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

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Date:	Tue, 08 May 2012 10:55:12 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.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 08:22 PM, Avi Kivity wrote:
> 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.
>


Hmm. I think I messed up the fact while saying 1-3% improvement on PLE.

Going by what I had posted in  https://lkml.org/lkml/2012/4/5/73 (with
correct calculation)

   1x  	 70.475 (85.6979) 	63.5033 (72.7041)   15.7%
   2x  	 110.971 (132.829) 	105.099 (128.738)    5.56%	
   3x   	 150.265 (184.766) 	138.341 (172.69)     8.62%


It was around 12% with optimization patch posted separately with that 
(That one Needs more experiment though)

But anyways, I will come up with result for current patch series..

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