Re: [PATCH] KVM: stats: Add VM stat for remote tlb flush requests

[Jing Zhang <jingzhangos@google.com>]

Hi Marc,

On Wed, Aug 18, 2021 at 1:11 AM Marc Zyngier <maz@kernel.org> wrote:
>
> On Tue, 17 Aug 2021 01:26:39 +0100,
> Jing Zhang <jingzhangos@google.com> wrote:
> >
> > Add a new stat that counts the number of times a remote TLB flush is
> > requested, regardless of whether it kicks vCPUs out of guest mode. This
> > allows us to look at how often flushes are initiated.
>
> nit: this is a very x86-centric view of things. On arm64, TLB
> invalidation is broadcast in HW, and does not interrupt the guest
> execution.
>
Understood. Thanks.
> >
> > Original-by: David Matlack <dmatlack@google.com>
> > Signed-off-by: Jing Zhang <jingzhangos@google.com>
> > ---
> >  arch/arm64/kvm/mmu.c      | 1 +
> >  include/linux/kvm_host.h  | 3 ++-
> >  include/linux/kvm_types.h | 1 +
> >  virt/kvm/kvm_main.c       | 1 +
> >  4 files changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> > index 0625bf2353c2..f5bb235bbb59 100644
> > --- a/arch/arm64/kvm/mmu.c
> > +++ b/arch/arm64/kvm/mmu.c
> > @@ -80,6 +80,7 @@ static bool memslot_is_logging(struct kvm_memory_slot *memslot)
> >   */
> >  void kvm_flush_remote_tlbs(struct kvm *kvm)
> >  {
> > +     ++kvm->stat.generic.remote_tlb_flush_requests;
> >       kvm_call_hyp(__kvm_tlb_flush_vmid, &kvm->arch.mmu);
> >  }
>
> We already have this queued for 5.15 [1].
I guess you mean the change for "remote_tlb_flush" has been queued,
not "remote_tlb_flush_requests"?
These two counters would have the same value for arm64, but not for
others (at least x86).
>
> Thanks,
>
>         M.
>
> [1] https://lore.kernel.org/r/20210727103251.16561-1-pbonzini@redhat.com
>
> --
> Without deviation from the norm, progress is not possible.

Thanks,
Jing