linux-kernel - Re: [PATCH v2 02/12] sched/deadline: Less agressive dl

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Message-ID: <aInp78zC_WwVW6yd@jlelli-thinkpadt14gen4.remote.csb>
Date: Wed, 30 Jul 2025 11:46:23 +0200
From: Juri Lelli <juri.lelli@...hat.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com,
	vincent.guittot@...aro.org, dietmar.eggemann@....com,
	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
	vschneid@...hat.com, clm@...a.com, linux-kernel@...r.kernel.org,
	linux-m68k <linux-m68k@...ts.linux-m68k.org>
Subject: Re: [PATCH v2 02/12] sched/deadline: Less agressive dl_server
 handling

Hello,

On 30/07/25 11:34, Geert Uytterhoeven wrote:
> Hi Peter,

Apologies for interjecting.

> On Wed, 2 Jul 2025 at 14:19, Peter Zijlstra <peterz@...radead.org> wrote:
> > Chris reported that commit 5f6bd380c7bd ("sched/rt: Remove default
> > bandwidth control") caused a significant dip in his favourite
> > benchmark of the day. Simply disabling dl_server cured things.
> >
> > His workload hammers the 0->1, 1->0 transitions, and the
> > dl_server_{start,stop}() overhead kills it -- fairly obviously a bad
> > idea in hind sight and all that.
> >
> > Change things around to only disable the dl_server when there has not
> > been a fair task around for a whole period. Since the default period
> > is 1 second, this ensures the benchmark never trips this, overhead
> > gone.
> >
> > Fixes: 557a6bfc662c ("sched/fair: Add trivial fair server")
> > Reported-by: Chris Mason <clm@...a.com>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > Link: https://lkml.kernel.org/r/20250520101727.507378961@infradead.org
> 
> Thanks for your patch, which is now commit cccb45d7c4295bbf
> ("sched/deadline: Less agressive dl_server handling") upstream.
> 
> This commit causes
> 
>     sched: DL replenish lagged too much
> 
> to be printed after full user-space (Debian) start-up on m68k
> (atari_defconfig running on ARAnyM).  Reverting this commit and fixing
> the small conflict gets rid of the message.

Does
https://lore.kernel.org/lkml/20250615131129.954975-1-kuyo.chang@mediatek.com/
help already (w/o the revert)?

Best,
Juri