linux-kernel - Re: [tip:sched/eevdf] [sched/fair] e0c2ff903c: phoronix-test-suite.blogbench.Write.final

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Message-ID: <20230816123716.GI980931@hirez.programming.kicks-ass.net>
Date:   Wed, 16 Aug 2023 14:37:16 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mike Galbraith <umgwanakikbuti@...il.com>
Cc:     Chen Yu <yu.c.chen@...el.com>,
        kernel test robot <oliver.sang@...el.com>,
        oe-lkp@...ts.linux.dev, lkp@...el.com,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [tip:sched/eevdf] [sched/fair]  e0c2ff903c:
 phoronix-test-suite.blogbench.Write.final_score -34.8% regression

On Mon, Aug 14, 2023 at 08:32:55PM +0200, Mike Galbraith wrote:

> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -875,6 +875,12 @@ static struct sched_entity *pick_eevdf(s
>  	if (curr && (!curr->on_rq || !entity_eligible(cfs_rq, curr)))
>  		curr = NULL;
>  
> +	/*
> +	 * Once selected, run the task to parity to avoid overscheduling.
> +	 */
> +	if (sched_feat(RUN_TO_PARITY) && curr)
> +		return curr;
> +
>  	while (node) {
>  		struct sched_entity *se = __node_2_se(node);
>  

So I read it wrong last night... but I rather like this idea. But
there's something missing. When curr starts a new slice it should
probably do a full repick and not stick with it.

Let me poke at this a bit.. nice