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...@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 <jdesfos...@digitalocean.com>
> Signed-off-by: Aubrey Li <aubrey...@linux.intel.com>
> Signed-off-by: Tim Chen <tim.c.c...@linux.intel.com>
> Signed-off-by: Vineeth Remanan Pillai <virem...@linux.microsoft.com>
> Signed-off-by: Joel Fernandes (Google) <j...@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.
