Message-ID: <4FA8E272.5040307@redhat.com>
Date: Tue, 08 May 2012 12:08:02 +0300
From: Avi Kivity <avi@redhat.com>
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To: Jeremy Fitzhardinge <jeremy@goop.org>
CC: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
        Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
        Ingo Molnar <mingo@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@suse.de>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Marcelo Tosatti <mtosatti@redhat.com>, X86 <x86@kernel.org>,
        Gleb Natapov <gleb@redhat.com>, Ingo Molnar <mingo@redhat.com>,
        Attilio Rao <attilio.rao@citrix.com>,
        Virtualization <virtualization@lists.linux-foundation.org>,
        Xen Devel <xen-devel@lists.xensource.com>, linux-doc@vger.kernel.org,
        KVM <kvm@vger.kernel.org>, Andi Kleen <andi@firstfloor.org>,
        Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
        Stephan Diestelhorst <stephan.diestelhorst@amd.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH RFC V8 0/17] Paravirtualized ticket spinlocks
References: <20120502100610.13206.40.sendpatchset@codeblue.in.ibm.com> <20120507082928.GI16608@gmail.com> <4FA7888F.80505@redhat.com> <4FA7AAD8.6050003@linux.vnet.ibm.com> <4FA7BABA.4040700@redhat.com> <4FA7CC05.50808@linux.vnet.ibm.com> <4FA7CCA2.4030408@redhat.com> <4FA7D06B.60005@linux.vnet.ibm.com> <20120507134611.GB5533@linux.vnet.ibm.com> <4FA7D2E5.1020607@redhat.com> <4FA8579C.3000205@goop.org>
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On 05/08/2012 02:15 AM, Jeremy Fitzhardinge wrote:
> On 05/07/2012 06:49 AM, Avi Kivity wrote:
> > On 05/07/2012 04:46 PM, Srivatsa Vaddagiri wrote:
> >> * Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> [2012-05-07 19:08:51]:
> >>
> >>> I 'll get hold of a PLE mc  and come up with the numbers soon. but I
> >>> 'll expect the improvement around 1-3% as it was in last version.
> >> Deferring preemption (when vcpu is holding lock) may give us better than 1-3% 
> >> results on PLE hardware. Something worth trying IMHO.
> > Is the improvement so low, because PLE is interfering with the patch, or
> > because PLE already does a good job?
>
> How does PLE help with ticket scheduling on unlock?  I thought it would
> just help with the actual spin loops.

PLE yields to up a random vcpu, hoping it is the lock holder.  This
patchset wakes up the right vcpu.  For small vcpu counts the difference
is a few bad wakeups (and even a bad wakeup sometimes works, since it
can put the spinner to sleep for a bit).  I expect that large vcpu
counts would show a greater difference.

-- 
error compiling committee.c: too many arguments to function

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