linux-kernel - Re: [PATCH v8 1/4] KVM: X86: Add vCPU running/preempted state

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Message-ID: <CANRm+CwN=e9x-t+P3tEb7NvWkWACXvqf1UTG35Cwkxj_Y3HboQ@mail.gmail.com>
Date:   Wed, 13 Dec 2017 19:38:00 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>, Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH v8 1/4] KVM: X86: Add vCPU running/preempted state

2017-12-13 18:20 GMT+08:00 David Hildenbrand <david@...hat.com>:
> On 13.12.2017 02:33, Wanpeng Li wrote:
>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>
>> This patch reuses the preempted field in kvm_steal_time, and will export
>> the vcpu running/pre-empted information to the guest from host. This will
>> enable guest to intelligently send ipi to running vcpus and set flag for
>> pre-empted vcpus. This will prevent waiting for vcpus that are not running.
>>
>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
>> ---
>>  arch/x86/include/uapi/asm/kvm_para.h | 3 +++
>>  arch/x86/kernel/kvm.c                | 2 +-
>>  arch/x86/kvm/x86.c                   | 4 ++--
>>  3 files changed, 6 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
>> index 09cc064..763b692 100644
>> --- a/arch/x86/include/uapi/asm/kvm_para.h
>> +++ b/arch/x86/include/uapi/asm/kvm_para.h
>> @@ -51,6 +51,9 @@ struct kvm_steal_time {
>>       __u32 pad[11];
>>  };
>>
>> +#define KVM_VCPU_NOT_PREEMPTED      (0 << 0)
>> +#define KVM_VCPU_PREEMPTED          (1 << 0)
>
> Is it really helpful to have two flags?
>
> Just use KVM_VCPU_PREEMPTED  and clear that one in record_steal_time()

I think it is fine since there is a third flag introduced in patch
2/4, it is more clear currently.

Regards,
Wanpeng Li