Re: [PATCH v2 0/8] sched/fair: rework the CFS load balance
Hi Phil, On Thu, 29 Aug 2019 at 21:23, Phil Auld wrote: > > On Thu, Aug 01, 2019 at 04:40:16PM +0200 Vincent Guittot wrote: > > Several wrong task placement have been raised with the current load > > > > -- > > 2.7.4 > > > > I keep expecting a v3 so I have not dug into all the patches in detail. > However, I've v3 is under preparation > been working with them from Vincent's tree while they were under development > so I thought > I'd add some results. Yes. thanks for your help. > > The workload is a test our perf team came up with to illustrate the issues we > were seeing > with imbalance in the presence of group scheduling. > > On a 4-numa X 20 cpu system (smt on) we run a 76 thread lu.C benchmark from > the NAS Parallel > suite. And at the same time run 2 stress cpu burn processes. The GROUP test > puts the > benchmark and the stress processes each in its own cgroup. The NORMAL case > puts them all > in the first cgroup. The results show first the average number of threads of > each type > running on each of the numa nodes based on sampling taken during the run. > This is followed > by the lu.C benchmark results. There are 3 runs of GROUP and 2 runs of NORMAL > shown. > > Before (linux-5.3-rc1+ @ a1dc0446d649) > > lu.C.x_76_GROUP_1.stress.ps.numa.hist Average0.00 1.00 1.00 > lu.C.x_76_GROUP_2.stress.ps.numa.hist Average0.00 1.00 1.00 > lu.C.x_76_GROUP_3.stress.ps.numa.hist Average0.00 1.00 1.00 > lu.C.x_76_NORMAL_1.stress.ps.numa.hist Average1.15 0.23 0.00 0.62 > lu.C.x_76_NORMAL_2.stress.ps.numa.hist Average1.67 0.00 0.00 0.33 > > lu.C.x_76_GROUP_1.ps.numa.hist Average30.45 6.95 4.52 34.08 > lu.C.x_76_GROUP_2.ps.numa.hist Average32.33 8.94 9.21 25.52 > lu.C.x_76_GROUP_3.ps.numa.hist Average30.45 8.91 12.09 24.55 > lu.C.x_76_NORMAL_1.ps.numa.hist Average18.54 19.23 19.69 18.54 > lu.C.x_76_NORMAL_2.ps.numa.hist Average17.25 19.83 20.00 18.92 > > 76_GROUPMop/s=== > min q1 median q3 max > 2119.92 2418.1 2716.28 3147.82 3579.36 > 76_GROUPtime > min q1 median q3 max > 569.65 660.155 750.66 856.245 961.83 > 76_NORMALMop/s=== > min q1 median q3 max > 30424.5 31486.4 31486.4 31486.4 32548.4 > 76_NORMALtime > min q1 median q3 max > 62.65 64.835 64.835 64.835 67.02 > > > After (linux-5.3-rc1+ @ a1dc0446d649 + this v2 series pulled from > Vincent's git on ~8/15) > > lu.C.x_76_GROUP_1.stress.ps.numa.hist Average0.36 1.00 0.64 > lu.C.x_76_GROUP_2.stress.ps.numa.hist Average1.00 1.00 > lu.C.x_76_GROUP_3.stress.ps.numa.hist Average1.00 1.00 > lu.C.x_76_NORMAL_1.stress.ps.numa.hist Average0.23 0.15 0.31 1.31 > lu.C.x_76_NORMAL_2.stress.ps.numa.hist Average1.00 0.00 0.00 1.00 > > lu.C.x_76_GROUP_1.ps.numa.hist Average18.91 18.36 18.91 19.82 > lu.C.x_76_GROUP_2.ps.numa.hist Average18.36 18.00 19.91 19.73 > lu.C.x_76_GROUP_3.ps.numa.hist Average18.17 18.42 19.25 20.17 > lu.C.x_76_NORMAL_1.ps.numa.hist Average19.08 20.00 18.62 18.31 > lu.C.x_76_NORMAL_2.ps.numa.hist Average18.09 19.91 19.18 18.82 > > 76_GROUPMop/s=== > min q1 median q3 max > 32304.1 33176 34047.9 34166.8 34285.7 > 76_GROUPtime > min q1 median q3 max > 59.47 59.68 59.89 61.505 63.12 > 76_NORMALMop/s=== > min q1 median q3 max > 29825.5 32454 32454 32454 35082.5 > 76_NORMALtime > min q1 median q3 max > 58.12 63.24 63.24 63.24 68.36 > > > I had initially tracked this down to two issues. The first was picking the > wrong > group in find_busiest_group due to using the average load. The second was in > fix_small_imbalance(). The "load" of the lu.C tasks was so low it often failed > to move anything even when it did find a group that was overloaded (nr_running > > width). I have two small patches which fix this but since Vincent was > > embarking > on a re-work which also addressed this I dropped them. > > We've also run a series of performance tests we use to check for regressions > and > did not find any bad results on our workloads and systems. > > So... > > Tested-by: Phil Auld Thanks for testing Vincent > > > Cheers, > Phil > --
Re: [PATCH v2 0/8] sched/fair: rework the CFS load balance
On Thu, Aug 01, 2019 at 04:40:16PM +0200 Vincent Guittot wrote:
> Several wrong task placement have been raised with the current load
> balance algorithm but their fixes are not always straight forward and
> end up with using biased values to force migrations. A cleanup and rework
> of the load balance will help to handle such UCs and enable to fine grain
> the behavior of the scheduler for other cases.
