Re: [PATCH v4 RESEND 3/5] KVM: x86: hyperv: use get_vcpu_by_vpidx() in kvm_hv_flush_tlb()

[Vitaly Kuznetsov]

Paolo Bonzini <pbonzini@xxxxxxxxxx> writes:

> On 22/08/2018 12:18, Vitaly Kuznetsov wrote:
>> VP_INDEX almost always matches VCPU id and get_vcpu_by_vpidx() is fast,
>> use it instead of traversing full vCPU list every time.
>
> ... but if it doesn't, the algorithm is now quadratic, isn't i?

Yes,

I even had an implementation with a logarythmic search back in v2 but
we had a discussion with Roman and he convinced me this is an overkill
and not currently required. It seems that with Qemu this is true indeed,
vp_index always matches vcpu is but in case some other userspace decides
to break this unwritten rule users may experience significant slowdown.

-- 
  Vitaly