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

[Paolo Bonzini <pbonzini@redhat.com>]

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