU? > + idle_core = false; > + break; > + } > + } > + > + /* > + * A CPU in an idle core is always the best choice for tasks with > + * cookies. > + */ > + return idle_core || rq->core->core_cookie == p->core_cookie; > +} > + Balbir Singh.
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