CFS scheduler unfairly prefers pinned tasks

From	paul.szabo@sydney.edu.au
Newsgroups	linux.kernel
Subject	CFS scheduler unfairly prefers pinned tasks
Date	2015-10-06 00:00 +0200
Message-ID	<qglXB-37e-27@gated-at.bofh.it> (permalink)
Organization	linux.* mail to news gateway

Show all headers | View raw

The Linux CFS scheduler prefers pinned tasks and unfairly
gives more CPU time to tasks that have set CPU affinity.
This effect is observed with or without CGROUP controls.

To demonstrate: on an otherwise idle machine, as some user
run several processes pinned to each CPU, one for each CPU
(as many as CPUs present in the system) e.g. for a quad-core
non-HyperThreaded machine:

  taskset -c 0 perl -e 'while(1){1}' &
  taskset -c 1 perl -e 'while(1){1}' &
  taskset -c 2 perl -e 'while(1){1}' &
  taskset -c 3 perl -e 'while(1){1}' &

and (as that same or some other user) run some without
pinning:

  perl -e 'while(1){1}' &
  perl -e 'while(1){1}' &

and use e.g.   top   to observe that the pinned processes get
more CPU time than "fair".

Fairness is obtained when either:
 - there are as many un-pinned processes as CPUs; or
 - with CGROUP controls and the two kinds of processes run by
   different users, when there is just one un-pinned process; or
 - if the pinning is turned off for these processes (or they
   are started without).

Any insight is welcome!

---

I would appreciate replies direct to me as I am not subscribed to the
linux-kernel mailing list (but will try to watch the archives).

This bug is also reported to Debian, please see
  http://bugs.debian.org/800945

I use Debian with the 3.16 kernel, have not yet tried 4.* kernels.


Thanks, Paul

Paul Szabo   psz@maths.usyd.edu.au   http://www.maths.usyd.edu.au/u/psz/
School of Mathematics and Statistics   University of Sydney    Australia
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Next in thread | Find similar | Unroll thread

Thread

CFS scheduler unfairly prefers pinned tasks paul.szabo@sydney.edu.au - 2015-10-06 00:00 +0200
  Re: CFS scheduler unfairly prefers pinned tasks Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-06 04:50 +0200
    Re: CFS scheduler unfairly prefers pinned tasks paul.szabo@sydney.edu.au - 2015-10-06 12:10 +0200
      Re: CFS scheduler unfairly prefers pinned tasks Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-06 14:20 +0200
        Re: CFS scheduler unfairly prefers pinned tasks paul.szabo@sydney.edu.au - 2015-10-06 22:50 +0200
          Re: CFS scheduler unfairly prefers pinned tasks Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-07 03:30 +0200
    Re: CFS scheduler unfairly prefers pinned tasks Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-08 10:30 +0200
      Re: CFS scheduler unfairly prefers pinned tasks paul.szabo@sydney.edu.au - 2015-10-08 13:00 +0200
        Re: CFS scheduler unfairly prefers pinned tasks Peter Zijlstra <peterz@infradead.org> - 2015-10-08 13:30 +0200
          [patch] sched: disable task group re-weighting on the desktop Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-10 15:30 +0200
            Re: [patch] sched: disable task group re-weighting on the desktop Peter Zijlstra <peterz@infradead.org> - 2015-10-10 19:10 +0200
              Re: [patch] sched: disable task group re-weighting on the desktop Peter Zijlstra <peterz@infradead.org> - 2015-10-10 19:20 +0200
              Re: [patch] sched: disable task group re-weighting on the desktop Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-11 04:30 +0200
                4.3 group scheduling regression Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-11 19:50 +0200
                Re: 4.3 group scheduling regression Peter Zijlstra <peterz@infradead.org> - 2015-10-12 09:30 +0200
                Re: 4.3 group scheduling regression Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-12 09:50 +0200
                Re: 4.3 group scheduling regression Peter Zijlstra <peterz@infradead.org> - 2015-10-12 10:10 +0200
                Re: 4.3 group scheduling regression Yuyang Du <yuyang.du@intel.com> - 2015-10-12 10:50 +0200
                Re: 4.3 group scheduling regression Peter Zijlstra <peterz@infradead.org> - 2015-10-12 11:20 +0200
                Re: 4.3 group scheduling regression Yuyang Du <yuyang.du@intel.com> - 2015-10-12 12:10 +0200
                Re: 4.3 group scheduling regression Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-12 12:30 +0200
                Re: 4.3 group scheduling regression Yuyang Du <yuyang.du@intel.com> - 2015-10-13 05:50 +0200
                Re: 4.3 group scheduling regression Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-13 06:10 +0200
                Re: 4.3 group scheduling regression Yuyang Du <yuyang.du@intel.com> - 2015-10-13 06:40 +0200
                Re: 4.3 group scheduling regression Peter Zijlstra <peterz@infradead.org> - 2015-10-13 10:10 +0200
                Re: 4.3 group scheduling regression Peter Zijlstra <peterz@infradead.org> - 2015-10-13 10:20 +0200
                Re: 4.3 group scheduling regression Yuyang Du <yuyang.du@intel.com> - 2015-10-13 10:30 +0200
                Re: 4.3 group scheduling regression Yuyang Du <yuyang.du@intel.com> - 2015-10-13 10:30 +0200
                Re: 4.3 group scheduling regression Peter Zijlstra <peterz@infradead.org> - 2015-10-12 13:50 +0200
                Re: 4.3 group scheduling regression Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-13 04:30 +0200
                Re: 4.3 group scheduling regression Yuyang Du <yuyang.du@intel.com> - 2015-10-13 05:30 +0200
                Re: 4.3 group scheduling regression Peter Zijlstra <peterz@infradead.org> - 2015-10-13 10:10 +0200
                Re: 4.3 group scheduling regression Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-12 10:50 +0200
            Re: [patch] sched: disable task group re-weighting on the desktop paul.szabo@sydney.edu.au - 2015-10-10 22:20 +0200
              Re: [patch] sched: disable task group re-weighting on the desktop Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-11 04:40 +0200
                Re: [patch] sched: disable task group re-weighting on the desktop paul.szabo@sydney.edu.au - 2015-10-11 11:30 +0200
                Re: [patch] sched: disable task group re-weighting on the desktop Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-11 15:00 +0200
            Re: [patch] sched: disable task group re-weighting on the desktop paul.szabo@sydney.edu.au - 2015-10-11 21:50 +0200
              Re: [patch] sched: disable task group re-weighting on the desktop Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-12 04:00 +0200
        Re: CFS scheduler unfairly prefers pinned tasks Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-08 16:30 +0200
          Re: CFS scheduler unfairly prefers pinned tasks paul.szabo@sydney.edu.au - 2015-10-09 00:00 +0200
            Re: CFS scheduler unfairly prefers pinned tasks Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-09 04:00 +0200
            Re: CFS scheduler unfairly prefers pinned tasks Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-10-09 04:50 +0200
              Re: CFS scheduler unfairly prefers pinned tasks paul.szabo@sydney.edu.au - 2015-10-11 11:50 +0200
      Re: CFS scheduler unfairly prefers pinned tasks Wanpeng Li <wanpeng.li@hotmail.com> - 2015-10-10 06:10 +0200
        Re: CFS scheduler unfairly prefers pinned tasks Wanpeng Li <wanpeng.li@hotmail.com> - 2015-10-10 10:00 +0200

csiph-web