From: Peter Zijlstra <peterz@infradead.org>
To: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
linux-api@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
Tejun Heo <tj@kernel.org>,
"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Viresh Kumar <viresh.kumar@linaro.org>,
Paul Turner <pjt@google.com>,
Quentin Perret <quentin.perret@arm.com>,
Dietmar Eggemann <dietmar.eggemann@arm.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 v6 04/16] sched/core: uclamp: Add CPU's clamp buckets refcounting
Date: Tue, 22 Jan 2019 11:03:42 +0100 [thread overview]
Message-ID: <20190122100342.GO27931@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190121155407.gv4cxpg2njqmdlj5@e110439-lin>
On Mon, Jan 21, 2019 at 03:54:07PM +0000, Patrick Bellasi wrote:
> On 21-Jan 16:17, Peter Zijlstra wrote:
> > On Tue, Jan 15, 2019 at 10:15:01AM +0000, Patrick Bellasi wrote:
> > > +#ifdef CONFIG_UCLAMP_TASK
> >
> > > +struct uclamp_bucket {
> > > + unsigned long value : bits_per(SCHED_CAPACITY_SCALE);
> > > + unsigned long tasks : BITS_PER_LONG - bits_per(SCHED_CAPACITY_SCALE);
> > > +};
> >
> > > +struct uclamp_cpu {
> > > + unsigned int value;
> >
> > /* 4 byte hole */
> >
> > > + struct uclamp_bucket bucket[UCLAMP_BUCKETS];
> > > +};
> >
> > With the default of 5, this UCLAMP_BUCKETS := 6, so struct uclamp_cpu
> > ends up being 7 'unsigned long's, or 56 bytes on 64bit (with a 4 byte
> > hole).
>
> Yes, that's dimensioned and configured to fit into a single cache line
> for all the possible 5 (by default) clamp values of a clamp index
> (i.e. min or max util).
And I suppose you picked 5 because 20% is a 'nice' number? whereas
16./666/% is a bit odd?
> > > +#endif /* CONFIG_UCLAMP_TASK */
> > > +
> > > /*
> > > * This is the main, per-CPU runqueue data structure.
> > > *
> > > @@ -835,6 +879,11 @@ struct rq {
> > > unsigned long nr_load_updates;
> > > u64 nr_switches;
> > >
> > > +#ifdef CONFIG_UCLAMP_TASK
> > > + /* Utilization clamp values based on CPU's RUNNABLE tasks */
> > > + struct uclamp_cpu uclamp[UCLAMP_CNT] ____cacheline_aligned;
> >
> > Which makes this 112 bytes with 8 bytes in 2 holes, which is short of 2
> > 64 byte cachelines.
>
> Right, we have 2 cache lines where:
> - the first $L tracks 5 different util_min values
> - the second $L tracks 5 different util_max values
Well, not quite so, if you want that you should put
____cacheline_aligned on struct uclamp_cpu. Such that the individual
array entries are each aligned, the above only alignes the whole array,
so the second uclamp_cpu is spread over both lines.
But I think this is actually better, since you have to scan both
min/max anyway, and allowing one the straddle a line you have to touch
anyway, allows for using less lines in total.
Consider for example the case where UCLAMP_BUCKETS=8, then each
uclamp_cpu would be 9 words or 72 bytes. If you force align the member,
then you end up with 4 lines, whereas now it would be 3.
> > Is that the best layout?
>
> It changed few times and that's what I found more reasonable for both
> for fitting the default configuration and also for code readability.
> Notice that we access RQ and SE clamp values with the same patter,
> for example:
>
> {rq|p}->uclamp[clamp_idx].value
>
> Are you worried about the holes or something else specific ?
Not sure; just mostly asking if this was by design or by accident.
One thing I did wonder though; since bucket[0] is counting the tasks
that are unconstrained and it's bucket value is basically fixed (0 /
1024), can't we abuse that value field to store uclamp_cpu::value ?
OTOH, doing that might make the code really ugly with all them:
if (!bucket_id)
exceptions all over the place.
