linux-kernel - Re: [PATCH v3 1/2] cpu/smt: add a notifier to notify the SMT changes

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Date:   Wed, 29 Mar 2023 10:50:23 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Yang, WenYou" <WenYou.Yang@....com>
Cc:     "Deucher, Alexander" <Alexander.Deucher@....com>,
        "Koenig, Christian" <Christian.Koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        "Quan, Evan" <Evan.Quan@....com>,
        "Limonciello, Mario" <Mario.Limonciello@....com>, bp@...en8.de,
        "jpoimboe@...nel.org" <jpoimboe@...nel.org>,
        "Phillips, Kim" <kim.phillips@....com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "Yuan, Perry" <Perry.Yuan@....com>,
        "Liang, Richard qi" <Richardqi.Liang@....com>,
        "Li, Ying" <YING.LI@....com>, "Liu, Kun" <Kun.Liu2@....com>,
        "gpiccoli@...lia.com" <gpiccoli@...lia.com>,
        "amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] cpu/smt: add a notifier to notify the SMT changes

On Wed, Mar 29, 2023 at 07:23:29AM +0000, Yang, WenYou wrote:
> [AMD Official Use Only - General]

^^^ that has no business being in a public email.

> Hi Peter,
> 
> Thank you for your review.
> 
> The purpose of the patch set is to improve the performance when playing game for some AMD APUs with SMT enabled/disabled.
> 
> When change the SMT state on the fly through " echo on/off > /sys/devices/system/cpu/smt/control", the kernel needs to send a message to notify PMFW to adjust a variable's value, which impacts the performance.

When top posting I normally ignore the email. When not wrapping email I
typically get cranky. You 'win' *3* 'I cannot use email' trophies in a
singly try. Surely AMD has a HOWTO somewhere you can read?

So what do you want to have happen when someone goes and manually
offlines all the SMT siblings using /sys/devices/system/cpu/cpu*/online
?

I'm thinking that wants the same PMFW (whatever the heck that is)
notification change done, right?

If the answer is "yes", then your patch does not meet the goals and is
inadequate.