linux-kernel - Re: [RFC PATCH 0/1] sched/eevdf: Curb wakeup preemption further

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Message-ID: <8bce19b2-37d9-4722-ba83-0088a4c9fc6a@linux.ibm.com>
Date: Thu, 28 Mar 2024 15:56:27 +0530
From: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
To: K Prateek Nayak <kprateek.nayak@....com>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
        Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira
 <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>, linux-kernel@...r.kernel.org,
        Tobias Huschle <huschle@...ux.ibm.com>,
        Luis Machado <luis.machado@....com>, Chen Yu <yu.c.chen@...el.com>,
        Abel Wu <wuyun.abel@...edance.com>,
        Tianchen Ding
 <dtcccc@...ux.alibaba.com>,
        Youssef Esmat <youssefesmat@...omium.org>,
        Xuewen Yan <xuewen.yan94@...il.com>,
        "Gautham R. Shenoy" <gautham.shenoy@....com>,
        Ingo Molnar
 <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [RFC PATCH 0/1] sched/eevdf: Curb wakeup preemption further

Hi Prateek,

On 25/03/24 11:32, K Prateek Nayak wrote:
> Wakeup preemption problem
> =========================
> 
> With the curr entity's eligibility check, a wakeup preemption is very
> likely when an entity with positive lag joins the runqueue pushing the
> avg_vruntime of the runqueue backwards, making the vruntime of the
> current entity ineligible. This leads to aggressive wakeup preemption
> which was previously guarded by wakeup_granularity_ns in legacy CFS.

Is base_slice_ns not guarding it in EEVDF?

> Below figure depicts one such aggressive preemption scenario with EEVDF:

Thanks and Regards
Madadi Vineeth Reddy