On Fri, 2013-11-08 at 15:14 -0500, Neil Horman wrote: > On Fri, Nov 08, 2013 at 11:33:13AM -0800, Joe Perches wrote: > > 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? > > > I don't have any hard data no, sorry.
I think you should before you implement this. You might find extremely short lengths. > I'll cap the prefetch at 1500B for now, since it > doesn't seem to hurt or help beyond that The table data has a max prefetch of 8 * boot_cpu_data.x86_cache_alignment so I believe it's always less than 1500 but perhaps 4 might be slightly better still. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
