linux-kernel - Re: [PATCH 16/16] x86/kvmclock: Use TSC for sched

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Message-ID: <Z60m6NiOlCmy4-q0@google.com>
Date: Wed, 12 Feb 2025 14:55:36 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Michael Kelley <mhklinux@...look.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, "x86@...nel.org" <x86@...nel.org>, 
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Juergen Gross <jgross@...e.com>, 
	"K. Y. Srinivasan" <kys@...rosoft.com>, Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>, 
	Dexuan Cui <decui@...rosoft.com>, Ajay Kaher <ajay.kaher@...adcom.com>, 
	Jan Kiszka <jan.kiszka@...mens.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>, 
	"virtualization@...ts.linux.dev" <virtualization@...ts.linux.dev>, 
	"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>, 
	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>, Nikunj A Dadhania <nikunj@....com>, 
	Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH 16/16] x86/kvmclock: Use TSC for sched_clock if it's
 constant and non-stop

On Wed, Feb 12, 2025, Michael Kelley wrote:
> From: Sean Christopherson <seanjc@...gle.com> Sent: Monday, February 10, 2025 8:22 AM
> > On Sat, Feb 08, 2025, Michael Kelley wrote:
> > > But I would be good with some restructuring so that setting the sched clock
> > > save/restore hooks is more closely tied to the sched clock choice,
> > 
> > Yeah, this is the intent of my ranting.  After the dust settles, the code can
> > look like this.
> 
> I'm good with what you are proposing. And if you want, there's no real need
> for hv_ref_counter_at_suspend and hv_save/restore_sched_clock_state()
> to be in the #ifdef sequence since the code has no architecture dependencies.

Right, but because they will be local/static and there are no users outside of
x86, the compiler will complain about unused variables/functions on other
architectures.