On Monday 21 December 2015, Will Deacon wrote: > On Sat, Dec 19, 2015 at 04:11:18PM -0800, Andrew Pinski wrote: > > Adding a check for the cache line size is not much overhead. > > Special case 128 byte cache line size. > > This improves copy_page by 85% on ThunderX compared to the > > original implementation. > > So this patch seems to: > > - Align the loop > - Increase the prefetch size > - Unroll the loop once > > Do you know where your 85% boost comes from between these? I'd really > like to avoid having multiple versions of copy_page, if possible, but > maybe we could end up with something that works well enough regardless > of cacheline size. Understanding what your bottleneck is would help to > lead us in the right direction. > > Also, how are you measuring the improvement? If you can share your > test somewhere, I can see how it affects the other systems I have access > to.
A related question would be how other CPU cores are affected by the change. The test for the cache line size is going to take a few cycles, possibly a lot on certain implementations, e.g. if we ever get one where 'mrs' is microcoded or trapped by a hypervisor. Are there any possible downsides to using the ThunderX version on other microarchitectures too and skip the check? Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/