linux-kernel - Re: EEVDF regression still exists

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Message-ID: <52515bfa-4520-4eb3-80c9-eb1ee0e64ba8@amd.com>
Date: Fri, 2 May 2025 12:38:43 +0530
From: "Sapkal, Swapnil" <swapnil.sapkal@....com>
To: Peter Zijlstra <peterz@...radead.org>, Cristian Prundeanu
	<cpru@...zon.com>
CC: K Prateek Nayak <kprateek.nayak@....com>, Hazem Mohamed Abuelfotoh
	<abuehaze@...zon.com>, Ali Saidi <alisaidi@...zon.com>, "Benjamin
 Herrenschmidt" <benh@...nel.crashing.org>, Geoff Blake <blakgeof@...zon.com>,
	Csaba Csoma <csabac@...zon.com>, Bjoern Doebel <doebel@...zon.com>, "Gautham
 Shenoy" <gautham.shenoy@....com>, Joseph Salisbury
	<joseph.salisbury@...cle.com>, Dietmar Eggemann <dietmar.eggemann@....com>,
	Ingo Molnar <mingo@...hat.com>, Linus Torvalds
	<torvalds@...ux-foundation.org>, Borislav Petkov <bp@...en8.de>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
	<linux-tip-commits@...r.kernel.org>, <x86@...nel.org>
Subject: Re: EEVDF regression still exists

Hello Peter,

On 4/30/2025 3:32 PM, Peter Zijlstra wrote:
> On Tue, Apr 29, 2025 at 04:38:17PM -0500, Cristian Prundeanu wrote:
> 
>> [1] https://github.com/aws/repro-collection/blob/main/repros/repro-mysql-EEVDF-regression/results/20250428/README.md
> 
> That 'perf sched stats diff' output is completely broken -- probably
> trying to diff two different schedstat versions isn't working.
> 

Yeah. Will add a check to bail out the diff command if schedstat versions
are not identical.

> Anyway, looking at the two individual reports side by side:
> 
>   - schedule() left the processor idle             -- is up
> 
> vs.
> 
>   - pull_task() count on cpu newly idle            -- is down
>   - load_balance() success count on cpu newly idle -- is down
> 
> Which seem related and would suggest we look at newidle balance. One of
> the things we've seen before is that newidle was affected by the shorter
> slice of EEVDF. But it is also quite possible something changed in the
> load-balancer here.
> 
> Also of note is that .15 seems to have a lower number of 'ttwu() was
> called to wake up on the local cpu' -- which I'm not quite sure how to
> rhyme with the previous observation. The newidle thing seems to suggest
> not enough migrations, while this would suggest too many migrations.
> 
> 
--
Thanks and Regards,
Swapnil