Messages in this thread Patch in this message |  | | Date | Thu, 16 Jan 2025 08:53:15 -0500 | | From | Phil Auld <> | | Subject | Re: [PATCH v1] sched: Mention autogroup disabled behavior |
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Hi Alejandro,
On Thu, Jan 16, 2025 at 02:06:26PM +0100 Alejandro Colomar wrote: > Hi Phil, > > > Subject: sched: Mention autogroup disabled behavior > > Please use the pathname of the modified file as a prefix: > > man/man7/sched.7: Mention autogroup disabled behavior
ack
> > On Thu, Jan 16, 2025 at 12:46:54PM +0000, Phil Auld wrote: > > The autogroup feature can be contolled at runtime when > > built into the kernel. Disabling it in this case still > > creates autogroups and still shows the autogroup membership > > for the task in /proc. The scheduler code will just not > > use the the autogroup task group. > > Would you mind showing (in the commit message) a shell session that > demonstrates this?
This is actually part of the problem. It's very hard to see this from userspace. I can show a shell session that shows that autogroup is disabled and that my task has an autogroup in /proc but determining that the autogroup is not being used not so much. (I may be missing something obvious but I could not find it).
I had to look at the kernel code:
kernel/sched/autogroup.h: static inline struct task_group * autogroup_task_group(struct task_struct *p, struct task_group *tg) { extern unsigned int sysctl_sched_autogroup_enabled; int enabled = READ_ONCE(sysctl_sched_autogroup_enabled);
if (enabled && task_wants_autogroup(p, tg)) return p->signal->autogroup->tg;
return tg; }
bool task_wants_autogroup(struct task_struct *p, struct task_group *tg) { if (tg != &root_task_group) return false; ...
}
The former being called from sched_group_fork() and sched_get_task_group().
I suppose looking at /proc/pid/cgroup and seeing it report not "0::/" is part of it since it then won't be in root task group.
To some extent any systemd based system these days is not really using autogroup at all anyway.
I can put some of the above in there or just something like:
# cat /proc/sys/kernel/sched_autogroup_enabled 0 # cat /proc/$$/autogroup /autogroup-112 nice 0
Thoughts?
Cheers, Phil
> > > This can be confusing > > to users. Add a sentence to this effect to sched.7 to > > point this out. > > > > Signed-off-by: Phil Auld <pauld@redhat.com> > > To: Alejandro Colomar <alx@kernel.org> > > Cc: <linux-man@vger.kernel.org> > > Cc: LKML <linux-kernel@vger.kernel.org> > > Thanks! > > > > > --- > > man/man7/sched.7 | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/man/man7/sched.7 b/man/man7/sched.7 > > index 71f098e48..f0a708cd7 100644 > > --- a/man/man7/sched.7 > > +++ b/man/man7/sched.7 > > @@ -724,6 +724,8 @@ in the group terminates. > > .P > > When autogrouping is enabled, all of the members of an autogroup > > are placed in the same kernel scheduler "task group". > > +When disabled the group creation happens as above, and autogroup membership > > s/disabled/&,/ > > Also, please use semantic newlines. See man-pages(7): > > $ MANWIDTH=72 man man-pages | sed -n '/Use semantic newlines/,/^$/p' > Use semantic newlines > In the source of a manual page, new sentences should be started on > new lines, long sentences should be split into lines at clause > breaks (commas, semicolons, colons, and so on), and long clauses > should be split at phrase boundaries. This convention, sometimes > known as "semantic newlines", makes it easier to see the effect of > patches, which often operate at the level of individual sentences, > clauses, or phrases. > > > Have a lovely day! > Alex > > > +is still visible in /proc, but the autogroups are not used. > > The CFS scheduler employs an algorithm that equalizes the > > distribution of CPU cycles across task groups. > > The benefits of this for interactive desktop performance > > -- > > 2.47.0 > > > > -- > <https://www.alejandro-colomar.es/>
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