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SubjectRe: [PATCH] x86: Run checksumming in parallel accross multiple alu's
On Fri, Nov 01, 2013 at 01:26:52PM -0700, Joe Perches wrote:
> On Fri, 2013-11-01 at 15:58 -0400, Neil Horman wrote:
> > On Fri, Nov 01, 2013 at 12:45:29PM -0700, Joe Perches wrote:
> > > On Fri, 2013-11-01 at 13:37 -0400, Neil Horman wrote:
> > >
> > > > I think it would be better if we just did the prefetch here
> > > > and re-addressed this area when AVX (or addcx/addox) instructions were available
> > > > for testing on hardware.
> > >
> > > Could there be a difference if only a single software
> > > prefetch was done at the beginning of transfer before
> > > the while loop and hardware prefetches did the rest?
> > >
> > I wouldn't think so. If hardware was going to do any prefetching based on
> > memory access patterns it will do so regardless of the leading prefetch, and
> > that first prefetch isn't helpful because we still wind up stalling on the adds
> > while its completing
>
> I imagine one benefit to be helping prevent
> prefetching beyond the actual data required.
>
> Maybe some hardware optimizes prefetch stride
> better than 5*64.
>
> I wonder also if using
>
> if (count > some_length)
> prefetch
> while (...)
>
> helps small lengths more than the test/jump cost.
>
We've already done this and it is in fact the best performing. I'll be posting
that patch along with ingos request to add do_csum to the perf bench code when I
have that done
Best
Neil

>


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