>
> Patch 1 has already been sent separatly and only consolidate asym policy
> in one place and help the review of the changes in load_balance.
>
> Patch 2 renames the sum of h_nr_running in stats.
>
> Patch 3 removes meaningless imbalance computation to make review of
> patch 4 easier.
>
> Patch 4 reworks load_balance algorithm and fixes some wrong task placement
> but try to stay conservative.
>
> Patch 5 add the sum of nr_running to monitor non cfs tasks and take that
> into account when pulling tasks.
>
> Patch 6 replaces runnable_load by load now that the metrics is only used
> when overloaded.
>
> Patch 7 improves the spread of tasks at the 1st scheduling level.
>
> Patch 8 uses utilization instead of load in all steps of misfit task
> path.
>
> Some benchmarks results based on 8 iterations of each tests:
> - small arm64 dual quad cores system
>
>tip/sched/corew/ this patchsetimprovement
> schedpipe 54981 +/-0.36%55459 +/-0.31% (+0.97%)
>
> hackbench
> 1 groups 0.906 +/-2.34%0.906 +/-2.88% (+0.06%)
>
> - large arm64 2 nodes / 224 cores system
>
>tip/sched/corew/ this patchsetimprovement
> schedpipe 125665 +/-0.61% 125455 +/-0.62% (-0.17%)
>
> hackbench -l (256000/#grp) -g #grp
> 1 groups 15.263 +/-3.53% 13.776 +/-3.30% (+9.74%)
> 4 groups 5.852 +/-0.57%5.340 +/-8.03% (+8.75%)
> 16 groups 3.097 +/-1.08%3.246 +/-0.97% (-4.81%)
> 32 groups 2.882 +/-1.04%2.845 +/-1.02% (+1.29%)
> 64 groups 2.809 +/-1.30%2.712 +/-1.17% (+3.45%)
> 128 groups 3.129 +/-9.74%2.813 +/-6.22% (+9.11%)
> 256 groups 3.559 +/-11.07% 3.020 +/-1.75% (+15.15%)
>
> dbench
> 1 groups 330.897 +/-0.27% 330.612 +/-0.77% (-0.09%)
> 4 groups 932.922 +/-0.54% 941.817 +/*1.10% (+0.95%)
> 16 groups 1932.346 +/-1.37% 1962.944 +/-0.62% (+1.58%)
> 32 groups 2251.079 +/-7.93% 2418.531 +/-0.69% (+7.44%)
> 64 groups 2104.114 +/-9.67% 2348.698 +/-11.24% (+11.62%)
> 128 groups 2093.756 +/-7.26% 2278.156 +/-9.74% (+8.81%)
> 256 groups 1216.736 +/-2.46% 1665.774 +/-4.68% (+36.91%)
>
> tip/sched/core sha1:
> a1dc0446d649 ('sched/core: Silence a warning in sched_init()')
>
> Changes since v1:
> - fixed some bugs
> - Used switch case
> - Renamed env->src_grp_type to env->balance_type
> - split patches in smaller ones
> - added comments
>
> Vincent Guittot (8):
> sched/fair: clean up asym packing
> sched/fair: rename sum_nr_running to sum_h_nr_running
> sched/fair: remove meaningless imbalance calculation
> sched/fair: rework load_balance
> sched/fair: use rq->nr_running when balancing load
> sched/fair: use load instead of runnable load
> sched/fair: evenly spread tasks when not overloaded
> sched/fair: use utilization to select misfit task
>
> kernel/sched/fair.c | 769
> ---
> kernel/sched/sched.h | 2 +-
> 2 files changed, 419 insertions(+), 352 deletions(-)
>
> --
> 2.7.4
>
I keep expecting a v3 so I have not dug into all the patches in detail.
However, I've
been working with them from Vincent's tree while they were under development so
I thought
I'd add some results.
The workload is a test our perf team came up with to illustrate the issues we
were seeing
with imbalance in the presence of group scheduling.
