Messages in this thread | | | Subject | Re: [PATCH v2 2/2] x86: add prefetching to do_csum | From | Joe Perches <> | Date | Fri, 08 Nov 2013 11:33:13 -0800 |
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On Fri, 2013-11-08 at 14:01 -0500, Neil Horman wrote: > 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)); > > > > Just tested this out:
Thanks.
Reformatting the table so it's a bit more readable/comparable for me:
len SetSz Loops cycles/byte limited unlimited 1500B 64MB 1M 1.3442 1.3605 1500B 128MB 1M 1.3410 1.3542 1500B 256MB 1M 1.3536 1.3710 1500B 512MB 1M 1.3463 1.3536 9000B 64MB 1M 0.8522 0.8504 9000B 128MB 1M 0.8528 0.8536 9000B 256MB 1M 0.8532 0.8520 9000B 512MB 1M 0.8527 0.8525 64KB 64MB 1M 0.7686 0.7683 64KB 128MB 1M 0.7695 0.7686 64KB 256MB 1M 0.7699 0.7708 64KB 512MB 1M 0.7799 0.7694
This data appears to show some value in capping for 1500b lengths and noise for shorter and longer lengths.
Any idea what the actual distribution of do_csum lengths is under various loads?
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