Re: [PATCH] KVM: Pre-allocate 1 cpumask variable per cpu for both pv tlb and pv ipis

[Wanpeng Li]

On Tue, 4 Feb 2020 at 22:36, Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> wrote:
>
> Wanpeng Li <kernellwp@xxxxxxxxx> writes:
>
> >>
> >> Honestly, I'd simplify the check in kvm_alloc_cpumask() as
> >>
> >> if (!kvm_para_available())
> >>         return;
> >>
> >> and allocated masks for all other cases.
> >
> > This will waste the memory if pv tlb and pv ipis are not exposed which
> > are the only users currently.
> >
>
> My assumption is that the number of cases where we a) expose KVM b)
> don't expose IPIs and PV-TLB and c) care about 1 cpumask per cpu is
> relatively low. Ok, let's at least have a function for
>
>         if (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) &&
>             !kvm_para_has_hint(KVM_HINTS_REALTIME) &&
>             kvm_para_has_feature(KVM_FEATURE_STEAL_TIME))
>
> as we now check it twice: in kvm_alloc_cpumask() and kvm_guest_init(),
> something like pv_tlb_flush_supported(). We can also do
> pv_ipi_supported() and probably others for consistency.

Will do.

    Wanpeng