Messages in this thread | | | Date | Wed, 24 Jun 2020 11:36:19 +0100 | From | Qais Yousef <> | Subject | Re: [PATCH v2 1/2] sched/uclamp: Fix initialization of strut uclamp_rq |
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On 06/24/20 09:26, Patrick Bellasi wrote: > > Hi Qais, > > On Fri, Jun 19, 2020 at 19:20:10 +0200, Qais Yousef <qais.yousef@arm.com> wrote... > > > struct uclamp_rq was zeroed out entirely in assumption that in the first > > call to uclamp_rq_inc() they'd be initialized correctly in accordance to > > default settings. > > > > But when next patch introduces a static key to skip > > uclamp_rq_{inc,dec}() until userspace opts in to use uclamp, schedutil > > will fail to perform any frequency changes because the > > rq->uclamp[UCLAMP_MAX].value is zeroed at init and stays as such. Which > > means all rqs are capped to 0 by default. > > Does not this means the problem is more likely with uclamp_rq_util_with(), > which should be guarded?
The initialization is wrong and needs to be fixed, no? So I won't say uclamp_rq_util_with() has any problem.
For RT boosting to work as-is, uclamp_rq_util_with() needs to stay the same, otherwise we need to add extra logic to deal with that. Which I don't think is worth it or necessary. The function is called from sugov and find_energy_efficient_cpu(), both of which aren't a worry to make this call unconditionally IMO.
Thanks
-- Qais Yousef
> > Otherwise, we will also keep doing useless min/max aggregations each > time schedutil calls that function, thus not completely removing > uclamp overheads while user-space has not opted in. > > What about dropping this and add the guard in the following patch, along > with the others?
> > > Fix it by making sure we do proper initialization at init without > > > > > Fix it by making sure we do proper initialization at init without > > relying on uclamp_rq_inc() doing it later. > > > > Fixes: 69842cba9ace ("sched/uclamp: Add CPU's clamp buckets refcounting") > > Signed-off-by: Qais Yousef <qais.yousef@arm.com> > > Cc: Juri Lelli <juri.lelli@redhat.com> > > Cc: Vincent Guittot <vincent.guittot@linaro.org> > > Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> > > Cc: Steven Rostedt <rostedt@goodmis.org> > > Cc: Ben Segall <bsegall@google.com> > > Cc: Mel Gorman <mgorman@suse.de> > > CC: Patrick Bellasi <patrick.bellasi@matbug.net> > > Cc: Chris Redpath <chris.redpath@arm.com> > > Cc: Lukasz Luba <lukasz.luba@arm.com> > > Cc: linux-kernel@vger.kernel.org > > --- > > kernel/sched/core.c | 23 ++++++++++++++++++----- > > 1 file changed, 18 insertions(+), 5 deletions(-) > > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > index a43c84c27c6f..4265861e13e9 100644 > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -1248,6 +1248,22 @@ static void uclamp_fork(struct task_struct *p) > > } > > } > > > > +static void __init init_uclamp_rq(struct rq *rq) > > +{ > > + enum uclamp_id clamp_id; > > + struct uclamp_rq *uc_rq = rq->uclamp; > > + > > + for_each_clamp_id(clamp_id) { > > + memset(uc_rq[clamp_id].bucket, > > + 0, > > + sizeof(struct uclamp_bucket)*UCLAMP_BUCKETS); > > + > > + uc_rq[clamp_id].value = uclamp_none(clamp_id); > > + } > > + > > + rq->uclamp_flags = 0; > > +} > > + > > static void __init init_uclamp(void) > > { > > struct uclamp_se uc_max = {}; > > @@ -1256,11 +1272,8 @@ static void __init init_uclamp(void) > > > > mutex_init(&uclamp_mutex); > > > > - for_each_possible_cpu(cpu) { > > - memset(&cpu_rq(cpu)->uclamp, 0, > > - sizeof(struct uclamp_rq)*UCLAMP_CNT); > > - cpu_rq(cpu)->uclamp_flags = 0; > > - } > > + for_each_possible_cpu(cpu) > > + init_uclamp_rq(cpu_rq(cpu)); > > > > for_each_clamp_id(clamp_id) { > > uclamp_se_set(&init_task.uclamp_req[clamp_id], >
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