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

[Jirka Hladky]

> 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 but I
will try to produce patch files for kernel/sched directory only with

git diff v4.4-rc4..fe19159 -- sched

and let you the outcome.



On Sat, Dec 12, 2015 at 8:04 AM, Mike Galbraith
<umgwanakikbuti@xxxxxxxxx> wrote:
> (it's always a good idea to CC subsystem maintainers when reporting)
>
> On Fri, 2015-12-11 at 15:17 +0100, Jirka Hladky wrote:
>> Hello,
>>
>> we are doing performance testing of the new kernel scheduler (commit
>> 53528695ff6d8b77011bc818407c13e30914a946). In most cases we see
>> performance improvements compared to 4.3 kernel with the exception of
>> stream benchmark when running on 4 NUMA node server.
>>
>> When we run 4 stream benchmark processes on 4 NUMA node server and we
>> compare the total performance we see drop about 24% compared to 4.3
>> kernel. This is caused by the fact that 2 stream benchmarks are
>> running on the same NUMA node while 1 NUMA node does not run any
>> stream benchmark. With kernel 4.3, load is distributed evenly among
>> all 4 NUMA nodes. When two stream benchmarks are running on the same
>> NUMA node then the runtime is almost twice as long compared to one
>> stream bench running on one NUMA node. See log files [1] bellow.
>>
>> Please see the graph comparing stream benchmark results between
>> kernel
>> 4.3 and 4.4rc4 (for legend see [2] bellow).
>> https://jhladky.fedorapeople.org/sched_stream_kernel_4.3vs4.4rc4/Stre
>> am_benchmark_on_4_NUMA_node_server_4.3vs4.4rc4_kernel.png
>>
>> Could you please help us to identify the root cause of this
>> regression? We don't have the skills to fix the problem ourselves but
>> we will be more than happy to test any proposed patch for this issue.
>
> A bisection doesn't require any special skills, but may give busy
> maintainers a single change to eyeball vs the entire lot.
>
>         -Mike
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