Re: [PATCH] sched: Update task->on_rq when tasks are moving between runqueues

[Olav Haugan <ohaugan@codeaurora.org>]

On 15-10-25 11:09:24, Peter Zijlstra wrote:
> On Sat, Oct 24, 2015 at 11:01:02AM -0700, Olav Haugan wrote:
> > Task->on_rq has three states:
> > 	0 - Task is not on runqueue (rq)
> > 	1 (TASK_ON_RQ_QUEUED) - Task is on rq
> > 	2 (TASK_ON_RQ_MIGRATING) - Task is on rq but in the process of being
> > 	migrated to another rq
> > 
> > When a task is moving between rqs task->on_rq state should be
> > TASK_ON_RQ_MIGRATING
> 
> Only when not holding both rq locks..

IMHO I think we should keep the state of p->on_rq updated with the correct state
all the time unless I am incorrect in what p->on_rq represent. The task
is moving between rq's and is on the rq so the state should be
TASK_ON_RQ_MIGRATING right? I do realize that the code is currently not
broken. However, in the future someone might come along and change
set_task_cpu() and the code change might rely on an accurate p->on_rq value. It
would be good design to keep this value correct.

Thanks,

-- 
.Olav

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