Re: [PATCH v2 2/3] sched/fair: Skip detach and attach new group task
From: Vincent Guittot
Date: Tue May 31 2016 - 08:34:13 EST
On 31 May 2016 at 14:03, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> On Tue, May 31, 2016 at 01:55:49PM +0200, Vincent Guittot wrote:
>> Hi Yuyang,
>> On 31 May 2016 at 00:32, Yuyang Du <yuyang.du@xxxxxxxxx> wrote:
>> > Vincent reported that the first task to a new task group's cfs_rq will
>> > be attached in attach_task_cfs_rq() and once more when it is enqueued
>> > (see https://lkml.org/lkml/2016/5/25/388).
>> > Actually, it is worse, attach_task_cfs_rq() is invoked for new task even
>> > way before the new task is initiated in init_entity_runnable_average().
>> > Solve this by avoiding attach as well as detach new task in
>> > task_move_group_fair(). To do it, we need to know whether the task
>> > is forked or not, so we pass this info all the way from sched_move_task()
>> > to attach_task_cfs_rq().
>> I have tested your patch and I can't the spurious detach
>> /attach_task_cfs_rq anymore
>> so you can add my tested-by.
> Could someone update the Changelog to better explain the whole
> Because a quick look seems to suggest something like:
> ss->fork() := cpu_cgroup_fork()
> Which seems to suggest init_entity_runnable_average() is placed wrong
> and should live in sched_fork() ?
> Or am I not getting it.. ?
The sched_avg of a task is not used anymore in copy_process with
yuyang's patchset. To be fully correct, we still have a
p->se.avg.last_update_time = 0 in cpu_cgroup_fork but this is just the
side effect of factoring cpu_group_fork and cpu_group_move in
sched_move_task and it will be overwritten by
init_entity_runnable_average before being used.
Now, cpu_cgroup_fork() only sets task group and cfs_rq of the forked task
ss->fork() := cpu_cgroup_fork() which only set task group and
cfs_rq of the sched_entity of the task