Re: [RFC PATCH 6/7] arm64: KVM: Handle trappable TLB instructions

Will Deacon
2016-09-01T14:55:23Z

On Fri, Aug 26, 2016 at 10:37:08AM +0100, Punit Agrawal wrote:
> > Will Deacon <will.deacon@arm.com> writes:
> >> The easiest thing to do is just TLBI VMALLE1IS for all trapped operations,
> >> but you might want to see how that performs.
> >
> > That sounds reasonable for correctness. But I suspect we'll have to do
> > more to claw back some performance. Let me run a few tests and come back
> > on this.
>
> Assuming I've correctly switched in TCR and replacing the various TLB
> operations in this patch with TLBI VMALLE1IS, there is a drop in kernel
> build times of ~5% (384s vs 363s).

What do you mean by "switched in TCR"? Why is that necessary if you just
nuke the whole thing? Is the ~5% relative to no trapping at all, or
trapping, but being selective about the operation?

Will