Re: [Xen-devel] TLB flushing in blktap kernel driver?

["Andrew Warfield" <andrew.warfield@xxxxxxxxxxxx>]

Agreed -- not sure why that's there, possibly from before the days of
grant tables.  I agree that it can go though.  good catch.

a.

On 9/27/06, Stephen C. Tweedie <sct@xxxxxxxxxx> wrote:
> Hi,
>
> On Wed, 2006-09-27 at 14:30 +0100, Keir Fraser wrote:
> > > However, I can't understand right now why we need the tlb flush here.
> > > If we're doing any grant table operations between dom0 and domU, then
> > > the HV should be doing the tlb flushes for us, shouldn't it?  And mere
> > > SMP synchronisation on a ring buffer requires a physical memory barrier,
> > > not a TLB synchronisation (and RING_PUSH_REQUESTS already does a wmb.)
> >
> > Grant unmapping certainly guarantees to flush TLB entries.
>
> Right.  I can't see why a simple ring buffer poll would *ever* need to
> flush tlbs.  I may be missing something, which is why I asked, but it
> looks like this was perhaps just intended to be a memory barrier, in
> which case the flush call is entirely superfluous (and a significant
> performance hit to boot.)
>
> --Stephen
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