linux-kernel - Re: [PATCH -tip 02/32] sched: Introduce sched_class::pick

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Message-ID: <025bb649-89c5-a353-1434-2da725adffd9@gmail.com>
Date:   Fri, 20 Nov 2020 10:56:09 +1100
From:   "Singh, Balbir" <bsingharora@...il.com>
To:     "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        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
Cc:     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@...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 18/11/20 10:19 am, Joel Fernandes (Google) 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.
> 

The change makes sense, a small suggestion below

> 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);
> +
> +		if (curr) {
> +			if (se && curr->on_rq)
> +				update_curr(cfs_rq);
> +
> +			if (!se || entity_before(curr, se))
> +				se = curr;
> +		}

Do we want to optimize this a bit 

if (curr) {
	if (!se || entity_before(curr, se))
		se = curr;

	if ((se != curr) && curr->on_rq)
		update_curr(cfs_rq);

}

Balbir