Re: [PATCH v2] KVM: x86: count actual tlb flushes

[Liang Chen <liangchen.linux@gmail.com>]

On 09/18/2014 08:47 AM, Paolo Bonzini wrote:
> Il 18/09/2014 07:05, Xiao Guangrong ha scritto:
>> On 09/18/2014 02:35 AM, Liang Chen wrote:
>>> - we count KVM_REQ_TLB_FLUSH requests, not actual flushes
>>> (KVM can have multiple requests for one flush)
>>> - flushes from kvm_flush_remote_tlbs aren't counted
>>> - it's easy to make a direct request by mistake
>>>
>>> Solve these by postponing the counting to kvm_check_request(),
>> It's good.
>>
>>> and refactor the code to use kvm_make_request again.
>> Why this refactor is needed? It's really a bad idea using
>> raw-bit-set instead of meaningful name.
> set_bit is worse than kvm_make_request, but adding a one-line wrapper
> around kvm_make_request is not particularly useful.
>
> We have the following requests:
>
> - used multiple times:
>         kvm_make_request(KVM_REQ_APF_HALT, vcpu);
>         kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
>         kvm_make_request(KVM_REQ_EVENT, vcpu);
>         kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu);
>         kvm_make_request(KVM_REQ_PMU, pmc->vcpu);
>         kvm_make_request(KVM_REQ_STEAL_UPDATE, vcpu);
>         kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
>         kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
>
> - used once:
>         kvm_make_request(KVM_REQ_DEACTIVATE_FPU, vcpu);
>         kvm_make_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu);
>         kvm_make_request(KVM_REQ_MMU_SYNC, vcpu);
>         kvm_make_request(KVM_REQ_NMI, vcpu);
>         kvm_make_request(KVM_REQ_PENDING_TIMER, vcpu);
>         kvm_make_request(KVM_REQ_PMI, pmc->vcpu);
>         kvm_make_request(KVM_REQ_REPORT_TPR_ACCESS, vcpu);
>
> So I'm pretty much ambivalent about that.  However, I agree with this
> suggestion:
>
>> [ Btw, maybe kvm_mmu_flush_local_tlb is a better name than
>> kvm_mmu_flush_tlb() in the current code. ]
> Or even better, call it kvm_vcpu_flush_tlb since it is all within
> x86.c/vmx.c/svm.c and the MMU is not involved at all.
>
> Paolo

Thanks for the quick feedback! I will incorporate the name change into the
next iteration of the patch.

Thanks!
Liang Chen