Messages in this thread |  | | Date | Thu, 28 Oct 2021 19:25:18 -0400 | From | Joel Fernandes <> | Subject | Re: [PATCH v3 0/5] Improve newidle lb cost tracking and early abort |
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Hi, Vincent, Peter,
On Tue, Oct 19, 2021 at 02:35:32PM +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.
It appears this series is not yet in upstream Linus's tree. What's the latest on it?
I see a lot of times on ARM64 devices that load balance is skipped due to the high the sysctl_sched_migration_cost. I saw another thread as well where someone complained the performance varies and the default might be too high: https://lkml.org/lkml/2021/9/14/150
Any other thoughts? Happy to help on any progress on this series as well. Thanks,
- Joel
> > 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 > > Change since v2: > - Update and decay of sd->last_decay_max_lb_cost are gathered in > update_newidle_cost(). The behavior remains almost the same except that > the decay can happen during newidle_balance now. > > Tests results haven't shown any differences > > I haven't modified rq->max_idle_balance_cost. It acts as the max value > for avg_idle and prevents the latter to reach high value during long > idle phase. Moving on an IIR filter instead, could delay the convergence > of avg_idle to a reasonnable value that reflect current situation. > > - Added a minor cleanup of newidle_balance > > Change since v1: > - account the time spent in update_blocked_averages() in the 1st domain > > - reduce number of call of sched_clock_cpu() > > - change the way max_newidle_lb_cost is decayed. Peter suggested to use a > IIR but keeping a track of the current max value gave the best result > > - removed the condition (this_rq->avg_idle < sysctl_sched_migration_cost) > as suggested by Peter > > Vincent Guittot (5): > sched/fair: Account update_blocked_averages in newidle_balance cost > sched/fair: Skip update_blocked_averages if we are defering load > balance > sched/fair: Wait before decaying max_newidle_lb_cost > sched/fair: Remove sysctl_sched_migration_cost condition > sched/fair: cleanup newidle_balance > > include/linux/sched/topology.h | 2 +- > kernel/sched/fair.c | 65 ++++++++++++++++++++++------------ > kernel/sched/topology.c | 2 +- > 3 files changed, 45 insertions(+), 24 deletions(-) > > -- > 2.17.1 >
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