Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <1559178307-6835-1-git-send-email-wanpengli@tencent.com> <20190610143420.GA6594@flask>
In-Reply-To: <20190610143420.GA6594@flask>
From:   Wanpeng Li <kernellwp@gmail.com>
Date:   Tue, 11 Jun 2019 18:26:43 +0800
Message-ID: <CANRm+CwgE5d0hQif0Rj-=q-orxMpSZq+tKLvrkZuatmatYxjWg@mail.gmail.com>
Subject: Re: [PATCH v3 0/3] KVM: Yield to IPI target if necessary
To:     =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>
Cc:     LKML <linux-kernel@vger.kernel.org>, kvm <kvm@vger.kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, 10 Jun 2019 at 22:34, Radim Kr=C4=8Dm=C3=A1=C5=99 <rkrcmar@redhat.c=
om> 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