On 08-Jan 09:51, Quentin Perret wrote:
> On Tuesday 07 Jan 2020 at 20:30:36 (+0100), Dietmar Eggemann wrote:
> > On 07/01/2020 14:42, Quentin Perret wrote:
> > > Hi Qais,
> > >
> > > On Friday 20 Dec 2019 at 16:48:38 (+0000), Qais Yousef wrote:
> >
> > [...]
> >
> > >> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> > >> index e591d40fd645..19572dfc175b 100644
> > >> --- a/kernel/sched/rt.c
> > >> +++ b/kernel/sched/rt.c
> > >> @@ -2147,6 +2147,12 @@ static void pull_rt_task(struct rq *this_rq)
> > >> */
> > >> static void task_woken_rt(struct rq *rq, struct task_struct *p)
> > >> {
> > >> + /*
> > >> + * When sysctl_sched_rt_uclamp_util_min value is changed by the user,
> > >> + * we apply any new value on the next wakeup, which is here.
> > >> + */
> > >> + uclamp_rt_sync_default_util_min(p);
> > >
> > > The task has already been enqueued and sugov has been called by then I
> > > think, so this is a bit late. You could do that in uclamp_rq_inc() maybe?
No, the above sync should neven be done.
For CFS tasks is currenly working by computing the effective clamp
from core.c::enqueue_task() before calling into the scheduling class
callback.
We should use a similar approach for RT tasks thus avoiding rt.c
specific code and ensuring correct effective values are _aggregated_
out of task's _requests_ and system-wide's _constraints_ before
calling sugov.
> > That's probably better.
> > Just to be sure ...we want this feature (an existing rt task gets its
> > UCLAMP_MIN value set when the sysctl changes)
No, that's not a feature. That's an hack I would avoid.
> > because there could be rt tasks running before the sysctl is set?
>
> Yeah, I was wondering the same thing, but I'd expect sysadmin to want
> this. We could change the min clamp of existing RT tasks in userspace
> instead, but given how simple Qais' lazy update code is, the in-kernel
> looks reasonable to me. No strong opinion, though.
>
> Thanks,
> Quentin
--
#include <best/regards.h>
Patrick Bellasi
