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 07/14] sched/core: uclamp: enforce last task UCLAMP_MAX
Date: Thu, 16 Aug 2018 17:47:45 +0100 [thread overview]
Message-ID: <20180816164745.GF2960@e110439-lin> (raw)
In-Reply-To: <2366fe11-db1f-4f39-df03-960535611319@arm.com>
On 16-Aug 17:43, Dietmar Eggemann wrote:
> On 08/06/2018 06:39 PM, Patrick Bellasi wrote:
> >When a util_max clamped task sleeps, its clamp constraints are removed
> >from the CPU. However, the blocked utilization on that CPU can still be
> >higher than the max clamp value enforced while that task was running.
> >This max clamp removal when a CPU is going to be idle could thus allow
> >unwanted CPU frequency increases, right while the task is not running.
>
> So 'rq->uclamp.flags == UCLAMP_FLAG_IDLE' means CPU is IDLE because
> non-clamped tasks are tracked as well ((group_id = 0)).
Right, but... with (group_id = 0) you mean that "non-clamped tasks are
tracked" in the first clamp group?
> Maybe this is worth mentioning here?
Maybe I can explicitely say that we detect that there are not RUNNABLE
tasks because all the clamp groups are in UCLAMP_NOT_VALID status.
> >This can happen, for example, where there is another (smaller) task
> >running on a different CPU of the same frequency domain.
> >In this case, when we aggregate the utilization of all the CPUs in a
> >shared frequency domain, schedutil can still see the full non clamped
> >blocked utilization of all the CPUs and thus eventually increase the
> >frequency.
> >
> >Let's fix this by using:
> >
> > uclamp_cpu_put_id(UCLAMP_MAX)
> > uclamp_cpu_update(last_clamp_value)
> >
> >to detect when a CPU has no more RUNNABLE clamped tasks and to flag this
> >condition. Thus, while a CPU is idle, we can still enforce the last used
> >clamp value for it.
> >
> >To the contrary, we do not track any UCLAMP_MIN since, while a CPU is
> >idle, we don't want to enforce any minimum frequency
> >Indeed, we rely just on blocked load decay to smoothly reduce the
> >frequency.
>
> [...]
>
> >diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> >index bc2beedec7bf..ff76b000bbe8 100644
> >--- a/kernel/sched/core.c
> >+++ b/kernel/sched/core.c
> >@@ -906,7 +906,8 @@ uclamp_group_find(int clamp_id, unsigned int clamp_value)
> > * For the specified clamp index, this method computes the new CPU utilization
> > * clamp to use until the next change on the set of RUNNABLE tasks on that CPU.
> > */
> >-static inline void uclamp_cpu_update(struct rq *rq, int clamp_id)
> >+static inline void uclamp_cpu_update(struct rq *rq, int clamp_id,
> >+ unsigned int last_clamp_value)
> > {
> > struct uclamp_group *uc_grp = &rq->uclamp.group[clamp_id][0];
> > int max_value = UCLAMP_NOT_VALID;
> >@@ -924,6 +925,19 @@ static inline void uclamp_cpu_update(struct rq *rq, int clamp_id)
>
> The condition:
>
> if (!uclamp_group_active(uc_grp, group_id))
> continue;
>
> in 'for (group_id = 0; group_id <= CONFIG_UCLAMP_GROUPS_COUNT; ++group_id)
> {}' makes sure that 'max_value == UCLAMP_NOT_VALID' is true for the if
> condition (*):
>
>
> > if (max_value >= SCHED_CAPACITY_SCALE)
> > break;
> > }
> >+
> >+ /*
> >+ * Just for the UCLAMP_MAX value, in case there are no RUNNABLE
> >+ * task, we keep the CPU clamped to the last task's clamp value.
> >+ * This avoids frequency spikes to MAX when one CPU, with an high
> >+ * blocked utilization, sleeps and another CPU, in the same frequency
> >+ * domain, do not see anymore the clamp on the first CPU.
> >+ */
> >+ if (clamp_id == UCLAMP_MAX && max_value == UCLAMP_NOT_VALID) {
> >+ rq->uclamp.flags |= UCLAMP_FLAG_IDLE;
> >+ max_value = last_clamp_value;
> >+ }
> >+
>
> (*): So the uc_grp[group_id].value stays last_clamp_value?
A bit confusing... but I think you've got the point.
> What do you do when the blocked utilization decays below this enforced
> last_clamp_value on that CPU?
This is done _just_ for max_util:
- it clamps a blocked utilization bigger then last_clamp_value
thus avoiding the selection of an OPP bigger then the one enforced
while the task was runnable
- it has not effect on a blocked utilization smaller then last_clamp_value
thus allowing to reduce gracefully the OPP as long as the blocked
utilization is decayed
> I assume there are plenty of this kind of corner cases because we have
> blocked signals (including all tasks) and clamping (including runnable
> tasks).
This is a pretty compelling one I've noticed in my tests and thus
worth a fix... I don't have on hand other similar corner cases, do
you?
--
#include <best/regards.h>
Patrick Bellasi
next prev parent reply other threads:[~2018-08-16 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
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 [this message]
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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