linux-kernel - Re: [PATCH v16 12/13] x86/tsc: Switch to native sched clock

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Message-ID: <20250107193752.GHZ32CkNhBJkx45Ug4@fat_crate.local>
Date: Tue, 7 Jan 2025 20:37:52 +0100
From: Borislav Petkov <bp@...en8.de>
To: Nikunj A Dadhania <nikunj@....com>
Cc: linux-kernel@...r.kernel.org, thomas.lendacky@....com, x86@...nel.org,
	kvm@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
	dave.hansen@...ux.intel.com, pgonda@...gle.com, seanjc@...gle.com,
	pbonzini@...hat.com, francescolavra.fl@...il.com,
	Alexey Makhalov <alexey.makhalov@...adcom.com>,
	Juergen Gross <jgross@...e.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [PATCH v16 12/13] x86/tsc: Switch to native sched clock

On Mon, Jan 06, 2025 at 06:16:32PM +0530, Nikunj A Dadhania wrote:
> Although the kernel switches over to stable TSC clocksource instead of
> PV clocksource, the scheduler still keeps on using PV clocks as the
> sched clock source. This is because KVM, Xen and VMWare, switch the
> paravirt sched clock handler in their init routines. HyperV is the
> only PV clock source that checks if the platform provides an invariant
> TSC and does not switch to PV sched clock.

So this below looks like some desperate hackery. Are you doing this because
kvm_sched_clock_init() does

	paravirt_set_sched_clock(kvm_sched_clock_read);

?

If so, why don't you simply prevent that on STSC guests?

-- 
Regards/Gruss,
    Boris.

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