linux-kernel - Re: [PATCH AUTOSEL 5.15 11/12] x86/barrier: Do not serialize MSR accesses on AMD

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Message-ID: <Z0oxuu/AASgIOkTa@duo.ucw.cz>
Date: Fri, 29 Nov 2024 22:27:22 +0100
From: Pavel Machek <pavel@...x.de>
To: Sasha Levin <sashal@...nel.org>
Cc: Pavel Machek <pavel@...x.de>, Borislav Petkov <bp@...en8.de>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
	x86@...nel.org, puwen@...on.cn, seanjc@...gle.com,
	kim.phillips@....com, jmattson@...gle.com, babu.moger@....com,
	peterz@...radead.org, rick.p.edgecombe@...el.com, brgerst@...il.com,
	ashok.raj@...el.com, mjguzik@...il.com, jpoimboe@...nel.org,
	nik.borisov@...e.com, aik@....com, vegard.nossum@...cle.com,
	daniel.sneddon@...ux.intel.com, acdunlap@...gle.com,
	Erwan Velu <erwanaliasr1@...il.com>
Subject: Re: [PATCH AUTOSEL 5.15 11/12] x86/barrier: Do not serialize MSR
 accesses on AMD

Hi!

> > >   - Serious issues as reported by a user of a distribution kernel may also
> > >     be considered if they fix a notable performance or interactivity issue.
> > > 
> > > It sounds like what's going on here, no?
> > 
> > Is it? I'd not expect this to be visible in anything but
> > microbenchmarks. Do you have user reports hitting this?
> > 
> > It is not like this makes kernel build 10% slower, is it?
> 
> On Fri, Nov 29, 2024 at 10:30:11AM +0100, Erwan Velu wrote:
> > This patch greatly impacts servers on production with AMD systems that
> > have lasted since 5.11, having it backported really improves systems
> > performance.
> > Since this patch, I can share that our database team is no longer
> > paged during the night, that's a real noticeable impact.

Ok, looks like I misjudged the performance impact, sorry for the
noise.

Best regards,
								Pavel

-- 
DENX Software Engineering GmbH,        Managing Director: Erika Unter
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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