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.per...@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.
Thanks,
Quentin
