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From: Quentin Perret <quentin.perret@arm.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: peterz@infradead.org, rjw@rjwysocki.net,
	linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
	gregkh@linuxfoundation.org, mingo@redhat.com,
	dietmar.eggemann@arm.com, morten.rasmussen@arm.com,
	chris.redpath@arm.com, patrick.bellasi@arm.com,
	valentin.schneider@arm.com, vincent.guittot@linaro.org,
	thara.gopinath@linaro.org, viresh.kumar@linaro.org,
	tkjos@google.com, joel@joelfernandes.org, smuckle@google.com,
	adharmap@codeaurora.org, skannan@codeaurora.org,
	pkondeti@codeaurora.org, juri.lelli@redhat.com,
	edubezval@gmail.com, srinivas.pandruvada@linux.intel.com,
	currojerez@riseup.net, javi.merino@kernel.org
Subject: Re: [PATCH v10 04/15] PM / EM: Expose the Energy Model in sysfs
Date: Tue, 11 Dec 2018 15:04:11 +0000	[thread overview]
Message-ID: <20181211150409.vn25xlmzonqhd4fi@queper01-lin> (raw)
In-Reply-To: <20181211141827.GA85618@gmail.com>

On Tuesday 11 Dec 2018 at 15:18:28 (+0100), Ingo Molnar wrote:
> 
> * Quentin Perret <quentin.perret@arm.com> wrote:
> 
> > Expose the Energy Model (read-only) of all performance domains in sysfs
> > for convenience. To do so, add a kobject to the CPU subsystem under the
> > umbrella of which a kobject for each performance domain is attached.
> > 
> > The resulting hierarchy is as follows for a platform with two
> > performance domains for example:
> > 
> >    /sys/devices/system/cpu/energy_model
> >    ├── pd0
> >    │   ├── cost
> >    │   ├── cpus
> >    │   ├── frequency
> >    │   └── power
> >    └── pd4
> >        ├── cost
> >        ├── cpus
> >        ├── frequency
> >        └── power
> > 
> > In this implementation, the kobject abstraction is only used as a
> > convenient way of exposing data to sysfs. However, it could also be
> > used in the future to allocate and release performance domains in a more
> > dynamic way using reference counting.
> > 
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> > Signed-off-by: Quentin Perret <quentin.perret@arm.com>
> > ---
> >  include/linux/energy_model.h |  2 +
> >  kernel/power/energy_model.c  | 90 ++++++++++++++++++++++++++++++++++++
> >  2 files changed, 92 insertions(+)
> 
> Why is a read-only ABI added for 'convenience'? We really don't do that 
> as ABIs are final and they come with responsibilities.
> 
> I think if this is for debug purposes it should be declared and put into 
> debugfs or so.
> 
> If it's for some other purpose that purpose should be declared.

This is basically supposed to look like the CPUFreq policy entries.
You can get things like this for CPUFreq:

  $ cat /sys/devices/system/cpu/cpufreq/policy1/scaling_available_frequencies
  450000 625000 800000 950000 1100000

And things like this for the EM:

$ cat /sys/devices/system/cpu/energy_model/pd1/power
  160 239 343 454 583

In general, I expect these two interfaces to be used for similar
purposes. Now, whether or not they should be exposed in debugfs is a
good question. I went for sysfs for consistency with CPUFreq, but I'm
not opposed to a change in this area for the EM if you feel it's
preferable.

Also, I'm happy to just drop this patch for now and to begin by not
exposing the EM at all. It's easier to expose it later than to remove it
once userspace tools depend on it.

