linux-kernel - Re: [PATCH] KVM: Disable wake-affine vCPU process to mitigate lock holder preemption

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Message-ID: <04700afaf68114b5ab329f5a5182e21578c15795.camel@suse.com>
Date:   Thu, 01 Aug 2019 14:57:50 +0200
From:   Dario Faggioli <dfaggioli@...e.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] KVM: Disable wake-affine vCPU process to mitigate lock
 holder preemption

On Tue, 2019-07-30 at 17:33 +0800, Wanpeng Li wrote:
> However, in multiple VMs over-subscribe virtualization scenario, it
> increases 
> the probability to incur vCPU stacking which means that the sibling
> vCPUs from 
> the same VM will be stacked on one pCPU. I test three 80 vCPUs VMs
> running on 
> one 80 pCPUs Skylake server(PLE is supported), the ebizzy score can
> increase 17% 
> after disabling wake-affine for vCPU process. 
> 
Can't we achieve this by removing SD_WAKE_AFFINE from the relevant
scheduling domains? By acting on
/proc/sys/kernel/sched_domain/cpuX/domainY/flags, I mean?

Of course this will impact all tasks, not only KVM vcpus. But if the
host does KVM only anyway...

Regards
-- 
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
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