On Mon, Jan 04, 2021 at 03:11:40PM +0100, Michal Hocko wrote: > On Mon 04-01-21 21:34:45, Feng Tang wrote: > > Hi Michal, > > > > On Mon, Jan 04, 2021 at 02:03:57PM +0100, Michal Hocko wrote: > > > On Tue 29-12-20 22:35:13, Feng Tang wrote: > > > > When checking a memory cgroup related performance regression [1], > > > > from the perf c2c profiling data, we found high false sharing for > > > > accessing 'usage' and 'parent'. > > > > > > > > On 64 bit system, the 'usage' and 'parent' are close to each other, > > > > and easy to be in one cacheline (for cacheline size == 64+ B). 'usage' > > > > is usally written, while 'parent' is usually read as the cgroup's > > > > hierarchical counting nature. > > > > > > > > So move the 'parent' to the end of the structure to make sure they > > > > are in different cache lines. > > > > > > Yes, parent is write-once field so having it away from other heavy RW > > > fields makes sense to me. > > > > > > > Following are some performance data with the patch, against > > > > v5.11-rc1, on several generations of Xeon platforms. Most of the > > > > results are improvements, with only one malloc case on one platform > > > > shows a -4.0% regression. Each category below has several subcases > > > > run on different platform, and only the worst and best scores are > > > > listed: > > > > > > > > fio: +1.8% ~ +8.3% > > > > will-it-scale/malloc1: -4.0% ~ +8.9% > > > > will-it-scale/page_fault1: no change > > > > will-it-scale/page_fault2: +2.4% ~ +20.2% > > > > > > What is the second number? Std? > > > > For each case like 'page_fault2', I run several subcases on different > > generations of Xeon, and only listed the lowest (first number) and > > highest (second number) scores. > > > > There are 5 runs and the result are: +3.6%, +2.4%, +10.4%, +20.2%, > > +4.7%, and +2.4% and +20.2% are listed. > > This should be really explained in the changelog and ideally mention the > model as well. Seeing a std would be appreciated as well. I guess I haven't made it clear (due to my poor English :)) The five scores are for different parameters on different HW: Cascadelake (100%) 77844 +3.6% 80667 will-it-scale.per_process_ops Cascadelake (50%) 182475 +2.4% 186866 will-it-scale.per_process_ops Haswell (100%) 84870 +10.4% 93671 will-it-scale.per_process_ops Haswell (50%) 197684 +20.2% 237585 will-it-scale.per_process_ops Newer Xeon (50%) 268569 +4.7% 281320 will-it-scale.per_process_ops +2.4% is the lowest improvement, while +20.2% is the highest. 100% means the number of forked test processes eqauls to CPU number, while 50% is the half. Each line has been runed several times, whose score are consistent without big deviations. Thanks, Feng
