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

[Marc Zyngier <maz@kernel.org>]

On Wed, 18 Aug 2021 17:15:36 +0100,
Jing Zhang <jingzhangos@google.com> wrote:
> 
> 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"?

Yes, this is what I meant, as I only quoted the bit that was redundant.

> These two counters would have the same value for arm64, but not for
> others (at least x86).

Sure. It is just that this patch does two things at once, but doesn't
advertise it.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.
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