linux-kernel - Re: [PATCH v3 0/3] KVM: Yield to IPI target if necessary

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Message-ID: <CANRm+CwgE5d0hQif0Rj-=q-orxMpSZq+tKLvrkZuatmatYxjWg@mail.gmail.com>
Date:   Tue, 11 Jun 2019 18:26:43 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Radim Krčmář <rkrcmar@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v3 0/3] KVM: Yield to IPI target if necessary

On Mon, 10 Jun 2019 at 22:34, Radim Krčmář <rkrcmar@...hat.com> wrote:
>
> 2019-05-30 09:05+0800, Wanpeng Li:
> > The idea is from Xen, when sending a call-function IPI-many to vCPUs,
> > yield if any of the IPI target vCPUs was preempted. 17% performance
> > increasement of ebizzy benchmark can be observed in an over-subscribe
> > environment. (w/ kvm-pv-tlb disabled, testing TLB flush call-function
> > IPI-many since call-function is not easy to be trigged by userspace
> > workload).
>
> Have you checked if we could gain performance by having the yield as an
> extension to our PV IPI call?

It will extend irq disabled time in __send_ipi_mask(). In addition,
sched yield can be used to optimize other synchronization primitives
in guest I think.

Regards,
Wanpeng Li