75 lines
2.7 KiB
Diff
75 lines
2.7 KiB
Diff
commit ca69daf45f94fda061f796efcc4f24ca76d8e380
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Author: Phil Auld <pauld@redhat.com>
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Date: Thu Jan 16 14:37:47 2025 +0000
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man/man7/sched.7: Mention autogroup disabled behavior
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The autogroup feature can be contolled at runtime when built into the
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kernel. Disabling it in this case still creates autogroups and still
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shows the autogroup membership for the task in /proc. The scheduler
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code will just not use the the autogroup task group. This can be
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confusing to users. Add a sentence to this effect to sched.7 to point
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this out.
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The kernel code shows how this is used. The sched_autogroup_enabled
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toggle is only used in one place.
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kernel/sched/autogroup.h:
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static inline struct task_group *
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autogroup_task_group(struct task_struct *p, struct task_group *tg)
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{
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extern unsigned int sysctl_sched_autogroup_enabled;
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int enabled = READ_ONCE(sysctl_sched_autogroup_enabled);
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if (enabled && task_wants_autogroup(p, tg))
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return p->signal->autogroup->tg;
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return tg;
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}
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task_wants_autogroup() is in kernel/sched/autogroup.c:
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bool task_wants_autogroup(struct task_struct *p, struct task_group *tg)
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{
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if (tg != &root_task_group)
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return false;
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...
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return true;
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}
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One can see that any group set other than root also bypasses the use of
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the autogroup. All of the machinery around the creation of the
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autogroup is not effected by the toggle.
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From userspace:
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0
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/autogroup-112 nice 0
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Note, systemd based system these days is not really using autogroups at
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all anyway because any task in a non-root cgroup bypasses the autogroup
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as well.
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Cc: Carlos O'Donell <codonell@redhat.com>
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Signed-off-by: Phil Auld <pauld@redhat.com>
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Message-ID: <20250116143747.2366152-1-pauld@redhat.com>
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Signed-off-by: Alejandro Colomar <alx@kernel.org>
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diff --git a/man7/sched.7 b/man/man7/sched.7
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index 71f098e48..fb8a69918 100644
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--- a/man7/sched.7
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+++ b/man7/sched.7
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@@ -724,6 +724,11 @@ in the group terminates.
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.P
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When autogrouping is enabled, all of the members of an autogroup
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are placed in the same kernel scheduler "task group".
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+When disabled,
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+the group creation happens as above,
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+and autogroup membership is still visible in
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+.IR /proc ,
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+but the autogroups are not used.
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The CFS scheduler employs an algorithm that equalizes the
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distribution of CPU cycles across task groups.
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The benefits of this for interactive desktop performance
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