linux-kernel - Scheduler patches: 6x performance increase when system is under heavy load

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Date:   Sun, 11 Dec 2016 16:41:51 -0500
From:   Alexandre-Xavier Labonté-Lamoureux 
        <axdoomer@...il.com>
To:     linux-kernel@...r.kernel.org
Subject: Scheduler patches: 6x performance increase when system is under heavy load

Hi,

There's a research paper[1] called "The Linux Scheduler: a Decade of
Wasted Cores". It shows how the Linux Kernel scheduler is broken and
they provided fixes[2] for some of the know issues that it has. The
changes are illustrated in a presentation[3] that was shown during a
talk.

I patched my kernel with these patches using a simple tool[4]. I
compiled the Linux kernel on it and I was flabbergasted to see an
estimated six times performance increase. It was blazing fast and I
couldn't believe it.

Here are my results (using "time make -j32" on my VM that has 4 cores):

Kernel 4.8.14
  real 26m56.151s
  user 79m52.472s
  sys 7m42.964s

Same kernel, but patched:
  real 4m25.238s
  user 13m52.932s
  sys 1m25.820s

I hope you guys will look into this. If these changes were introduced
into the kernel, it would be great and benefit to a lot of people.
There may be some regression. People have said that it improved the
throughput of the kernel, but on some application such as games, there
are some performance spikes due to overscheduling. This already
happens in the vanilla kernel, but it's worsened a bit. Power
management will also be a thing to look into.

I hope the scheduler engineers will fix the kernel. The research paper
has been out for a while and nothing has been done yet. Personally, I
think six times is huge as someone who compiles huge projects often
and the regressions if any are not apparent to me. Other people should
try it too to test if it's good.

Regards,
Alexandre-Xavier Labonté-Lamoureux

[1] https://www.ece.ubc.ca/~sasha/papers/eurosys16-final29.pdf
[2] https://github.com/Freeaqingme/wastedcores/tree/linux-4.5/patches
[3] http://www.i3s.unice.fr/~jplozi/wastedcores/files/extended_talk.pdf
[4] https://github.com/Turbine1991/build_ubuntu_kernel_wastedcores