linux-kernel - Re: [PATCH RFC 1/2] kvm: Record the preemption status of vcpus using preempt notifiers

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Message-ID: <51385BA5.7020706@linux.vnet.ibm.com>
Date:	Thu, 07 Mar 2013 14:49:33 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Chegu Vinod <chegu_vinod@...com>, Gleb Natapov <gleb@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Avi Kivity <avi.kivity@...il.com>,
	Ingo Molnar <mingo@...hat.com>, Rik van Riel <riel@...hat.com>,
	Srikar <srikar@...ux.vnet.ibm.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	KVM <kvm@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Jiannan Ouyang <ouyang@...pitt.edu>,
	"Andrew M. Theurer" <habanero@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srivatsa Vaddagiri <srivatsa.vaddagiri@...il.com>,
	Andrew Jones <drjones@...hat.com>
Subject: Re: [PATCH RFC 1/2] kvm: Record the preemption status of vcpus using
 preempt notifiers

On 03/05/2013 08:49 PM, Chegu Vinod wrote:
> On 3/4/2013 10:02 AM, Raghavendra K T wrote:
>> From: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
>>
>> Note that we mark as preempted only when vcpu's task state was
>> Running during preemption.
>>
>> Thanks Jiannan, Avi for preemption notifier ideas. Thanks Gleb, PeterZ
>> for their precious suggestions. Thanks Srikar for an idea on avoiding
>> rcu lock while checking task state that improved overcommit numbers.
>>
>> Signed-off-by: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
>> ---
>>   include/linux/kvm_host.h |    1 +
>>   virt/kvm/kvm_main.c      |    5 +++++
>>   2 files changed, 6 insertions(+)
>>
>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
>> index cad77fe..0b31e1c 100644
>> --- a/include/linux/kvm_host.h
>> +++ b/include/linux/kvm_host.h
>> @@ -252,6 +252,7 @@ struct kvm_vcpu {
>>           bool dy_eligible;
>>       } spin_loop;
>>   #endif
>> +    bool preempted;
>>       struct kvm_vcpu_arch arch;
>>   };
>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>> index adc68fe..83a804c 100644
>> --- a/virt/kvm/kvm_main.c
>> +++ b/virt/kvm/kvm_main.c
>> @@ -244,6 +244,7 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct
>> kvm *kvm, unsigned id)
>>       kvm_vcpu_set_in_spin_loop(vcpu, false);
>>       kvm_vcpu_set_dy_eligible(vcpu, false);
>> +    vcpu->preempted = false;
>>       r = kvm_arch_vcpu_init(vcpu);
>>       if (r < 0)
>> @@ -2902,6 +2903,8 @@ struct kvm_vcpu *preempt_notifier_to_vcpu(struct
>> preempt_notifier *pn)
>>   static void kvm_sched_in(struct preempt_notifier *pn, int cpu)
>>   {
>>       struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn);
>> +    if (vcpu->preempted)
>> +        vcpu->preempted = false;
>>       kvm_arch_vcpu_load(vcpu, cpu);
>>   }
>> @@ -2911,6 +2914,8 @@ static void kvm_sched_out(struct
>> preempt_notifier *pn,
>>   {
>>       struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn);
>> +    if (current->state == TASK_RUNNING)
>> +        vcpu->preempted = true;
>>       kvm_arch_vcpu_put(vcpu);
>>   }
>>
>> .
>>
> Reviewed-by: Chegu Vinod <chegu_vinod@...com>

Thank you Vinod.

Gleb, Marcelo,
  any comment, concern on the patches?


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