From: Patrick Bellasi <patrick.bellasi@arm.com>
To: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>, Tejun Heo <tj@kernel.org>,
"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
Viresh Kumar <viresh.kumar@linaro.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Paul Turner <pjt@google.com>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Juri Lelli <juri.lelli@redhat.com>, Todd Kjos <tkjos@google.com>,
Joel Fernandes <joelaf@google.com>,
Steve Muckle <smuckle@google.com>,
Suren Baghdasaryan <surenb@google.com>
Subject: Re: [PATCH v3 03/14] sched/core: uclamp: add CPU's clamp groups accounting
Date: Tue, 14 Aug 2018 17:49:05 +0100 [thread overview]
Message-ID: <20180814164905.GG2605@e110439-lin> (raw)
In-Reply-To: <a24def9b-57bb-d072-5064-0421076d2e43@arm.com>
Hi Dietmar!
On 14-Aug 17:44, Dietmar Eggemann wrote:
> On 08/06/2018 06:39 PM, Patrick Bellasi wrote:
[...]
> >+/**
> >+ * uclamp_cpu_put_id(): decrease reference count for a clamp group on a CPU
> >+ * @p: the task being dequeued from a CPU
> >+ * @cpu: the CPU from where the clamp group has to be released
> >+ * @clamp_id: the utilization clamp (e.g. min or max utilization) to release
> >+ *
> >+ * When a task is dequeued from a CPU's RQ, the CPU's clamp group reference
> >+ * counted by the task is decreased.
> >+ * If this was the last task defining the current max clamp group, then the
> >+ * CPU clamping is updated to find the new max for the specified clamp
> >+ * index.
> >+ */
> >+static inline void uclamp_cpu_put_id(struct task_struct *p,
> >+ struct rq *rq, int clamp_id)
> >+{
> >+ struct uclamp_group *uc_grp;
> >+ struct uclamp_cpu *uc_cpu;
> >+ unsigned int clamp_value;
> >+ int group_id;
> >+
> >+ /* No task specific clamp values: nothing to do */
> >+ group_id = p->uclamp[clamp_id].group_id;
> >+ if (group_id == UCLAMP_NOT_VALID)
> >+ return;
> >+
> >+ /* Decrement the task's reference counted group index */
> >+ uc_grp = &rq->uclamp.group[clamp_id][0];
> >+#ifdef SCHED_DEBUG
> >+ if (unlikely(uc_grp[group_id].tasks == 0)) {
> >+ WARN(1, "invalid CPU[%d] clamp group [%d:%d] refcount\n",
> >+ cpu_of(rq), clamp_id, group_id);
> >+ uc_grp[group_id].tasks = 1;
> >+ }
> >+#endif
>
> This one indicates that there are some holes in your ref-counting.
Not really, this has been added not because I've detected a refcount
issue... but because it was suggested as a possible safety check in a
previous code review comment:
https://lore.kernel.org/lkml/20180720151156.GA31421@e110439-lin/
> It's probably easier to debug that there is still a task but the
> uc_grp[group_id].tasks value == 0 (A). I assume the other problem exists as
> well, i.e. last task and uc_grp[group_id].tasks > 1 (B)?
>
> You have uclamp_cpu_[get/put](_id)() in [enqueue/dequeue]_task.
>
> Patch 04/14 introduces its use in uclamp_task_update_active().
>
> Do you know why (A) (and (B)) are happening?
I've never saw that warning in my tests so far so, again, the warning
is there just to support testing/debugging when refcounting code
is/will be touched in the future. That's also the reason why is
SCHED_DEBUG protected.
> >+ uc_grp[group_id].tasks -= 1;
> >+
> >+ /* If this is not the last task, no updates are required */
> >+ if (uc_grp[group_id].tasks > 0)
> >+ return;
> >+
> >+ /*
> >+ * Update the CPU only if this was the last task of the group
> >+ * defining the current clamp value.
> >+ */
> >+ uc_cpu = &rq->uclamp;
> >+ clamp_value = uc_grp[group_id].value;
> >+ if (clamp_value >= uc_cpu->value[clamp_id])
>
> 'clamp_value > uc_cpu->value[clamp_id]' should indicate another
> inconsistency in the uclamp machinery, right?
