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Date: Wed, 25 Nov 2020 17:28:36 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
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>,
Thomas Gleixner <tglx@...utronix.de>,
linux-kernel <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...nel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Frederic Weisbecker <fweisbec@...il.com>,
Kees Cook <keescook@...omium.org>,
Greg Kerr <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,
Paul Turner <pjt@...gle.com>,
Steven Rostedt <rostedt@...dmis.org>,
Patrick Bellasi <derkling@...gle.com>,
Jiang Biao <benbjiang@...cent.com>,
Alexandre Chartre <alexandre.chartre@...cle.com>,
James Bottomley <James.Bottomley@...senpartnership.com>,
OWeisse@...ch.edu, Dhaval Giani <dhaval.giani@...cle.com>,
Junaid Shahid <junaids@...gle.com>, jsbarnes@...gle.com,
"Hyser,Chris" <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@...ux.intel.com>,
"Paul E. McKenney" <paulmck@...nel.org>,
Tim Chen <tim.c.chen@...el.com>
Subject: Re: [PATCH -tip 02/32] sched: Introduce sched_class::pick_task()
On Wed, 18 Nov 2020 at 00:20, Joel Fernandes (Google)
<joel@...lfernandes.org> wrote:
>
> From: Peter Zijlstra <peterz@...radead.org>
>
> Because sched_class::pick_next_task() also implies
> sched_class::set_next_task() (and possibly put_prev_task() and
> newidle_balance) it is not state invariant. This makes it unsuitable
> for remote task selection.
>
> Tested-by: Julien Desfossez <jdesfossez@...italocean.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Signed-off-by: Vineeth Remanan Pillai <viremana@...ux.microsoft.com>
> Signed-off-by: Julien Desfossez <jdesfossez@...italocean.com>
> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> ---
> kernel/sched/deadline.c | 16 ++++++++++++++--
> kernel/sched/fair.c | 32 +++++++++++++++++++++++++++++++-
> kernel/sched/idle.c | 8 ++++++++
> kernel/sched/rt.c | 15 +++++++++++++--
> kernel/sched/sched.h | 3 +++
> kernel/sched/stop_task.c | 14 ++++++++++++--
> 6 files changed, 81 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 0f2ea0a3664c..abfc8b505d0d 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1867,7 +1867,7 @@ static struct sched_dl_entity *pick_next_dl_entity(struct rq *rq,
> return rb_entry(left, struct sched_dl_entity, rb_node);
> }
>
> -static struct task_struct *pick_next_task_dl(struct rq *rq)
> +static struct task_struct *pick_task_dl(struct rq *rq)
> {
> struct sched_dl_entity *dl_se;
> struct dl_rq *dl_rq = &rq->dl;
> @@ -1879,7 +1879,18 @@ static struct task_struct *pick_next_task_dl(struct rq *rq)
> dl_se = pick_next_dl_entity(rq, dl_rq);
> BUG_ON(!dl_se);
> p = dl_task_of(dl_se);
> - set_next_task_dl(rq, p, true);
> +
> + return p;
> +}
> +
> +static struct task_struct *pick_next_task_dl(struct rq *rq)
> +{
> + struct task_struct *p;
> +
> + p = pick_task_dl(rq);
> + if (p)
> + set_next_task_dl(rq, p, true);
> +
> return p;
> }
>
> @@ -2551,6 +2562,7 @@ DEFINE_SCHED_CLASS(dl) = {
>
> #ifdef CONFIG_SMP
> .balance = balance_dl,
> + .pick_task = pick_task_dl,
> .select_task_rq = select_task_rq_dl,
> .migrate_task_rq = migrate_task_rq_dl,
> .set_cpus_allowed = set_cpus_allowed_dl,
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 52ddfec7cea6..12cf068eeec8 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4459,7 +4459,7 @@ pick_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *curr)
> * Avoid running the skip buddy, if running something else can
> * be done without getting too unfair.
> */
> - if (cfs_rq->skip == se) {
> + if (cfs_rq->skip && cfs_rq->skip == se) {
> struct sched_entity *second;
>
> if (se == curr) {
> @@ -7017,6 +7017,35 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
> set_last_buddy(se);
> }
>
> +#ifdef CONFIG_SMP
> +static struct task_struct *pick_task_fair(struct rq *rq)
> +{
> + struct cfs_rq *cfs_rq = &rq->cfs;
> + struct sched_entity *se;
> +
> + if (!cfs_rq->nr_running)
> + return NULL;
> +
> + do {
> + struct sched_entity *curr = cfs_rq->curr;
> +
> + se = pick_next_entity(cfs_rq, NULL);
Calling pick_next_entity clears buddies. This is fine without
coresched because the se will be the next one. But calling
pick_task_fair doesn't mean that the se will be used
> +
> + if (curr) {
> + if (se && curr->on_rq)
> + update_curr(cfs_rq);
> +
Shouldn't you check if cfs_rq is throttled ?
