linux-kernel - Re: [PATCH 1/6] x86/microcode: Introduce staging option to reduce late-loading latency

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Message-ID: <20250218113634.GGZ7RwwkrrXADX0eRo@fat_crate.local>
Date: Tue, 18 Feb 2025 12:36:34 +0100
From: Borislav Petkov <bp@...en8.de>
To: "Chang S. Bae" <chang.seok.bae@...el.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, tglx@...utronix.de,
	mingo@...hat.com, dave.hansen@...ux.intel.com
Subject: Re: [PATCH 1/6] x86/microcode: Introduce staging option to reduce
 late-loading latency

On Mon, Feb 17, 2025 at 11:51:28PM -0800, Chang S. Bae wrote:
> On 2/17/2025 5:33 AM, Borislav Petkov wrote:
> > 
> > Why are you even touching this function instead of doing the staging in the
> > beginning of load_late_stop_cpus()?
> 
> I thought staging is logically distinguishable.

What does that even mean?

> While load_late_stop_cpus() currently performs loading when CPUs are
> _stopped_,

Not entirely - it does preparatory work and then stops the CPUs. Staging could
be part of that prep work.

> staging occurs on a non-critical path and remains interruptible.

So if you really wanna do that and be really "free", then you should do it
outside of load_late_locked() because that runs with the hotplug lock taken.

But then the only thing that matters is, when *exactly* you should stage. If
->request_microcode_fw() fails, staging would be unnecessary work.

So instead of trying to too hard, just stick the staging at the beginning of
load_late_stop_cpus() and be done with it.

Also, if you want to send a patch, don't send it from a mail client which will
mangle it so that it is inapplicable and no one can play with it.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette