On Tue 19-01-21 15:20:14, 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. > > Following are some performance data with the patch, against > v5.11-rc1. [ In the data, A means a platform with 2 sockets 48C/96T, > B is a platform of 4 sockests 72C/144T, and if a %stddev will be > shown bigger than 2%, P100/P50 means number of test tasks equals > to 100%/50% of nr_cpu] > > will-it-scale/malloc1 > --------------------- > v5.11-rc1 v5.11-rc1+patch > > A-P100 15782 ± 2% -0.1% 15765 ± 3% will-it-scale.per_process_ops > A-P50 21511 +8.9% 23432 will-it-scale.per_process_ops > B-P100 9155 +2.2% 9357 will-it-scale.per_process_ops > B-P50 10967 +7.1% 11751 ± 2% will-it-scale.per_process_ops > > will-it-scale/pagefault2 > ------------------------ > v5.11-rc1 v5.11-rc1+patch > > A-P100 79028 +3.0% 81411 will-it-scale.per_process_ops > A-P50 183960 ± 2% +4.4% 192078 ± 2% will-it-scale.per_process_ops > B-P100 85966 +9.9% 94467 ± 3% will-it-scale.per_process_ops > B-P50 198195 +9.8% 217526 will-it-scale.per_process_ops > > fio (4k/1M is block size) > ------------------------- > v5.11-rc1 v5.11-rc1+patch > > A-P50-r-4k 16881 ± 2% +1.2% 17081 ± 2% fio.read_bw_MBps > A-P50-w-4k 3931 +4.5% 4111 ± 2% fio.write_bw_MBps > A-P50-r-1M 15178 -0.2% 15154 fio.read_bw_MBps > A-P50-w-1M 3924 +0.1% 3929 fio.write_bw_MBps Thanks for making results easier to read and understand. > [1].https://lore.kernel.org/lkml/20201102091543.GM31092@shao2-debian/ > Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx> > Reviewed-by: Roman Gushchin <guro@xxxxxx> > Cc: Johannes Weiner <hannes@xxxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Thanks! > --- > Changelogs: > > v2: > * Adjust the format of performance data to be more readable, > as suggested by Michal Hocko > > include/linux/page_counter.h | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h > index 85bd413..6795913 100644 > --- a/include/linux/page_counter.h > +++ b/include/linux/page_counter.h > @@ -12,7 +12,6 @@ struct page_counter { > unsigned long low; > unsigned long high; > unsigned long max; > - struct page_counter *parent; > > /* effective memory.min and memory.min usage tracking */ > unsigned long emin; > @@ -27,6 +26,14 @@ struct page_counter { > /* legacy */ > unsigned long watermark; > unsigned long failcnt; > + > + /* > + * 'parent' is placed here to be far from 'usage' to reduce > + * cache false sharing, as 'usage' is written mostly while > + * parent is frequently read for cgroup's hierarchical > + * counting nature. > + */ > + struct page_counter *parent; > }; > > #if BITS_PER_LONG == 32 > -- > 2.7.4 > -- Michal Hocko SUSE Labs
