mirror of https://github.com/mkerrisk/man-pages
sched.7: Rework discussion of autogroup nice value
Remove the text saying that setting the autogroup nice value always lowers the group's priority. That was actually a bug introduced in Linux 4.7. Also make it clearer that the autogroup nice value has the same meaning as the nice value set by setpriority(2). Reported-by: Mike Galbraith <efault@gmx.de> Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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@ -732,30 +732,21 @@ This file can also be used to modify the CPU bandwidth allocated
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to a task group.
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This is done by writing a number in the "nice" range to the file
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to set the task group's nice value.
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(For a discussion of the nice value, see
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.BR getpriority (2).)
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The allowed range is from +19 (low priority) to \-20 (high priority).
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Note that
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.I all
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values in this range cause a task group to be further disfavored
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by the scheduler,
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with \-20 resulting in the scheduler mildy disfavoring
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the task group and +19 greatly disfavoring it.
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.\" FIXME Regarding the previous paragraph...
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.\" My tests indicate that writing *any* value to
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.\" the autogroup file causes the task group to get a lower
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.\" priority. This somewhat surprised me, since I assumed
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.\" (based on the parallel with the process nice(2) value)
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.\" that negative values might boost the task group's priority
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.\" above a task group whose autogroup file had not been touched.
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.\" FIXME
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.\" Because of a bug introduced in Linux 4.7
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.\" (commit 2159197d66770ec01f75c93fb11dc66df81fd45b made changes
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.\" that exposed the fact that autogroup didn't call scale_load()),
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.\" it happened that *all* values in this range caused a task group
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.\" to be further disfavored by the scheduler, with \-20 resulting
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.\" in the scheduler mildy disfavoring the task group and +19 greatly
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.\" disfavoring it.
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.\"
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.\" Is this the expected behavior? I presume it is...
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.\"
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.\" But then there's a small surprise in the interface. Suppose that
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.\" the value 0 is written to the autogroup file, then this results
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.\" in the task group being significantly disfavored. But,
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.\" the nice value *shown* in the autogroup file will be the
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.\" same as if the file had not been modified. So, the user
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.\" has no way of discovering the difference. That seems odd.
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.\" Am I missing something?
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.\" A patch was posted on 23 Nov 2016
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.\" ("sched/autogroup: Fix 64bit kernel nice adjustment";
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.\" check later to see in which kernel version it lands.
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.\" FIXME Is the following correct? Does the statement need to
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.\" be more precise? (E.g., in precisely which circumstances does
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