> + if (!se || entity_before(curr, se))
> + se = curr;
> + }
> +
> + cfs_rq = group_cfs_rq(se);
> + } while (cfs_rq);
> +
> + return task_of(se);
> +}
> +#endif
> +
> struct task_struct *
> pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
> {
> @@ -11219,6 +11248,7 @@ DEFINE_SCHED_CLASS(fair) = {
>
> #ifdef CONFIG_SMP
> .balance = balance_fair,
> + .pick_task = pick_task_fair,
> .select_task_rq = select_task_rq_fair,
> .migrate_task_rq = migrate_task_rq_fair,
>
> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> index 50e128b899c4..33864193a2f9 100644
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -406,6 +406,13 @@ static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool fir
> schedstat_inc(rq->sched_goidle);
> }
>
> +#ifdef CONFIG_SMP
> +static struct task_struct *pick_task_idle(struct rq *rq)
> +{
> + return rq->idle;
> +}
> +#endif
> +
> struct task_struct *pick_next_task_idle(struct rq *rq)
> {
> struct task_struct *next = rq->idle;
> @@ -473,6 +480,7 @@ DEFINE_SCHED_CLASS(idle) = {
>
> #ifdef CONFIG_SMP
> .balance = balance_idle,
> + .pick_task = pick_task_idle,
> .select_task_rq = select_task_rq_idle,
> .set_cpus_allowed = set_cpus_allowed_common,
> #endif
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index a6f9d132c24f..a0e245b0c4bd 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1626,7 +1626,7 @@ static struct task_struct *_pick_next_task_rt(struct rq *rq)
> return rt_task_of(rt_se);
> }
>
> -static struct task_struct *pick_next_task_rt(struct rq *rq)
> +static struct task_struct *pick_task_rt(struct rq *rq)
> {
> struct task_struct *p;
>
> @@ -1634,7 +1634,17 @@ static struct task_struct *pick_next_task_rt(struct rq *rq)
> return NULL;
>
> p = _pick_next_task_rt(rq);
> - set_next_task_rt(rq, p, true);
> +
> + return p;
> +}
> +
> +static struct task_struct *pick_next_task_rt(struct rq *rq)
> +{
> + struct task_struct *p = pick_task_rt(rq);
> +
> + if (p)
> + set_next_task_rt(rq, p, true);
> +
> return p;
> }
>
> @@ -2483,6 +2493,7 @@ DEFINE_SCHED_CLASS(rt) = {
>
> #ifdef CONFIG_SMP
> .balance = balance_rt,
> + .pick_task = pick_task_rt,
> .select_task_rq = select_task_rq_rt,
> .set_cpus_allowed = set_cpus_allowed_common,
> .rq_online = rq_online_rt,
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index f794c9337047..5a0dd2b312aa 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1839,6 +1839,9 @@ struct sched_class {
> #ifdef CONFIG_SMP
> int (*balance)(struct rq *rq, struct task_struct *prev, struct rq_flags *rf);
> int (*select_task_rq)(struct task_struct *p, int task_cpu, int flags);
> +
> + struct task_struct * (*pick_task)(struct rq *rq);
> +
> void (*migrate_task_rq)(struct task_struct *p, int new_cpu);
>
> void (*task_woken)(struct rq *this_rq, struct task_struct *task);
> diff --git a/kernel/sched/stop_task.c b/kernel/sched/stop_task.c
> index 55f39125c0e1..f988ebe3febb 100644
> --- a/kernel/sched/stop_task.c
> +++ b/kernel/sched/stop_task.c
> @@ -34,15 +34,24 @@ static void set_next_task_stop(struct rq *rq, struct task_struct *stop, bool fir
> stop->se.exec_start = rq_clock_task(rq);
> }
>
> -static struct task_struct *pick_next_task_stop(struct rq *rq)
> +static struct task_struct *pick_task_stop(struct rq *rq)
> {
> if (!sched_stop_runnable(rq))
> return NULL;
>
> - set_next_task_stop(rq, rq->stop, true);
> return rq->stop;
> }
>
> +static struct task_struct *pick_next_task_stop(struct rq *rq)
> +{
> + struct task_struct *p = pick_task_stop(rq);
> +
> + if (p)
> + set_next_task_stop(rq, p, true);
> +
> + return p;
> +}
> +
> static void
> enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
> {
> @@ -123,6 +132,7 @@ DEFINE_SCHED_CLASS(stop) = {
>
> #ifdef CONFIG_SMP
> .balance = balance_stop,
> + .pick_task = pick_task_stop,
> .select_task_rq = select_task_rq_stop,
> .set_cpus_allowed = set_cpus_allowed_common,
> #endif
> --
> 2.29.2.299.gdc1121823c-goog
>
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