linux-kernel - Re: [PATCH v10 18/19] pvqspinlock, x86: Enable PV qspinlock PV for KVM

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Date:	Thu, 08 May 2014 13:54:07 -0400
From:	Waiman Long <waiman.long@...com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-arch@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	xen-devel@...ts.xenproject.org, kvm@...r.kernel.org,
	Paolo Bonzini <paolo.bonzini@...il.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Gleb Natapov <gleb@...hat.com>,
	Scott J Norton <scott.norton@...com>,
	Chegu Vinod <chegu_vinod@...com>
Subject: Re: [PATCH v10 18/19] pvqspinlock, x86: Enable PV qspinlock PV for
 KVM

On 05/07/2014 03:07 PM, Konrad Rzeszutek Wilk wrote:
>> Raghavendra KT had done some performance testing on this patch with
>> the following results:
>>
>> Overall we are seeing good improvement for pv-unfair version.
>>
>> System: 32 cpu sandybridge with HT on (4 node with 32 GB each)
>> Guest : 8GB with 16 vcpu/VM.
>> Average was taken over 8-10 data points.
>>
>> Base = 3.15-rc2  with PRAVIRT_SPINLOCK = y
>>
>> A = 3.15-rc2 + qspinlock v9 patch with QUEUE_SPINLOCK = y
>> PRAVIRT_SPINLOCK = y PARAVIRT_UNFAIR_LOCKS = y (unfair lock)
>>
>> B =  3.15-rc2 + qspinlock v9 patch with QUEUE_SPINLOCK = y
>> PRAVIRT_SPINLOCK = n PARAVIRT_UNFAIR_LOCKS = n
>> (queue spinlock without paravirt)
>>
>> C = 3.15-rc2 + qspinlock v9 patch with  QUEUE_SPINLOCK = y
>> PRAVIRT_SPINLOCK = y  PARAVIRT_UNFAIR_LOCKS = n
>> (queue spinlock with paravirt)
> Could you do s/PRAVIRT/PARAVIRT/ please?
>

Sorry for the typo, I didn't check the text carefully enough when I 
cut-and-paste it from Raghavendra's email.

>> Ebizzy %improvements
>> ====================
>> overcommit  A            B            C
>> 0.5x     4.4265        2.0611       1.5824
>> 1.0x     0.9015       -7.7828       4.5443
>> 1.5x    46.1162       -2.9845      -3.5046
>> 2.0x    99.8150       -2.7116       4.7461
> Considering B sucks

Yes, I don't expect the plain qspinlock code will perform well in a 
guest without either unfair or pvspinlock support.

-Longman
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