On Fri, Jul 24, 2020 at 09:14:26AM +0200, Juri Lelli wrote:
> Hi,
>
> On 07/07/20 00:04, Peng Liu wrote:
> > 'commit 840d719604b0 ("sched/deadline: Update rq_clock of later_rq when
> > pushing a task")'
> > introduced the update_rq_clock() to fix the "used-before-update" bug.
> >
> > 'commit f4904815f97a ("sched/deadline: Fix double accounting of rq/running
> > bw in push & pull")'
> > took away the bug source(add_running_bw()).
> >
> > We no longer need to update rq_clock in advance, let activate_task()
> > worry about that.
> >
> > Signed-off-by: Peng Liu <iwtba...@gmail.com>
> > ---
> > kernel/sched/deadline.c | 8 +-------
> > 1 file changed, 1 insertion(+), 7 deletions(-)
> >
> > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> > index 504d2f51b0d6..c3fa11f84d93 100644
> > --- a/kernel/sched/deadline.c
> > +++ b/kernel/sched/deadline.c
> > @@ -2104,13 +2104,7 @@ static int push_dl_task(struct rq *rq)
> >
> > deactivate_task(rq, next_task, 0);
> > set_task_cpu(next_task, later_rq->cpu);
> > -
> > - /*
> > - * Update the later_rq clock here, because the clock is used
> > - * by the cpufreq_update_util() inside __add_running_bw().
> > - */
> > - update_rq_clock(later_rq);
> > - activate_task(later_rq, next_task, ENQUEUE_NOCLOCK);
> > + activate_task(later_rq, next_task, 0);
> > ret = 1;
>
> The change looks good to me, since now add_running_bw() is called later
> by enqueue_task_dl(), but rq_clock has already been updated by core's
> enqueue_task().
>
Thanks for your time.
> Daniel, Dietmar, a second pair of eyes (since you authored the commits
> above)?
>
> I'd chage subject to something like "sched/deadline: Stop updating
> rq_clock before pushing a task".
>
> Thanks,
>
> Juri
>
