From: Quentin Perret <quentin.perret@arm.com>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
Peter Zijlstra <peterz@infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux PM <linux-pm@vger.kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Ingo Molnar <mingo@redhat.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Chris Redpath <chris.redpath@arm.com>,
Patrick Bellasi <patrick.bellasi@arm.com>,
Valentin Schneider <valentin.schneider@arm.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Thara Gopinath <thara.gopinath@linaro.org>,
Viresh Kumar <viresh.kumar@linaro.org>,
Todd Kjos <tkjos@google.com>,
Joel Fernandes <joel@joelfernandes.org>,
Steve Muckle <smuckle@google.com>,
adharmap@codeaurora.org, Saravana Kannan <skannan@codeaurora.org>,
Pavan Kondeti <pkondeti@codeaurora.org>,
Juri Lelli <juri.lelli@redhat.com>,
Eduardo Valentin <edubezval@gmail.com>,
Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
currojerez@riseup.net, Javi Merino <javi.merino@kernel.org>
Subject: Re: [PATCH v6 13/14] sched/topology: Make Energy Aware Scheduling depend on schedutil
Date: Mon, 10 Sep 2018 10:43:01 +0100 [thread overview]
Message-ID: <20180910094255.nzjjsiphjplh7ruk@queper01-lin> (raw)
In-Reply-To: <CAJZ5v0jSE2u7DpT6KBiR=zEN0RSBq4cO1Ve=e+pju6cwj8toFQ@mail.gmail.com>
On Monday 10 Sep 2018 at 10:55:43 (+0200), Rafael J. Wysocki wrote:
> On Mon, Sep 10, 2018 at 10:24 AM Quentin Perret <quentin.perret@arm.com> wrote:
> >
> > Hi Rafael,
> >
> > On Sunday 09 Sep 2018 at 22:13:52 (+0200), Rafael J. Wysocki wrote:
> > > On Fri, Sep 7, 2018 at 5:29 PM Quentin Perret <quentin.perret@arm.com> wrote:
> > > > On Friday 07 Sep 2018 at 10:52:01 (+0200), Rafael J. Wysocki wrote:
> > > > > Well, why don't you implement it as something like "if the governor changes
> > > > > from sugov to something else (or the other way around), call this function
> > > > > from the scheduler"?
> > > >
> > > > I just gave it a try and ended up with the diff below. It's basically
> > > > the exact same patch with a direct function call instead of a notifier.
> > > > (I also tried the sugov_start/stop thing I keep mentioning but it is
> > > > more complex, so let's see if the simplest solution could work first).
> > > >
> > > > What do you think ?
> > >
> > > This generally works for me from the cpufreq perspective, but I would
> > > add "cpufreq" to the name of the new function, that is call it
> > > something like sched_cpufreq_governor_change().
> >
> > Ok, no problem.
> >
> > > Also do you really need the extra work item? Governor changes are
> > > carried out in process context anyway.
> >
> > Ah, good point, I can remove that. I just tried and got the following
> > lock warning on boot, though:
> >
> > [ 2.518684] ============================================
> > [ 2.523942] WARNING: possible recursive locking detected
> > [ 2.529200] 4.18.0-rc6-00086-g940e7a9fd5ec #10 Not tainted
> > [ 2.534630] --------------------------------------------
> > [ 2.539888] kworker/2:3/1349 is trying to acquire lock:
> > [ 2.545059] (____ptrval____) (cpu_hotplug_lock.rw_sem){++++}, at: rebuild_sched_domains_locked+0x2c/0x598
> > [ 2.554559]
> > [ 2.554559] but task is already holding lock:
> > [ 2.560332] (____ptrval____) (cpu_hotplug_lock.rw_sem){++++}, at: cpufreq_register_driver+0x80/0x1d0
> > [ 2.569396]
> > [ 2.569396] other info that might help us debug this:
> > [ 2.575858] Possible unsafe locking scenario:
> > [ 2.575858]
> > [ 2.581717] CPU0
> > [ 2.584135] ----
> > [ 2.586553] lock(cpu_hotplug_lock.rw_sem);
> > [ 2.590785] lock(cpu_hotplug_lock.rw_sem);
> > [ 2.595017]
> > [ 2.595017] *** DEADLOCK ***
> > [ 2.595017]
> > [ 2.600877] May be due to missing lock nesting notation
> >
> > That seems to happen because cpufreq_register_driver() calls
> > cpus_read_lock(), which is then called again by rebuild_sched_domains()
> > down the line. So it might just be a missing lock nesting notation as
> > the warning suggests ?
> >
> > I'll have a look.
>
> It only is nested in the _register_driver() code path, otherwise it may not be.
Right.
> Using the work item may be the most straightforward way to deal with
> that, but then I would add a comment to explain what's up.
