linux-kernel - Re: scheduler nice 19 versus 'idle' behavior / static low-priority scheduling

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Date:	Fri, 30 Jan 2009 03:16:36 -0500
From:	Nathanael Hoyle <nhoyle@...letech.com>
To:	Jan Engelhardt <jengelh@...ozas.de>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: scheduler nice 19 versus 'idle' behavior / static low-priority
	scheduling

On Fri, 2009-01-30 at 02:59 -0500, Nathanael Hoyle wrote:
> On Fri, 2009-01-30 at 08:21 +0100, Jan Engelhardt wrote:
> > On Friday 2009-01-30 07:40, Nathanael Hoyle wrote:
> > >On Fri, 2009-01-30 at 07:16 +0100, Jan Engelhardt wrote:
> > >
> > >The one discussion I saw referencing SCHED_BATCH seemed to imply that it
> > >was a non-standard kernel patch by Con Kolivas in one of his -ck
> > >variants that never made it into mainline and is not being maintained.
> > >Is this inaccurate?
> > 
> > The presence of SCHED_BATCH in linux/sched.h tells me it is available
> > (on the other hand, SCHED_ISO, also from -ck, is only listed as a comment.)
> > 
> 
> Fair enough. I should have re-checked recent sources after your mention
> rather than going on the old thread I found.
> 
> > >I was unfamiliar with SCHED_IDLE. Having done a little Googling now, I
> > >finally find reference to the man page for sched_setscheduler(2). This
> > >appears that it is likely what I wanted.
> > >
> > >I think the information I had been able to find was somehwat out of
> > >date.
> > 
> > The manpage does say it, but if your local distro does not 
> > mention SCHED_BATCH/SCHED_IDLE, then that's a pretty sad distro.
> > 
> > The doc in sched_setschedule seems complete to me as of man-pages 3.13.
> > 
> > >Is there currently a standardized userspace tool to use to run a command
> > >in order to alter its scheduling class? Obviously writing one would be
> > >trivial, but didn't know if something like:
> > 
> > man chrt
> 
> The latest version of man chrt that I can find implies that it handles
> SCHED_BATCH but not SCHED_IDLE. To that end, if anyone else is
> interested, I have thrown together the above-suggested 'runidle' which
> will invoke the passed command using the SCHED_IDLE scheduler; it's
> nothing fancy.
> 
> I am running foldingathome under it at the moment, and it seems to be
> improving the situation somewhat, but I still need/want to test with
> Mike's referenced patches.
> 

<snipped old version, because of a fixed goof, and this has better
formatting for mail client>


#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sched.h>
#include <linux/sched.h>

extern char **environ;

int
main(int argc, char **argv) {
  struct sched_param sp;
  sp.sched_priority = 0;

  if(argc<2) {
    perror("Must specify at least one argument: the path to " \
      "the program to execute. Additional arguments may be " \
      "specified which will be passed to the called program.");
    return EXIT_FAILURE;
  }

  if(sched_setscheduler(0, SCHED_IDLE, &sp) == -1) {
    perror("Failed to alter scheduling class!");
    return EXIT_FAILURE;
  }

  if(argc==2) {
    if(execve(argv[1], NULL, environ) == -1) {
      perror("Failed to execve target!");
    }
  } else {
    if(execve(argv[1], argv+1, environ) == -1) {
      perror("Failed to execve target!");
    }
  }

  /* should be unreachable */
  return EXIT_FAILURE;
}

> -Nathanael

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