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Date: Wed, 31 Oct 2012 18:11:33 +0530
From: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Organization: IBM
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To: Avi Kivity <avi@redhat.com>
CC: Peter Zijlstra <peterz@infradead.org>, "H. Peter Anvin" <hpa@zytor.com>,
        Marcelo Tosatti <mtosatti@redhat.com>, Ingo Molnar <mingo@redhat.com>,
        Rik van Riel <riel@redhat.com>, Srikar <srikar@linux.vnet.ibm.com>,
        "Nikunj A. Dadhania" <nikunj@linux.vnet.ibm.com>,
        KVM <kvm@vger.kernel.org>, Jiannan Ouyang <ouyang@cs.pitt.edu>,
        Chegu Vinod <chegu_vinod@hp.com>,
        "Andrew M. Theurer" <habanero@linux.vnet.ibm.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Srivatsa Vaddagiri <srivatsa.vaddagiri@gmail.com>,
        Gleb Natapov <gleb@redhat.com>, Andrew Jones <drjones@redhat.com>
Subject: Re: [PATCH V2 RFC 2/3] kvm: Handle yield_to failure return code for
 potential undercommit case
References: <20121029140621.15448.92083.sendpatchset@codeblue> <20121029140702.15448.56932.sendpatchset@codeblue> <50911BC3.6080305@redhat.com>
In-Reply-To: <50911BC3.6080305@redhat.com>
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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@linux.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.