Messages in this thread | | | Date | Fri, 8 Nov 2019 18:37:30 +0000 | From | Mel Gorman <> | Subject | Re: [PATCH v4 04/11] sched/fair: rework load_balance |
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On Fri, Nov 08, 2019 at 05:35:01PM +0100, Vincent Guittot wrote: > > Fair enough, netperf hits the corner case where it does not work but > > that is also true without your series. > > I run mmtest/netperf test on my setup. It's a mix of small positive or > negative differences (see below) > > <SNIP> > > netperf-tcp > 5.3-rc2 5.3-rc2 > tip +rwk+fix > Hmean 64 871.30 ( 0.00%) 860.90 * -1.19%* > Hmean 128 1689.39 ( 0.00%) 1679.31 * -0.60%* > Hmean 256 3199.59 ( 0.00%) 3241.98 * 1.32%* > Hmean 1024 9390.47 ( 0.00%) 9268.47 * -1.30%* > Hmean 2048 13373.95 ( 0.00%) 13395.61 * 0.16%* > Hmean 3312 16701.30 ( 0.00%) 17165.96 * 2.78%* > Hmean 4096 15831.03 ( 0.00%) 15544.66 * -1.81%* > Hmean 8192 19720.01 ( 0.00%) 20188.60 * 2.38%* > Hmean 16384 23925.90 ( 0.00%) 23914.50 * -0.05%* > Stddev 64 7.38 ( 0.00%) 4.23 ( 42.67%) > Stddev 128 11.62 ( 0.00%) 10.13 ( 12.85%) > Stddev 256 34.33 ( 0.00%) 7.94 ( 76.88%) > Stddev 1024 35.61 ( 0.00%) 116.34 (-226.66%) > Stddev 2048 285.30 ( 0.00%) 80.50 ( 71.78%) > Stddev 3312 304.74 ( 0.00%) 449.08 ( -47.36%) > Stddev 4096 668.11 ( 0.00%) 569.30 ( 14.79%) > Stddev 8192 733.23 ( 0.00%) 944.38 ( -28.80%) > Stddev 16384 553.03 ( 0.00%) 299.44 ( 45.86%) > > 5.3-rc2 5.3-rc2 > tip +rwk+fix > Duration User 138.05 140.95 > Duration System 1210.60 1208.45 > Duration Elapsed 1352.86 1352.90 >
This roughly matches what I've seen. The interesting part to me for netperf is the next section of the report that reports the locality of numa hints. With netperf on a 2-socket machine, it's generally around 50% as the client/server are pulled apart. Because netperf is not heavily memory bound, it doesn't have much impact on the overall performance but it's good at catching the cross-node migrations.
> > > > > I agree that additional patches are probably needed to improve load > > > balance at NUMA level and I expect that this rework will make it > > > simpler to add. > > > I just wanted to get the output of some real use cases before defining > > > more numa level specific conditions. Some want to spread on there numa > > > nodes but other want to keep everything together. The preferred node > > > and fbq_classify_group was the only sensible metrics to me when he > > > wrote this patchset but changes can be added if they make sense. > > > > > > > That's fair. While it was possible to address the case before your > > series, it was a hatchet job. If the changelog simply notes that some > > special casing may still be required for SD_NUMA but it's outside the > > scope of the series, then I'd be happy. At least there is a good chance > > then if there is follow-up work that it won't be interpreted as an > > attempt to reintroduce hacky heuristics. > > > > Would the additional comment make sense for you about work to be done > for SD_NUMA ? > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 0ad4b21..7e4cb65 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6960,11 +6960,34 @@ enum fbq_type { regular, remote, all }; > * group. see update_sd_pick_busiest(). > */ > enum group_type { > + /* > + * The group has spare capacity that can be used to process more work. > + */ > group_has_spare = 0, > + /* > + * The group is fully used and the tasks don't compete for more CPU > + * cycles. Nevetheless, some tasks might wait before running. > + */ > group_fully_busy, > + /* > + * One task doesn't fit with CPU's capacity and must be migrated on a > + * more powerful CPU. > + */ > group_misfit_task, > + /* > + * One local CPU with higher capacity is available and task should be > + * migrated on it instead on current CPU. > + */ > group_asym_packing, > + /* > + * The tasks affinity prevents the scheduler to balance the load across > + * the system. > + */ > group_imbalanced, > + /* > + * The CPU is overloaded and can't provide expected CPU cycles to all > + * tasks. > + */ > group_overloaded > };
Looks good.
> > @@ -8563,7 +8586,11 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s > > /* > * Try to use spare capacity of local group without overloading it or > - * emptying busiest > + * emptying busiest. > + * XXX Spreading tasks across numa nodes is not always the best policy > + * and special cares should be taken for SD_NUMA domain level before > + * spreading the tasks. For now, load_balance() fully relies on > + * NUMA_BALANCING and fbq_classify_group/rq to overide the decision. > */ > if (local->group_type == group_has_spare) { > if (busiest->group_type > group_fully_busy) {
Perfect. Any patch in that are can then update the comment and it should be semi-obvious to the next reviewer that it's expected.
Thanks Vincent.
-- Mel Gorman SUSE Labs
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