Messages in this thread | | | Date | Wed, 6 Nov 2013 15:02:04 -0500 | From | Neil Horman <> | Subject | Re: [PATCH v2 2/2] x86: add prefetching to do_csum |
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On Wed, Nov 06, 2013 at 09:19:23AM -0800, Joe Perches wrote: > On Wed, 2013-11-06 at 10:54 -0500, Neil Horman wrote: > > On Wed, Nov 06, 2013 at 10:34:29AM -0500, Dave Jones wrote: > > > On Wed, Nov 06, 2013 at 10:23:19AM -0500, Neil Horman wrote: > > > > do_csum was identified via perf recently as a hot spot when doing > > > > receive on ip over infiniband workloads. After alot of testing and > > > > ideas, we found the best optimization available to us currently is to > > > > prefetch the entire data buffer prior to doing the checksum > [] > > I'll fix this up and send a v3, but I'll give it a day in case there are more > > comments first. > > Perhaps a reduction in prefetch loop count helps. > > Was capping the amount prefetched and letting the > hardware prefetch also tested? > > prefetch_lines(buff, min(len, cache_line_size() * 8u)); > > Also pedantry/trivial comments: > > __always_inline instead of inline > static __always_inline void prefetch_lines(const void *addr, size_t len) > { > const void *end = addr + len; > ... > > buff doesn't need a void * cast in prefetch_lines > Actually I take back what I said here, we do need the cast, not for a conversion from unsigned char * to void *, but rather to discard the const qualifier without making the compiler complain.
Neil
> Beside the commit message, the comment above prefetch_lines > also needs updating to remove the "Manual Prefetching" line. > > /* > * Do a 64-bit checksum on an arbitrary memory area. > * Returns a 32bit checksum. > * > * This isn't as time critical as it used to be because many NICs > * do hardware checksumming these days. > * > * Things tried and found to not make it faster: > * Manual Prefetching > * Unrolling to an 128 bytes inner loop. > */ > > >
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