Indeed, rw_sems don't seem to be appropriate for nested locking:
https://elixir.bootlin.com/linux/latest/source/include/linux/rwsem.h#L156
I'll stick a comment explaining that for now, unless I find a better
idea than using a work item in the meantime.
Thanks,
Quentin
next prev parent reply other threads:[~2018-09-10 9:43 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-20 9:44 [PATCH v6 00/14] Energy Aware Scheduling Quentin Perret
2018-08-20 9:44 ` [PATCH v6 01/14] sched: Relocate arch_scale_cpu_capacity Quentin Perret
2018-08-20 9:44 ` [PATCH v6 02/14] sched/cpufreq: Factor out utilization to frequency mapping Quentin Perret
2018-09-10 9:29 ` Rafael J. Wysocki
2018-08-20 9:44 ` [PATCH v6 03/14] PM: Introduce an Energy Model management framework Quentin Perret
2018-08-29 10:04 ` Patrick Bellasi
2018-08-29 13:28 ` Quentin Perret
2018-08-31 9:04 ` Patrick Bellasi
2018-09-11 9:34 ` Andrea Parri
2018-09-11 12:32 ` Quentin Perret
2018-09-11 13:31 ` Andrea Parri
2018-09-10 9:44 ` Rafael J. Wysocki
2018-09-10 10:38 ` Quentin Perret
2018-09-10 10:40 ` Rafael J. Wysocki
2018-08-20 9:44 ` [PATCH v6 04/14] PM / EM: Expose the Energy Model in sysfs Quentin Perret
2018-09-06 6:56 ` Dietmar Eggemann
2018-09-06 14:09 ` Quentin Perret
2018-09-07 0:14 ` Dietmar Eggemann
2018-08-20 9:44 ` [PATCH v6 05/14] sched/topology: Reference the Energy Model of CPUs when available Quentin Perret
2018-08-29 16:22 ` Patrick Bellasi
2018-08-29 16:56 ` Quentin Perret
2018-08-30 10:00 ` Patrick Bellasi
2018-08-30 10:47 ` Quentin Perret
2018-08-30 12:50 ` Patrick Bellasi
2018-08-20 9:44 ` [PATCH v6 06/14] sched/topology: Lowest CPU asymmetry sched_domain level pointer Quentin Perret
2018-08-20 9:44 ` [PATCH v6 07/14] sched/topology: Introduce sched_energy_present static key Quentin Perret
2018-08-29 16:50 ` Patrick Bellasi
2018-08-29 17:20 ` Quentin Perret
2018-08-30 9:23 ` Patrick Bellasi
2018-08-30 9:57 ` Quentin Perret
2018-08-30 10:18 ` Patrick Bellasi
2018-09-06 6:06 ` Dietmar Eggemann
2018-09-06 9:29 ` Quentin Perret
2018-09-06 23:49 ` Dietmar Eggemann
2018-09-07 8:24 ` Quentin Perret
2018-08-20 9:44 ` [PATCH v6 08/14] sched/fair: Clean-up update_sg_lb_stats parameters Quentin Perret
2018-08-20 9:44 ` [PATCH v6 09/14] sched: Add over-utilization/tipping point indicator Quentin Perret
2018-08-20 9:44 ` [PATCH v6 10/14] sched/cpufreq: Refactor the utilization aggregation method Quentin Perret
2018-09-10 9:53 ` Rafael J. Wysocki
2018-09-10 10:07 ` Quentin Perret
2018-09-10 10:25 ` Rafael J. Wysocki
2018-08-20 9:44 ` [PATCH v6 11/14] sched/fair: Introduce an energy estimation helper function Quentin Perret
2018-08-20 9:44 ` [PATCH v6 12/14] sched/fair: Select an energy-efficient CPU on task wake-up Quentin Perret
2018-08-20 9:44 ` [PATCH v6 13/14] sched/topology: Make Energy Aware Scheduling depend on schedutil Quentin Perret
2018-09-04 10:59 ` Quentin Perret
2018-09-06 9:18 ` Rafael J. Wysocki
2018-09-06 14:38 ` Quentin Perret
2018-09-07 8:52 ` Rafael J. Wysocki
2018-09-07 8:56 ` Rafael J. Wysocki
2018-09-07 9:02 ` Quentin Perret
2018-09-07 15:29 ` Quentin Perret
2018-09-09 20:13 ` Rafael J. Wysocki
2018-09-10 8:24 ` Quentin Perret
2018-09-10 8:55 ` Rafael J. Wysocki
2018-09-10 9:43 ` Quentin Perret [this message]
2018-08-20 9:44 ` [PATCH v6 14/14] OPTIONAL: cpufreq: dt: Register an Energy Model Quentin Perret
2018-09-10 9:12 ` [PATCH v6 00/14] Energy Aware Scheduling Rafael J. Wysocki
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