linux-kernel - Re: [PATCH] KVM: Optimize kvm_arch_vcpu_ioctl

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Date:   Mon, 13 Apr 2020 17:07:28 +0800
From:   Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     pbonzini@...hat.com, sean.j.christopherson@...el.com,
        vkuznets@...hat.com, wanpengli@...cent.com, jmattson@...gle.com,
        joro@...tes.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com, james.morse@....com,
        julien.thierry.kdev@...il.com, suzuki.poulose@....com,
        kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: Optimize kvm_arch_vcpu_ioctl_run function



On 2020/4/13 16:56, Marc Zyngier wrote:
> Tianjia,
> 
> On 2020-04-13 04:45, Tianjia Zhang wrote:
>> kvm_arch_vcpu_ioctl_run() is only called in the file kvm_main.c,
>> where vcpu->run is the kvm_run parameter, so it has been replaced.
>>
>> Signed-off-by: Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
>> ---
>>  arch/x86/kvm/x86.c | 8 ++++----
>>  virt/kvm/arm/arm.c | 2 +-
>>  2 files changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 3bf2ecafd027..70e3f4abbd4d 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -8726,18 +8726,18 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu
>> *vcpu, struct kvm_run *kvm_run)
>>          r = -EAGAIN;
>>          if (signal_pending(current)) {
>>              r = -EINTR;
>> -            vcpu->run->exit_reason = KVM_EXIT_INTR;
>> +            kvm_run->exit_reason = KVM_EXIT_INTR;
>>              ++vcpu->stat.signal_exits;
>>          }
>>          goto out;
>>      }
>>
>> -    if (vcpu->run->kvm_valid_regs & ~KVM_SYNC_X86_VALID_FIELDS) {
>> +    if (kvm_run->kvm_valid_regs & ~KVM_SYNC_X86_VALID_FIELDS) {
>>          r = -EINVAL;
>>          goto out;
>>      }
>>
>> -    if (vcpu->run->kvm_dirty_regs) {
>> +    if (kvm_run->kvm_dirty_regs) {
>>          r = sync_regs(vcpu);
>>          if (r != 0)
>>              goto out;
>> @@ -8767,7 +8767,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu
>> *vcpu, struct kvm_run *kvm_run)
>>
>>  out:
>>      kvm_put_guest_fpu(vcpu);
>> -    if (vcpu->run->kvm_valid_regs)
>> +    if (kvm_run->kvm_valid_regs)
>>          store_regs(vcpu);
>>      post_kvm_run_save(vcpu);
>>      kvm_sigset_deactivate(vcpu);
>> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
>> index 48d0ec44ad77..ab9d7966a4c8 100644
>> --- a/virt/kvm/arm/arm.c
>> +++ b/virt/kvm/arm/arm.c
>> @@ -659,7 +659,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu,
>> struct kvm_run *run)
>>          return ret;
>>
>>      if (run->exit_reason == KVM_EXIT_MMIO) {
>> -        ret = kvm_handle_mmio_return(vcpu, vcpu->run);
>> +        ret = kvm_handle_mmio_return(vcpu, run);
>>          if (ret)
>>              return ret;
>>      }
> 
> Do you have any number supporting the idea that you are optimizing anything
> here? Performance, code size, register pressure or any other relevant 
> metric?
> 
> Thanks,
> 
>          M.

This is only a simplified implementation of the function, the impact on 
performance and register pressure can be ignored.

Thanks,
Tianjia