Re: [PATCH v4 0/5] remove runnable_load_avg and improve group_classify

[Parth Shah]

Hi,

On 2/21/20 6:57 PM, Vincent Guittot wrote:
> This new version stays quite close to the previous one and should 
> replace without problems the previous one that part of Mel's patchset:
> https://lkml.org/lkml/2020/2/14/156
> 
> NUMA load balancing is the last remaining piece of code that uses the 
> runnable_load_avg of PELT to balance tasks between nodes. The normal
> load_balance has replaced it by a better description of the current state
> of the group of cpus.  The same policy can be applied to the numa
> balancing.
> 
> Once unused, runnable_load_avg can be replaced by a simpler runnable_avg
> signal that tracks the waiting time of tasks on rq. Currently, the state
> of a group of CPUs is defined thanks to the number of running task and the
> level of utilization of rq. But the utilization can be temporarly low
> after the migration of a task whereas the rq is still overloaded with
> tasks. In such case where tasks were competing for the rq, the
> runnable_avg will stay high after the migration.
> 
> Some hackbench results:
> 
> - small arm64 dual quad cores system
> hackbench -l (2560/#grp) -g #grp
> 
> grp    tip/sched/core         +patchset              improvement
> 1       1,327(+/-10,06 %)     1,247(+/-5,45 %)       5,97 %
> 4       1,250(+/- 2,55 %)     1,207(+/-2,12 %)       3,42 %
> 8       1,189(+/- 1,47 %)     1,179(+/-1,93 %)       0,90 %
> 16      1,221(+/- 3,25 %)     1,219(+/-2,44 %)       0,16 %						
> 
> - large arm64 2 nodes / 224 cores system
> hackbench -l (256000/#grp) -g #grp
> 
> grp    tip/sched/core         +patchset              improvement
> 1      14,197(+/- 2,73 %)     13,917(+/- 2,19 %)     1,98 %
> 4       6,817(+/- 1,27 %)      6,523(+/-11,96 %)     4,31 %
> 16      2,930(+/- 1,07 %)      2,911(+/- 1,08 %)     0,66 %
> 32      2,735(+/- 1,71 %)      2,725(+/- 1,53 %)     0,37 %
> 64      2,702(+/- 0,32 %)      2,717(+/- 1,07 %)    -0,53 %
> 128     3,533(+/-14,66 %)     3,123(+/-12,47 %)     11,59 %
> 256     3,918(+/-19,93 %)     3,390(+/- 5,93 %)     13,47 %

[...]

I performed similar experiment on IBM POWER9 system with 2 nodes 44 cores
system (22 per node)

- hackbench -l (256000/#grp) -g #grp
+-----+----------------+-------+
| grp | tip/sched/core |  v4   |
+-----+----------------+-------+
|   1 |          76.97 | 76.31 |
|   4 |          56.56 | 56.86 |
|   8 |          54.23 | 54.25 |
|  16 |          53.94 | 53.24 |
|  32 |          54.10 | 54.01 |
|  64 |          54.38 | 54.35 |
| 128 |          55.11 | 55.08 |
| 256 |          55.97 | 56.04 |
| 512 |          54.81 |  55.5 |
+-----+----------------+-------+
- deviation in the result is very marginal ( < 1%)

The results shows no changes with respect to the hackbench. I will do
further benchmarking to see if any observable changes occurs.


- Parth