linux-kernel - Re: [PATCH RFC 0/2] kvm: Improving directed yield in PLE handler

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Message-ID: <4FFD69B5.9000401@de.ibm.com>
Date:	Wed, 11 Jul 2012 13:55:33 +0200
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
CC:	Avi Kivity <avi@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, Rik van Riel <riel@...hat.com>,
	S390 <linux-s390@...r.kernel.org>,
	Carsten Otte <cotte@...ibm.com>, KVM <kvm@...r.kernel.org>,
	chegu vinod <chegu_vinod@...com>,
	"Andrew M. Theurer" <habanero@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>, X86 <x86@...nel.org>,
	Gleb Natapov <gleb@...hat.com>, linux390@...ibm.com,
	Srivatsa Vaddagiri <srivatsa.vaddagiri@...il.com>,
	Joerg Roedel <joerg.roedel@....com>,
	Christian Ehrhardt <ehrhardt@...ux.vnet.ibm.com>
Subject: Re: [PATCH RFC 0/2] kvm: Improving directed yield in PLE handler

On 11/07/12 13:51, Raghavendra K T wrote:
>>>> Almost all s390 kernels use diag9c (directed yield to a given guest cpu) for spinlocks, though.
>>>
>>> Perhaps x86 should copy this.
>>
>> See arch/s390/lib/spinlock.c
>> The basic idea is using several heuristics:
>> - loop for a given amount of loops
>> - check if the lock holder is currently scheduled by the hypervisor
>>    (smp_vcpu_scheduled, which uses the sigp sense running instruction)
>>    Dont know if such thing is available for x86. It must be a lot cheaper
>>    than a guest exit to be useful
> 
> Unfortunately we do not have information on lock-holder.

That would be an independent patch and requires guest changes.


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