From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@redhat.com>
Subject: Re: [PATCH RFC V8 0/17] Paravirtualized ticket spinlocks
Date: Mon, 07 May 2012 17:52:56 +0300
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To: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>, Greg Kroah-Hartman <gregkh@suse.de>, KVM <kvm@vger.kernel.org>, linux-doc@vger.kernel.org, Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>, Andi Kleen <andi@firstfloor.org>, "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@kernel.org>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, Xen Devel <xen-devel@lists.xensource.com>, X86 <x86@kernel.org>, Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <a.p.zijlstra@chello.nl>, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>, Thomas Gleixner <tglx@linutronix.de>, Virtualization <virtualization@lists.linux-foundation.org>, LKML <linux-kernel@vger.kernel.org>, Attilio Rao <attilio.rao@citrix.com>, Andrew Morton <akpm@linux-foundation.org>, Linus Torvalds <torvalds@linux-foundation.org>, Stephan Diestelhorst <stephan.diestelhorst@amd.com>
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On 05/07/2012 05:47 PM, Raghavendra K T wrote:
>> Not good.  Solving a problem in software that is already solved by
>> hardware?  It's okay if there are no costs involved, but here we're
>> introducing a new ABI that we'll have to maintain for a long time.
>>
>
>
> Hmm agree that being a step ahead of mighty hardware (and just an
> improvement of 1-3%) is no good for long term (where PLE is future).
>

PLE is the present, not the future.  It was introduced on later Nehalems
and is present on all Westmeres.  Two more processor generations have
passed meanwhile.  The AMD equivalent was also introduced around that
timeframe.

> Having said that, it is hard for me to resist saying :
>  bottleneck is somewhere else on PLE m/c and IMHO answer would be
> combination of paravirt-spinlock + pv-flush-tb.
>
> But I need to come up with good number to argue in favour of the claim.
>
> PS: Nikunj had experimented that pv-flush tlb + paravirt-spinlock is a
> win on PLE where only one of them alone could not prove the benefit.
>

I'd like to see those numbers, then.

Ingo, please hold on the kvm-specific patches, meanwhile.

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