next prev parent reply other threads:[~2019-01-22 10:03 UTC|newest]
Thread overview: 89+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-15 10:14 [PATCH v6 00/16] Add utilization clamping support Patrick Bellasi
2019-01-15 10:14 ` [PATCH v6 01/16] sched/core: Allow sched_setattr() to use the current policy Patrick Bellasi
2019-01-25 13:56 ` Alessio Balsini
2019-01-15 10:14 ` [PATCH v6 02/16] sched/core: uclamp: Extend sched_setattr() to support utilization clamping Patrick Bellasi
2019-01-15 10:15 ` [PATCH v6 03/16] sched/core: uclamp: Map TASK's clamp values into CPU's clamp buckets Patrick Bellasi
2019-01-21 10:15 ` Peter Zijlstra
2019-01-21 12:27 ` Patrick Bellasi
2019-01-21 12:51 ` Peter Zijlstra
2019-01-21 15:05 ` Peter Zijlstra
2019-01-21 15:34 ` Patrick Bellasi
2019-01-15 10:15 ` [PATCH v6 04/16] sched/core: uclamp: Add CPU's clamp buckets refcounting Patrick Bellasi
2019-01-21 14:59 ` Peter Zijlstra
2019-01-21 15:23 ` Patrick Bellasi
2019-01-21 16:12 ` Peter Zijlstra
2019-01-21 16:33 ` Patrick Bellasi
2019-01-22 9:45 ` Peter Zijlstra
2019-01-22 10:31 ` Patrick Bellasi
2019-01-21 15:17 ` Peter Zijlstra
2019-01-21 15:54 ` Patrick Bellasi
2019-01-22 10:03 ` Peter Zijlstra [this message]
2019-01-22 10:53 ` Patrick Bellasi
2019-01-15 10:15 ` [PATCH v6 05/16] sched/core: uclamp: Update CPU's refcount on clamp changes Patrick Bellasi
2019-01-21 15:33 ` Peter Zijlstra
2019-01-21 15:44 ` Patrick Bellasi
2019-01-22 9:37 ` Peter Zijlstra
2019-01-22 10:43 ` Patrick Bellasi
2019-01-22 13:28 ` Peter Zijlstra
2019-01-22 14:01 ` Patrick Bellasi
2019-01-22 14:57 ` Peter Zijlstra
2019-01-22 15:33 ` Patrick Bellasi
2019-01-23 9:16 ` Peter Zijlstra
2019-01-23 14:14 ` Patrick Bellasi
2019-01-23 18:59 ` Peter Zijlstra
2019-01-24 11:21 ` Patrick Bellasi
2019-01-24 12:38 ` Peter Zijlstra
2019-01-15 10:15 ` [PATCH v6 06/16] sched/core: uclamp: Enforce last task UCLAMP_MAX Patrick Bellasi
2019-01-15 10:15 ` [PATCH v6 07/16] sched/core: uclamp: Add system default clamps Patrick Bellasi
2019-01-22 13:56 ` Peter Zijlstra
2019-01-22 14:43 ` Patrick Bellasi
2019-01-22 15:13 ` Peter Zijlstra
2019-01-22 15:41 ` Patrick Bellasi
2019-01-23 9:22 ` Peter Zijlstra
2019-01-23 14:19 ` Patrick Bellasi
2019-01-23 19:10 ` Peter Zijlstra
2019-01-15 10:15 ` [PATCH v6 08/16] sched/cpufreq: uclamp: Add utilization clamping for FAIR tasks Patrick Bellasi
2019-01-22 10:37 ` Rafael J. Wysocki
2019-01-22 11:02 ` Patrick Bellasi
2019-01-22 11:04 ` Rafael J. Wysocki
2019-01-22 11:27 ` Patrick Bellasi
2019-01-22 15:21 ` Peter Zijlstra
2019-01-22 15:45 ` Patrick Bellasi
2019-01-22 17:13 ` Peter Zijlstra
2019-01-22 18:18 ` Patrick Bellasi
2019-01-23 9:52 ` Peter Zijlstra
2019-01-23 14:24 ` Patrick Bellasi
2019-01-15 10:15 ` [PATCH v6 09/16] sched/cpufreq: uclamp: Add utilization clamping for RT tasks Patrick Bellasi
2019-01-22 12:30 ` Quentin Perret
2019-01-22 12:37 ` Patrick Bellasi
2019-01-23 10:28 ` Peter Zijlstra
2019-01-23 14:33 ` Patrick Bellasi
2019-01-23 10:49 ` Peter Zijlstra
2019-01-23 14:40 ` Patrick Bellasi
2019-01-23 20:11 ` Peter Zijlstra
2019-01-24 12:30 ` Patrick Bellasi
2019-01-24 12:38 ` Patrick Bellasi
2019-01-24 15:12 ` Peter Zijlstra
2019-01-24 16:00 ` Patrick Bellasi
2019-01-24 15:31 ` Peter Zijlstra
2019-01-24 16:14 ` Patrick Bellasi
2019-01-24 15:33 ` Peter Zijlstra
2019-01-24 15:15 ` Peter Zijlstra
2019-01-24 16:05 ` Patrick Bellasi
2019-01-15 10:15 ` [PATCH v6 10/16] sched/core: Add uclamp_util_with() Patrick Bellasi
2019-01-23 13:33 ` Peter Zijlstra
2019-01-23 14:51 ` Patrick Bellasi
2019-01-23 19:22 ` Peter Zijlstra
2019-01-15 10:15 ` [PATCH v6 11/16] sched/fair: Add uclamp support to energy_compute() Patrick Bellasi
2019-01-22 12:13 ` Quentin Perret
2019-01-22 12:45 ` Patrick Bellasi
2019-01-22 13:29 ` Quentin Perret
2019-01-22 14:26 ` Patrick Bellasi
2019-01-22 14:39 ` Quentin Perret
2019-01-22 15:01 ` Patrick Bellasi
2019-01-22 15:14 ` Quentin Perret
2019-01-15 10:15 ` [PATCH v6 12/16] sched/core: uclamp: Extend CPU's cgroup controller Patrick Bellasi
2019-01-15 10:15 ` [PATCH v6 13/16] sched/core: uclamp: Propagate parent clamps Patrick Bellasi
2019-01-15 10:15 ` [PATCH v6 14/16] sched/core: uclamp: Map TG's clamp values into CPU's clamp buckets Patrick Bellasi
2019-01-15 10:15 ` [PATCH v6 15/16] sched/core: uclamp: Use TG's clamps to restrict TASK's clamps Patrick Bellasi
2019-01-15 10:15 ` [PATCH v6 16/16] sched/core: uclamp: Update CPU's refcount on TG's clamp changes Patrick Bellasi
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