On a 4-numa X 20 cpu system (smt on) we run a 76 thread lu.C benchmark from the
NAS Parallel
suite. And at the same time run 2 stress cpu burn processes. The GROUP test
puts the
benchmark and the stress processes each in its own cgroup. The NORMAL case
puts them all
in the first cgroup. The results show first the average number of threads of
each type
running on each of the numa nodes based on sampling taken during the run. This
is followed
by the lu.C benchmark results. There are 3 runs of GROUP and 2 runs of NORMAL
shown.
Before (linux-5.3-rc1+ @ a1dc0446d649)
lu.C.x_76_GROUP_1.stress.ps.numa.hist Average0.00 1.00 1.00
lu.C.x_76_GROUP_2.stress.ps.numa.hist Average0.00 1.00 1.00
lu.C.x_76_GROUP_3.stress.ps.numa.hist Average0.00 1.00 1.00
lu.C.x_76_NORMAL_1.stress.ps.numa.hist Average1.15 0.23 0.00 0.62
lu.C.x_76_NORMAL_2.stress.ps.numa.hist Average1.67 0.00 0.00 0.33
lu.C.x_76_GROUP_1.ps.numa.hist Average30.45 6.95 4.52 34.08
lu.C.x_76_GROUP_2.ps.numa.hist Average32.33 8.94 9.21 25.52
lu.C.x_76_GROUP_3.ps.numa.hist Average
[PATCH v2 0/8] sched/fair: rework the CFS load balance
Several wrong task placement have been raised with the current load
balance algorithm but their fixes are not always straight forward and
end up with using biased values to force migrations. A cleanup and rework
of the load balance will help to handle such UCs and enable to fine grain
the behavior of the scheduler for other cases.
Patch 1 has already been sent separatly and only consolidate asym policy
in one place and help the review of the changes in load_balance.
Patch 2 renames the sum of h_nr_running in stats.
Patch 3 removes meaningless imbalance computation to make review of
patch 4 easier.
Patch 4 reworks load_balance algorithm and fixes some wrong task placement
but try to stay conservative.
Patch 5 add the sum of nr_running to monitor non cfs tasks and take that
into account when pulling tasks.
Patch 6 replaces runnable_load by load now that the metrics is only used
when overloaded.
Patch 7 improves the spread of tasks at the 1st scheduling level.
Patch 8 uses utilization instead of load in all steps of misfit task
path.
Some benchmarks results based on 8 iterations of each tests:
- small arm64 dual quad cores system
tip/sched/corew/ this patchsetimprovement
schedpipe 54981 +/-0.36%55459 +/-0.31% (+0.97%)
hackbench
1 groups 0.906 +/-2.34%0.906 +/-2.88% (+0.06%)
- large arm64 2 nodes / 224 cores system
tip/sched/corew/ this patchsetimprovement
schedpipe 125665 +/-0.61% 125455 +/-0.62% (-0.17%)
hackbench -l (256000/#grp) -g #grp
1 groups 15.263 +/-3.53% 13.776 +/-3.30% (+9.74%)
4 groups 5.852 +/-0.57%5.340 +/-8.03% (+8.75%)
16 groups 3.097 +/-1.08%3.246 +/-0.97% (-4.81%)
32 groups 2.882 +/-1.04%2.845 +/-1.02% (+1.29%)
64 groups 2.809 +/-1.30%2.712 +/-1.17% (+3.45%)
128 groups 3.129 +/-9.74%2.813 +/-6.22% (+9.11%)
256 groups 3.559 +/-11.07% 3.020 +/-1.75% (+15.15%)
dbench
1 groups 330.897 +/-0.27% 330.612 +/-0.77% (-0.09%)
4 groups 932.922 +/-0.54% 941.817 +/*1.10% (+0.95%)
16 groups 1932.346 +/-1.37% 1962.944 +/-0.62% (+1.58%)
32 groups 2251.079 +/-7.93% 2418.531 +/-0.69% (+7.44%)
64 groups 2104.114 +/-9.67% 2348.698 +/-11.24% (+11.62%)
128 groups 2093.756 +/-7.26% 2278.156 +/-9.74% (+8.81%)
256 groups 1216.736 +/-2.46% 1665.774 +/-4.68% (+36.91%)
tip/sched/core sha1:
a1dc0446d649 ('sched/core: Silence a warning in sched_init()')
Changes since v1:
- fixed some bugs
- Used switch case
- Renamed env->src_grp_type to env->balance_type
- split patches in smaller ones
- added comments
Vincent Guittot (8):
sched/fair: clean up asym packing
sched/fair: rename sum_nr_running to sum_h_nr_running
sched/fair: remove meaningless imbalance calculation
sched/fair: rework load_balance
sched/fair: use rq->nr_running when balancing load
sched/fair: use load instead of runnable load
sched/fair: evenly spread tasks when not overloaded
sched/fair: use utilization to select misfit task
kernel/sched/fair.c | 769 ---
kernel/sched/sched.h | 2 +-
2 files changed, 419 insertions(+), 352 deletions(-)
--
2.7.4