Here you right, I would say that it should always be:
clamp_value <= uc_cpu->value[clamp_id]
since this matches the update done at the end of uclamp_cpu_get_id():
if (uc_cpu->value[clamp_id] < clamp_value)
uc_cpu->value[clamp_id] = clamp_value;
Perhaps we can add another safety check here, similar to the one
above, to have something like:
clamp_value = uc_grp[group_id].value;
#ifdef SCHED_DEBUG
if (unlikely(clamp_value > uc_cpu->value[clamp_id])) {
WARN(1, "invalid CPU[%d] clamp group [%d:%d] value\n",
cpu_of(rq), clamp_id, group_id);
#endif
if (clamp_value == uc_cpu->value[clamp_id])
uclamp_cpu_update(rq, clamp_id);
--
#include <best/regards.h>
Patrick Bellasi
next prev parent reply other threads:[~2018-08-14 16:49 UTC|newest]
Thread overview: 82+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-06 16:39 [PATCH v3 00/14] Add utilization clamping support Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 01/14] sched/core: uclamp: extend sched_setattr to support utilization clamping Patrick Bellasi
2018-08-06 16:50 ` Randy Dunlap
2018-08-09 8:39 ` Patrick Bellasi
2018-08-09 15:20 ` Randy Dunlap
2018-08-07 9:59 ` Juri Lelli
2018-08-13 12:14 ` Patrick Bellasi
2018-08-13 12:27 ` Juri Lelli
2018-08-07 12:35 ` Juri Lelli
2018-08-09 9:14 ` Patrick Bellasi
2018-08-09 9:50 ` Juri Lelli
2018-08-09 15:23 ` Patrick Bellasi
2018-08-10 7:50 ` Juri Lelli
2018-08-17 10:34 ` Quentin Perret
2018-08-17 10:57 ` Patrick Bellasi
2018-08-17 11:14 ` Quentin Perret
2018-08-06 16:39 ` [PATCH v3 02/14] sched/core: uclamp: map TASK's clamp values into CPU's clamp groups Patrick Bellasi
2018-08-14 11:25 ` Pavan Kondeti
2018-08-14 15:21 ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 03/14] sched/core: uclamp: add CPU's clamp groups accounting Patrick Bellasi
2018-08-14 15:44 ` Dietmar Eggemann
2018-08-14 16:49 ` Patrick Bellasi [this message]
2018-08-15 9:37 ` Dietmar Eggemann
2018-08-15 10:54 ` Patrick Bellasi
2018-08-15 10:59 ` Dietmar Eggemann
2018-08-16 13:32 ` Patrick Bellasi
2018-08-16 13:37 ` Quentin Perret
2018-08-16 13:45 ` Dietmar Eggemann
2018-08-16 14:21 ` Quentin Perret
2018-08-16 15:00 ` Dietmar Eggemann
2018-08-17 11:04 ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 04/14] sched/core: uclamp: update CPU's refcount on clamp changes Patrick Bellasi
2018-08-15 15:02 ` Dietmar Eggemann
2018-08-16 13:22 ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 05/14] sched/cpufreq: uclamp: add utilization clamping for FAIR tasks Patrick Bellasi
2018-08-08 13:18 ` Vincent Guittot
2018-08-09 15:30 ` Patrick Bellasi
2018-08-15 15:30 ` Dietmar Eggemann
2018-08-16 13:53 ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 06/14] sched/cpufreq: uclamp: add utilization clamping for RT tasks Patrick Bellasi
2018-08-07 13:26 ` Juri Lelli
2018-08-09 15:34 ` Patrick Bellasi
2018-08-09 16:03 ` Vincent Guittot
2018-08-13 10:12 ` Patrick Bellasi
2018-08-13 10:50 ` Juri Lelli
2018-08-13 12:07 ` Vincent Guittot
2018-08-13 12:09 ` Vincent Guittot
2018-08-13 12:49 ` Patrick Bellasi
2018-08-13 14:06 ` Vincent Guittot
2018-08-13 15:01 ` Patrick Bellasi
2018-08-16 10:34 ` Dietmar Eggemann
2018-08-16 13:40 ` Patrick Bellasi
2018-08-07 13:54 ` Quentin Perret
2018-08-09 15:41 ` Patrick Bellasi
2018-08-09 15:55 ` Quentin Perret
2018-08-13 10:17 ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 07/14] sched/core: uclamp: enforce last task UCLAMP_MAX Patrick Bellasi
2018-08-16 15:43 ` Dietmar Eggemann
2018-08-16 16:47 ` Patrick Bellasi
2018-08-16 17:10 ` Dietmar Eggemann
2018-08-16 17:27 ` Patrick Bellasi
2018-08-16 17:20 ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 08/14] sched/core: uclamp: extend cpu's cgroup controller Patrick Bellasi
2018-08-17 12:21 ` Dietmar Eggemann
2018-08-17 14:24 ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 09/14] sched/core: uclamp: propagate parent clamps Patrick Bellasi
2018-08-16 9:09 ` Pavan Kondeti
2018-08-16 14:07 ` Patrick Bellasi
2018-08-17 13:43 ` Dietmar Eggemann
2018-08-17 14:45 ` Patrick Bellasi
2018-08-17 15:50 ` Dietmar Eggemann
2018-08-20 10:01 ` Dietmar Eggemann
2018-08-20 12:28 ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 10/14] sched/core: uclamp: map TG's clamp values into CPU's clamp groups Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 11/14] sched/core: uclamp: use TG's clamps to restrict Task's clamps Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 12/14] sched/core: uclamp: add system default clamps Patrick Bellasi
2018-08-16 9:13 ` Pavan Kondeti
2018-08-16 14:37 ` Patrick Bellasi
2018-08-20 10:18 ` Dietmar Eggemann
2018-08-20 12:27 ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 13/14] sched/core: uclamp: update CPU's refcount on TG's clamp changes Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 14/14] sched/core: uclamp: use percentage clamp values Patrick Bellasi
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