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: <50911C7D.5080307@linux.vnet.ibm.com>
Date:	Wed, 31 Oct 2012 18:11:33 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.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 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.


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