Messages in this thread |  | | Subject | Re: [PATCH] x86: Run checksumming in parallel accross multiple alu's | From | Joe Perches <> | Date | Fri, 01 Nov 2013 13:26:52 -0700 |
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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.
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