Thanks,
Quentin

  reply	other threads:[~2018-12-11 15:04 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-03  9:56 [PATCH v10 00/15] Energy Aware Scheduling Quentin Perret
2018-12-03  9:56 ` [PATCH v10 01/15] sched: Relocate arch_scale_cpu_capacity Quentin Perret
2018-12-11 15:32   ` [tip:sched/core] sched/topology: Relocate arch_scale_cpu_capacity() to the internal header tip-bot for Quentin Perret
2018-12-03  9:56 ` [PATCH v10 02/15] sched/cpufreq: Prepare schedutil for Energy Aware Scheduling Quentin Perret
2018-12-11 12:01   ` Rafael J. Wysocki
2018-12-11 12:17     ` Quentin Perret
2018-12-11 12:22       ` Rafael J. Wysocki
2018-12-11 12:24         ` Quentin Perret
2018-12-11 15:33   ` [tip:sched/core] " tip-bot for Quentin Perret
2018-12-03  9:56 ` [PATCH v10 03/15] PM: Introduce an Energy Model management framework Quentin Perret
2018-12-11 15:33   ` [tip:sched/core] " tip-bot for Quentin Perret
2018-12-03  9:56 ` [PATCH v10 04/15] PM / EM: Expose the Energy Model in sysfs Quentin Perret
2018-12-11 14:18   ` Ingo Molnar
2018-12-11 15:04     ` Quentin Perret [this message]
2018-12-03  9:56 ` [PATCH v10 05/15] sched/topology: Reference the Energy Model of CPUs when available Quentin Perret
2018-12-11 15:34   ` [tip:sched/core] " tip-bot for Quentin Perret
2018-12-03  9:56 ` [PATCH v10 06/15] sched/topology: Lowest CPU asymmetry sched_domain level pointer Quentin Perret
2018-12-11 15:34   ` [tip:sched/core] sched/topology: Add lowest " tip-bot for Quentin Perret
2018-12-03  9:56 ` [PATCH v10 07/15] sched/topology: Disable EAS on inappropriate platforms Quentin Perret
2018-12-11 15:35   ` [tip:sched/core] " tip-bot for Quentin Perret
2018-12-03  9:56 ` [PATCH v10 08/15] sched/topology: Make Energy Aware Scheduling depend on schedutil Quentin Perret
2018-12-11 15:36   ` [tip:sched/core] " tip-bot for Quentin Perret
2018-12-03  9:56 ` [PATCH v10 09/15] sched: Introduce sched_energy_present static key Quentin Perret
2018-12-11 15:36   ` [tip:sched/core] sched/toplogy: Introduce the 'sched_energy_present' " tip-bot for Quentin Perret
2018-12-13 13:56     ` Quentin Perret
2018-12-03  9:56 ` [PATCH v10 10/15] sched: Introduce a sysctl for Energy Aware Scheduling Quentin Perret
2018-12-11 14:15   ` Ingo Molnar
2018-12-11 14:49     ` Quentin Perret
2018-12-13 14:03       ` Peter Zijlstra
2019-01-21 11:35   ` [tip:sched/core] sched/topology: " tip-bot for Quentin Perret
2019-01-21 13:51   ` tip-bot for Quentin Perret
2019-01-27 11:34   ` tip-bot for Quentin Perret
2018-12-03  9:56 ` [PATCH v10 11/15] sched/fair: Clean-up update_sg_lb_stats parameters Quentin Perret
2018-12-11 15:37   ` [tip:sched/core] " tip-bot for Quentin Perret
2018-12-03  9:56 ` [PATCH v10 12/15] sched: Add over-utilization/tipping point indicator Quentin Perret
2018-12-11 15:37   ` [tip:sched/core] sched/fair: " tip-bot for Morten Rasmussen
2018-12-03  9:56 ` [PATCH v10 13/15] sched/fair: Introduce an energy estimation helper function Quentin Perret
2018-12-11 15:38   ` [tip:sched/core] " tip-bot for Quentin Perret
2018-12-03  9:56 ` [PATCH v10 14/15] sched/fair: Select an energy-efficient CPU on task wake-up Quentin Perret
2018-12-11 15:39   ` [tip:sched/core] " tip-bot for Quentin Perret
2018-12-03  9:56 ` [PATCH v10 15/15] OPTIONAL: cpufreq: dt: Register an Energy Model Quentin Perret
2019-01-08 20:38   ` Matthias Kaehlcke
2019-01-09 10:57     ` Quentin Perret
2019-01-09 18:14       ` Matthias Kaehlcke
2019-01-10  9:08         ` Quentin Perret

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