linux-kernel - Re: [PATCH v2 0/3] KVM: x86: Include host suspended time in steal time.

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Message-ID: <ZvQWIsRlrmHsB3DB@google.com>
Date: Wed, 25 Sep 2024 06:54:42 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Suleiman Souhlal <suleiman@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, 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>, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, ssouhlal@...ebsd.org, 
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH v2 0/3] KVM: x86: Include host suspended time in steal time.

+David W for his input.

On Tue, Aug 20, 2024, Suleiman Souhlal wrote:
> This series makes it so that the time that the host is suspended is
> included in guests' steal time.
> 
> 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. This can be particularly noticeable
> if the guest task was RT, as it can end up getting throttled for a
> long time.
> 
> 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.
> 
> (v1 was at https://lore.kernel.org/kvm/20240710074410.770409-1-suleiman@google.com/)
> 
> v1 -> v2:
> - Accumulate suspend time at machine-independent kvm layer and track per-VCPU
>   instead of per-VM.
> - Document changes.
> 
> Suleiman Souhlal (3):
>   KVM: Introduce kvm_total_suspend_ns().
>   KVM: x86: Include host suspended time in steal time.
>   KVM: x86: Document host suspend being included in steal time.
> 
>  Documentation/virt/kvm/x86/msr.rst |  6 ++++--
>  arch/x86/include/asm/kvm_host.h    |  1 +
>  arch/x86/kvm/x86.c                 | 11 ++++++++++-
>  include/linux/kvm_host.h           |  2 ++
>  virt/kvm/kvm_main.c                | 13 +++++++++++++
>  5 files changed, 30 insertions(+), 3 deletions(-)
> 
> -- 
> 2.46.0.184.g6999bdac58-goog
>