Messages in this thread |  | | Subject | Re: [PATCH v3 0/5] Improve newidle lb cost tracking and early abort | From | Tim Chen <> | Date | Tue, 26 Oct 2021 10:25:05 -0700 |
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On Tue, 2021-10-19 at 14:35 +0200, Vincent Guittot wrote: > This patchset updates newidle lb cost tracking and early abort: > > The time spent running update_blocked_averages is now accounted in > the 1st > sched_domain level. This time can be significant and move the cost of > newidle lb above the avg_idle time. > > The decay of max_newidle_lb_cost is modified to start only when the > field > has not been updated for a while. Recent update will not be decayed > immediatlybut only after a while. > > The condition of an avg_idle lower than sysctl_sched_migration_cost > has > been removed as the 500us value is quite large and prevent > opportunity to > pull task on the newly idle CPU for at least 1st domain levels. > > Monitoring sd->max_newidle_lb_cost on cpu0 of a Arm64 system > THX2 (2 nodes * 28 cores * 4 cpus) during the benchmarks gives the > following results: > min avg max > SMT: 1us 33us 273us - this one includes the update of blocked > load > MC: 7us 49us 398us > NUMA: 10us 45us 158us > > > Some results for hackbench -l $LOOPS -g $group : > group tip/sched/core + this patchset > 1 15.189(+/- 2%) 14.987(+/- 2%) +1% > 4 4.336(+/- 3%) 4.322(+/- 5%) +0% > 16 3.654(+/- 1%) 2.922(+/- 3%) +20% > 32 3.209(+/- 1%) 2.919(+/- 3%) +9% > 64 2.965(+/- 1%) 2.826(+/- 1%) +4% > 128 2.954(+/- 1%) 2.993(+/- 8%) -1% > 256 2.951(+/- 1%) 2.894(+/- 1%) +2% > > tbench and reaim have not shown any difference >
Vincent,
Our benchmark team tested the patches for our OLTP benchmark on a 2 socket Cascade Lake with 28 cores/socket. It is a smaller configuration than the 2 socket Ice Lake we hae tested previously that has 40 cores/socket so the overhead on update_blocked_averages is smaller (~4%).
Here's a summary of the results: Relative Performance (higher better) 5.15 rc4 vanilla (cgroup disabled) 100% 5.15 rc4 vanilla (cgroup enabled) 96% patch v2 96% patch v3 96%
We didn't see much change in performance from the patch set.
Looking at the profile on update_blocked_averages a bit more, the majority of the call to update_blocked_averages happens in run_rebalance_domain. And we are not including that cost of update_blocked_averages for run_rebalance_domains in our current patch set. I think the patch set should account for that too.
0.60% 0.00% 3 [kernel.vmlinux] [k] run_rebalance_domains - - | --0.59%--run_rebalance_domains | --0.57%--update_blocked_averages
Thanks.
Tim
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