Message-ID: <5175A29E.1070704@redhat.com>
Date: Mon, 22 Apr 2013 16:50:38 -0400
From: Rik van Riel <riel@redhat.com>
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To: Peter Zijlstra <peterz@infradead.org>
CC: Jiannan Ouyang <ouyang@cs.pitt.edu>, LKML <linux-kernel@vger.kernel.org>,
        Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
        Avi Kivity <avi.kivity@gmail.com>, Gleb Natapov <gleb@redhat.com>,
        Ingo Molnar <mingo@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>,
        Srikar <srikar@linux.vnet.ibm.com>, "H. Peter Anvin" <hpa@zytor.com>,
        "Nikunj A. Dadhania" <nikunj@linux.vnet.ibm.com>,
        KVM <kvm@vger.kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
        Chegu Vinod <chegu_vinod@hp.com>,
        "Andrew M. Theurer" <habanero@linux.vnet.ibm.com>,
        Srivatsa Vaddagiri <srivatsa.vaddagiri@gmail.com>,
        Andrew Jones <drjones@redhat.com>, Karen Noel <knoel@redhat.com>
Subject: Re: Preemptable Ticket Spinlock
References: <CAJocwccu5QQyuKRvgNyPSFz2K_rzCW419W9-XdSUYOL7+KqQKg@mail.gmail.com>  <51745650.9050204@redhat.com> <1366631460.4443.3.camel@laptop>  <51753289.70406@redhat.com> <1366660147.6454.6.camel@laptop>  <517595FA.800@redhat.com> <1366661294.6454.18.camel@laptop>  <51759E43.2080003@redhat.com> <1366663475.8337.10.camel@laptop> <1366663714.8337.12.camel@laptop>
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On 04/22/2013 04:48 PM, Peter Zijlstra wrote:

> Hmm.. it looked like under light overcommit the paravirt ticket lock
> still had some gain (~10%) and of course it brings the fairness thing
> which is always good.
>
> I can only imagine the mess unfair + vcpu preemption can bring to guest
> tasks.

If you think unfairness + vcpu preemption is bad, you haven't
tried full fairness + vcpu preemption :)

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