Re: sched : performance regression 24% between 4.4rc4 and 4.3 kernel

[Jirka Hladky]

Hi all,

I have the results of bisecting:

first bad commit: [973759c80db96ed4b4c5cb85ac7d48107f801371] Merge tag
'v4.3-rc1' into sched/core, to refresh the branch

Could you please have a look at this commit why it has caused the
performance regression when running 4 stream benchmarks in parallel on
4 NUMA node server?

Please let me know if you need additional data. git bisect log is bellow.

Thanks a lot!
Jirka



$ git bisect log
git bisect start '--' 'kernel/sched'
# good: [6a13feb9c82803e2b815eca72fa7a9f5561d7861] Linux 4.3
git bisect good 6a13feb9c82803e2b815eca72fa7a9f5561d7861
# bad: [527e9316f8ec44bd53d90fb9f611fa7ffff52bb9] Linux 4.4-rc4
git bisect bad 527e9316f8ec44bd53d90fb9f611fa7ffff52bb9
# bad: [b99def8b961448f5b9a550dddeeb718e3975e7a6] sched/core: Rework
TASK_DEAD preemption exception
git bisect bad b99def8b961448f5b9a550dddeeb718e3975e7a6
# skip: [8cd5601c50603caa195ce86cc465cb04079ed488] sched/fair: Convert
arch_scale_cpu_capacity() from weak function to #define
git bisect skip 8cd5601c50603caa195ce86cc465cb04079ed488
# bad: [fe19159225d8516f3f57a5fe8f735c01684f0ddd] Merge branch
'sched/urgent' into sched/core, to pick up fixes before applying new
changes
git bisect bad fe19159225d8516f3f57a5fe8f735c01684f0ddd
# bad: [78a9c54649ea220065aad9902460a1d137c7eafd] sched/numa: Rename
numabalancing_enabled to sched_numa_balancing
git bisect bad 78a9c54649ea220065aad9902460a1d137c7eafd
# bad: [6efdb105d392da3ad5cb4ef951aed373cd049813] sched/fair: Fix
switched_to_fair()'s per entity load tracking
git bisect bad 6efdb105d392da3ad5cb4ef951aed373cd049813
# bad: [50a2a3b246149d041065a67ccb3e98145f780a2f] sched/fair: Have
task_move_group_fair() unconditionally add the entity load to the
runqueue
git bisect bad 50a2a3b246149d041065a67ccb3e98145f780a2f
# bad: [973759c80db96ed4b4c5cb85ac7d48107f801371] Merge tag 'v4.3-rc1'
into sched/core, to refresh the branch
git bisect bad 973759c80db96ed4b4c5cb85ac7d48107f801371
# first bad commit: [973759c80db96ed4b4c5cb85ac7d48107f801371] Merge
tag 'v4.3-rc1' into sched/core, to refresh the branch

On Sat, Dec 12, 2015 at 3:37 PM, Mike Galbraith
<umgwanakikbuti@xxxxxxxxx> wrote:
> On Sat, 2015-12-12 at 15:16 +0100, Jirka Hladky wrote:
>> > A bisection doesn't require any special skills, but may give busy
>> > maintainers a single change to eyeball vs the entire lot.
>>
>> They have been couple of merges which makes git revert difficult...
>
> You could try https://git-scm.com/docs/git-bisect instead.
>
>         -Mike
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