linux-kernel - Re: CFS scheduler unfairly prefers pinned tasks

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Message-Id: <201510112059.t9BKxkNv007161@como.maths.usyd.edu.au>
Date:	Mon, 12 Oct 2015 07:59:46 +1100
From:	paul.szabo@...ney.edu.au
To:	umgwanakikbuti@...il.com
Cc:	linux-kernel@...r.kernel.org, peterz@...radead.org,
	wanpeng.li@...mail.com
Subject: Re: CFS scheduler unfairly prefers pinned tasks

I wrote:

  The Linux CFS scheduler prefers pinned tasks and unfairly
  gives more CPU time to tasks that have set CPU affinity.
  ...
  I believe I have now solved the problem, simply by setting:
    for n in /proc/sys/kernel/sched_domain/cpu*/domain0/min_interval; do echo 0 > $n; done
    for n in /proc/sys/kernel/sched_domain/cpu*/domain0/max_interval; do echo 1 > $n; done

Testing with real-life jobs, I found I needed min_- and max_interval for
domain1 also, and a couple of other non-default values, so:

  for n in /proc/sys/kernel/sched_domain/cpu*/dom*/min_interval; do echo 0 > $n; done
  for n in /proc/sys/kernel/sched_domain/cpu*/dom*/max_interval; do echo 1 > $n; done
  echo 1000000000 > /proc/sys/kernel/sched_latency_ns 
  echo 100000 >     /proc/sys/kernel/sched_min_granularity_ns
  echo 10000 >      /proc/sys/kernel/sched_wakeup_granularity_ns

and then things seem fair and my users are happy.

Thanks, Paul

Paul Szabo   psz@...hs.usyd.edu.au   http://www.maths.usyd.edu.au/u/psz/
School of Mathematics and Statistics   University of Sydney    Australia

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