On Sat 21-01-23 20:54:15, Hyeonggon Yoo wrote: > On Sat, Jan 21, 2023 at 12:29:44PM +0100, Vlastimil Babka wrote: > > On 1/21/23 04:39, Hyeonggon Yoo wrote: > > > In workloads where this_cpu operations are frequently performed, > > > enabling DEBUG_PREEMPT may result in significant increase in > > > runtime overhead due to frequent invocation of > > > __this_cpu_preempt_check() function. > > > > > > This can be demonstrated through benchmarks such as hackbench where this > > > configuration results in a 10% reduction in performance, primarily due to > > > the added overhead within memcg charging path. > > > > > > Therefore, do not to enable DEBUG_PREEMPT by default and make users aware > > > of its potential impact on performance in some workloads. > > > > > > hackbench-process-sockets > > > debug_preempt no_debug_preempt > > > Amean 1 0.4743 ( 0.00%) 0.4295 * 9.45%* > > > Amean 4 1.4191 ( 0.00%) 1.2650 * 10.86%* > > > Amean 7 2.2677 ( 0.00%) 2.0094 * 11.39%* > > > Amean 12 3.6821 ( 0.00%) 3.2115 * 12.78%* > > > Amean 21 6.6752 ( 0.00%) 5.7956 * 13.18%* > > > Amean 30 9.6646 ( 0.00%) 8.5197 * 11.85%* > > > Amean 48 15.3363 ( 0.00%) 13.5559 * 11.61%* > > > Amean 79 24.8603 ( 0.00%) 22.0597 * 11.27%* > > > Amean 96 30.1240 ( 0.00%) 26.8073 * 11.01%* Do you happen to have any perf data collected during those runs? I would be interested in the memcg side of things. Maybe we can do something better there. -- Michal Hocko SUSE Labs
