linux-kernel - Re: [PATCH V2 RFC 2/3] kvm: Handle yield_to failure return code for potential undercommit case

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Message-ID: <50912A72.6050307@redhat.com>
Date:	Wed, 31 Oct 2012 15:41:06 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, Rik van Riel <riel@...hat.com>,
	Srikar <srikar@...ux.vnet.ibm.com>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	KVM <kvm@...r.kernel.org>, Jiannan Ouyang <ouyang@...pitt.edu>,
	Chegu Vinod <chegu_vinod@...com>,
	"Andrew M. Theurer" <habanero@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srivatsa Vaddagiri <srivatsa.vaddagiri@...il.com>,
	Gleb Natapov <gleb@...hat.com>,
	Andrew Jones <drjones@...hat.com>
Subject: Re: [PATCH V2 RFC 2/3] kvm: Handle yield_to failure return code for
 potential undercommit case

On 10/31/2012 03:15 PM, Raghavendra K T wrote:
> On 10/31/2012 06:11 PM, Raghavendra K T wrote:
>> On 10/31/2012 06:08 PM, Avi Kivity wrote:
>>> On 10/29/2012 04:07 PM, Raghavendra K T wrote:
>>>> From: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
>>>>
>>>> Also we do not update last boosted vcpu in failure cases.
>>>>
>>>>   #endif
>>>> +
>>>>   void kvm_vcpu_on_spin(struct kvm_vcpu *me)
>>>>   {
>>>>       struct kvm *kvm = me->kvm;
>>>> @@ -1727,11 +1727,12 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
>>>>                   continue;
>>>>               if (!kvm_vcpu_eligible_for_directed_yield(vcpu))
>>>>                   continue;
>>>> -            if (kvm_vcpu_yield_to(vcpu)) {
>>>> +
>>>> +            yielded = kvm_vcpu_yield_to(vcpu);
>>>> +            if (yielded > 0)
>>>>                   kvm->last_boosted_vcpu = i;
>>>> -                yielded = 1;
>>>> +            if (yielded)
>>>>                   break;
>>>> -            }
>>>>           }
>>>
>>> If yielded == -ESRCH, should we not try to yield to another vcpu?
>>>
>>
>>   Yes. plan is to abort the iteration. since it means we are mostly
>> undercommitted.
> 
> Sorry if it was ambiguous. I wanted to say we do not want to continue
> yield to another vcpu..
> 


Why not?  We found that this particular vcpu is running and therefore
likely not a lock holder.  That says nothing about other vcpus.  The
next in line might be runnable-but-not-running on another runqueue.


-- 
error compiling committee.c: too many arguments to function
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