linux-kernel - Re: [PATCH RFC V8 0/17] Paravirtualized ticket spinlocks

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Message-ID: <4FA7E1C8.7010509@redhat.com>
Date:	Mon, 07 May 2012 17:52:56 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
CC:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Marcelo Tosatti <mtosatti@...hat.com>, X86 <x86@...nel.org>,
	Gleb Natapov <gleb@...hat.com>, Ingo Molnar <mingo@...hat.com>,
	Attilio Rao <attilio.rao@...rix.com>,
	Virtualization <virtualization@...ts.linux-foundation.org>,
	Xen Devel <xen-devel@...ts.xensource.com>,
	linux-doc@...r.kernel.org, KVM <kvm@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Stephan Diestelhorst <stephan.diestelhorst@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH RFC V8 0/17] Paravirtualized ticket spinlocks

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

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