linux-kernel - Re: [PATCH v5 0/2] KVM: x86: Include host suspended time in steal time

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Message-ID: <CABCjUKBfCe_iAU-9THb=OENFuEE5JMkSN0yPpHQsVo-S6WYViw@mail.gmail.com>
Date: Tue, 8 Apr 2025 10:36:10 +0900
From: Suleiman Souhlal <suleiman@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.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, 
	"H. Peter Anvin" <hpa@...or.com>, Chao Gao <chao.gao@...el.com>, 
	David Woodhouse <dwmw2@...radead.org>, Sergey Senozhatsky <senozhatsky@...omium.org>, 
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	ssouhlal@...ebsd.org
Subject: Re: [PATCH v5 0/2] KVM: x86: Include host suspended time in steal time

On Tue, Mar 25, 2025 at 1:13 PM Suleiman Souhlal <suleiman@...gle.com> wrote:
>
> This series makes it so that the time that the host is suspended is
> included in guests' steal time.

Friendly ping.

-- Suleiman

>
> When the host resumes from a suspend, the guest thinks any task
> that was running during the suspend ran for a long time, even though
> the effective run time was much shorter, which can end up having
> negative effects with scheduling.
>
> To mitigate this issue, we include the time that the host was
> suspended in steal time, which lets the guest can subtract the
> duration from the tasks' runtime.
>
> In addition, we make the guest TSC behavior consistent whether the
> host TSC went backwards or not.
>
> v5:
> - Fix grammar mistakes in commit message.
>
> v4: https://lore.kernel.org/kvm/20250221053927.486476-1-suleiman@google.com/T/
> - Advance guest TSC on suspends where host TSC goes backwards.
> - Block vCPUs from running until resume notifier.
> - Move suspend duration accounting out of machine-independent kvm to
>   x86.
> - Merge code and documentation patches.
> - Reworded documentation.
>
> v3: https://lore.kernel.org/kvm/Z5AB-6bLRNLle27G@google.com/T/
> - Use PM notifier instead of syscore ops (kvm_suspend()/kvm_resume()),
>   because the latter doesn't get called on shallow suspend.
> - Don't call function under UACCESS.
> - Whitespace.
>
> v2: https://lore.kernel.org/lkml/20241118043745.1857272-1-suleiman@google.com/
> - Accumulate suspend time at machine-independent kvm layer and track per-VCPU
>   instead of per-VM.
> - Document changes.
>
> v1: https://lore.kernel.org/kvm/20240710074410.770409-1-suleiman@google.com/
>
> Suleiman Souhlal (2):
>   KVM: x86: Advance guest TSC after deep suspend.
>   KVM: x86: Include host suspended time in steal time
>
>  Documentation/virt/kvm/x86/msr.rst | 10 +++-
>  arch/x86/include/asm/kvm_host.h    |  7 +++
>  arch/x86/kvm/x86.c                 | 84 +++++++++++++++++++++++++++++-
>  3 files changed, 98 insertions(+), 3 deletions(-)
>
> --
> 2.49.0.395.g12beb8f557-goog
>