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

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Date:	Mon, 07 May 2012 18:50:05 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.com>
CC:	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>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.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 05:36 PM, Avi Kivity wrote:
> On 05/07/2012 01:58 PM, Raghavendra K T wrote:
>> On 05/07/2012 02:02 PM, Avi Kivity wrote:
>>> On 05/07/2012 11:29 AM, Ingo Molnar wrote:
>>>> This is looking pretty good and complete now - any objections
>>>> from anyone to trying this out in a separate x86 topic tree?
>>>
>>> No objections, instead an
>>>
>>> Acked-by: Avi Kivity<avi@...hat.com>
>>>
[...]
>>
>> (Less is better. Below is time elapsed in sec for x86_64_defconfig
>> (3+3 runs)).
>>
>>           BASE                    BASE+patch            %improvement
>>           mean (sd)               mean (sd)
>> case 1x:     66.0566 (74.0304)      61.3233 (68.8299)     7.16552
>> case 2x:     1253.2 (1795.74)      131.606 (137.358)     89.4984
>> case 3x:     3431.04 (5297.26)      134.964 (149.861)     96.0664
>>
>
> You're calculating the improvement incorrectly.  In the last case, it's
> not 96%, rather it's 2400% (25x).  Similarly the second case is about
> 900% faster.
>

You are right,
my %improvement was intended to be like
if
1) base takes 100 sec ==> patch takes 93 sec
2) base takes 100 sec ==> patch takes 11 sec
3) base takes 100 sec ==> patch takes 4 sec

The above is more confusing (and incorrect!).

Better is what you told which boils to 10x and 25x improvement in case
2 and case 3. And IMO, this *really* gives the feeling of magnitude of
improvement with patches.

I ll change script to report that way :).

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