linux-kernel - Re: [PATCH 11/15] sched/eevdf: Better handle mixed slice length

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Date:   Sat, 10 Jun 2023 14:34:04 +0800
From:   Chen Yu <yu.c.chen@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     <mingo@...nel.org>, <vincent.guittot@...aro.org>,
        <linux-kernel@...r.kernel.org>, <juri.lelli@...hat.com>,
        <dietmar.eggemann@....com>, <rostedt@...dmis.org>,
        <bsegall@...gle.com>, <mgorman@...e.de>, <bristot@...hat.com>,
        <corbet@....net>, <qyousef@...alina.io>, <chris.hyser@...cle.com>,
        <patrick.bellasi@...bug.net>, <pjt@...gle.com>, <pavel@....cz>,
        <qperret@...gle.com>, <tim.c.chen@...ux.intel.com>,
        <joshdon@...gle.com>, <timj@....org>, <kprateek.nayak@....com>,
        <youssefesmat@...omium.org>, <joel@...lfernandes.org>,
        <efault@....de>, <tglx@...utronix.de>
Subject: Re: [PATCH 11/15] sched/eevdf: Better handle mixed slice length

On 2023-05-31 at 13:58:50 +0200, Peter Zijlstra wrote:
> In the case where (due to latency-nice) there are different request
> sizes in the tree, the smaller requests tend to be dominated by the
> larger. Also note how the EEVDF lag limits are based on r_max.
> 
> Therefore; add a heuristic that for the mixed request size case, moves
> smaller requests to placement strategy #2 which ensures they're
> immidiately eligible and and due to their smaller (virtual) deadline
> will cause preemption.
> 
> NOTE: this relies on update_entity_lag() to impose lag limits above
> a single slice.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  kernel/sched/fair.c     |   30 ++++++++++++++++++++++++++++++
>  kernel/sched/features.h |    1 +
>  kernel/sched/sched.h    |    1 +
>  3 files changed, 32 insertions(+)
> 
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -642,6 +642,7 @@ avg_vruntime_add(struct cfs_rq *cfs_rq,
>  	s64 key = entity_key(cfs_rq, se);
>  
>  	cfs_rq->avg_vruntime += key * weight;
> +	cfs_rq->avg_slice += se->slice * weight;
>  	cfs_rq->avg_load += weight;
>  }
>  
> @@ -652,6 +653,7 @@ avg_vruntime_sub(struct cfs_rq *cfs_rq,
>  	s64 key = entity_key(cfs_rq, se);
>  
>  	cfs_rq->avg_vruntime -= key * weight;
> +	cfs_rq->avg_slice -= se->slice * weight;
>  	cfs_rq->avg_load -= weight;
>  }
>  
> @@ -4908,6 +4910,21 @@ static inline void update_misfit_status(
>  
>  #endif /* CONFIG_SMP */
>  
> +static inline bool
> +entity_has_slept(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
> +{
> +	u64 now;
> +
> +	if (!(flags & ENQUEUE_WAKEUP))
> +		return false;
> +
> +	if (flags & ENQUEUE_MIGRATED)
> +		return true;
> +
> +	now = rq_clock_task(rq_of(cfs_rq));
> +	return (s64)(se->exec_start - now) >= se->slice;
> +}
A minor question, should it be now - se->exec_start ?
(se->exec_start - now) is always negetive on local wakeup?

thanks,
Chenyu