Vincent Guittot b5a9b34078 sched/fair: Fix incorrect task group ->load_avg ... A scheduler performance regression has been reported by Joseph Salisbury, which he bisected back to: 3d30544f02 ("sched/fair: Apply more PELT fixes) The regression triggers when several levels of task groups are involved (read: SystemD) and cpu_possible_mask != cpu_present_mask. The root cause is that group entity's load (tg_child->se[i]->avg.load_avg) is initialized to scale_load_down(se->load.weight). During the creation of a child task group, its group entities on possible CPUs are attached to parent's cfs_rq (tg_parent) and their loads are added to the parent's load (tg_parent->load_avg) with update_tg_load_avg(). But only the load on online CPUs will then be updated to reflect real load, whereas load on other CPUs will stay at the initial value. The result is a tg_parent->load_avg that is higher than the real load, the weight of group entities (tg_parent->se[i]->load.weight) on online CPUs is smaller than it should be, and the task group gets a less running time than what it could expect. ( This situation can be detected with /proc/sched_debug. The ".tg_load_avg" of the task group will be much higher than sum of ".tg_load_avg_contrib" of online cfs_rqs of the task group. ) The load of group entities don't have to be intialized to something else than 0 because their load will increase when an entity is attached. Reported-by: Joseph Salisbury <joseph.salisbury@canonical.com> Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: <stable@vger.kernel.org> # 4.8.x Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: joonwoop@codeaurora.org Fixes: 3d30544f02 ("sched/fair: Apply more PELT fixes) Link: http://lkml.kernel.org/r/1476881123-10159-1-git-send-email-vincent.guittot@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>		2016-10-19 15:04:47 +02:00
..
auto_group.c
auto_group.h
clock.c
completion.c
core.c	Merge branch 'x86-asm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip	2016-10-03 16:13:28 -07:00
cpuacct.c
cpuacct.h
cpudeadline.c
cpudeadline.h
cpufreq_schedutil.c
cpufreq.c
cpupri.c
cpupri.h
cputime.c	sched/irqtime: Consolidate irqtime flushing code	2016-09-30 11:46:41 +02:00
deadline.c	Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip	2016-10-03 13:39:00 -07:00
debug.c	Merge branch 'for-4.9' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup	2016-10-14 12:18:50 -07:00
fair.c	sched/fair: Fix incorrect task group ->load_avg	2016-10-19 15:04:47 +02:00
features.h
idle_task.c	sched/core: Rewrite and improve select_idle_siblings()	2016-09-30 11:03:09 +02:00
idle.c	nmi_backtrace: generate one-line reports for idle cpus	2016-10-07 18:46:30 -07:00
loadavg.c
Makefile
rt.c
sched.h	Merge branch 'x86-asm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip	2016-10-03 16:13:28 -07:00
stats.c
stats.h
stop_task.c
swait.c
wait.c	sched/wait: Introduce init_wait_entry()	2016-09-30 10:54:03 +02:00