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SubjectRe: [PATCH] [RFC] cpufreq: can't raise max frequency with cpu_thermal
On Wed, Dec 26, 2012 at 11:32 AM, amit daniel kachhap
<amit.daniel@samsung.com> wrote:
>
> On Tue, Dec 18, 2012 at 9:45 PM, Doug Anderson <dianders@chromium.org> wrote:
> > Amit,
> >
> > On Tue, Dec 18, 2012 at 8:17 PM, amit daniel kachhap
> > <amit.daniel@samsung.com> wrote:
> >> On Tue, Dec 18, 2012 at 12:29 AM, Sonny Rao <sonnyrao@chromium.org> wrote:
> >>> The cpu_thermal generic thermal management code has a bug where once
> >>> max cpu frequency has been lowered in sysfs (scaling_max_freq) it is
> >>> not possible to raise the max back up later. The bug is that the
> >>> notifer gets called by __cpufreq_set_policy() before the user policy
> >>> max is raised, and is incorrectly trying to enforce the max frequency
> >>> policy even when we are trying to change the policy. It is also not
> >>> clear why this driver is looking at the user policy since it is
> >>> primarily supposed to enforce thermal policy, not user set policy.
> >>
> >> Hi Sunny,
> >>
> >> I am not sure if this change is needed.
> >
> > Do you have a machine that's running with your code? Can you go into
> > sysfs (/sys/devices/system/cpu/cpu0/cpufreq/) and try lowering then
> > raising the max frequency by doing something like this (assumes that
> > you can scale down to 200MHz):
> >
> > cd /sys/devices/system/cpu/cpu0/cpufreq/
> > OLD_VAL=$(cat scaling_max_freq)
> > cat scaling_min_freq > scaling_max_freq
> > echo ${OLD_VAL} > scaling_max_freq
> >
> > echo "$(cat scaling_max_freq) should be ${OLD_VAL}. Is it?"
> >
> > ...when I run the above without Sonny's patch on my system I see:
> > 200000 should be 1700000. Is it?
> >
> > ...after Sonny's patch then the above works.
> Hi Doug,
>
> I tested the above steps on exynos origen board with all cpufreq
> cooling configs enabled in kernel version 3.8-rc1.
> In my tests I am able to vary scaling_max_freq to all values. Also I
> am in normal temperature threshold. So basically I am not able to
> reproduce the error reported,
>
> Thanks,
> Amit Daniel


Hi, thanks for checking it out. I'm a bit surprised that you couldn't
reproduce it, but it might just be that it will only manifest on a
platform which is using that driver - like Exynos 5? We'll try it out
on a 3.8-rc on an Exynos and let you know if we see it or not.

Thanks again,
Sonny


>
> >
> >> There is a check in cpufreq_thermal_notifier function to return 0 if
> >> notify_device == NOTIFY_INVALID. So the user will be always able to
> >> change the max frequency in normal situation. Did you tested this for
> >> some corner cases?
> >> The reason behind putting this check is that I don't want to override
> >> the user constraints.
> >>
> >> Thanks,
> >> Amit Daniel
> >>
> >>>
> >>> Signed-off-by: Sonny Rao <sonnyrao@chromium.org>
> >>> ---
> >>> drivers/thermal/cpu_cooling.c | 4 ----
> >>> 1 files changed, 0 insertions(+), 4 deletions(-)
> >>>
> >>> diff --git a/drivers/thermal/cpu_cooling.c b/drivers/thermal/cpu_cooling.c
> >>> index 836828e..63bc708 100644
> >>> --- a/drivers/thermal/cpu_cooling.c
> >>> +++ b/drivers/thermal/cpu_cooling.c
> >>> @@ -219,10 +219,6 @@ static int cpufreq_thermal_notifier(struct notifier_block *nb,
> >>> if (cpumask_test_cpu(policy->cpu, &notify_device->allowed_cpus))
> >>> max_freq = notify_device->cpufreq_val;
> >>>
> >>> - /* Never exceed user_policy.max*/
> >>> - if (max_freq > policy->user_policy.max)
> >>> - max_freq = policy->user_policy.max;
> >>> -
> >>> if (policy->max != max_freq)
> >>> cpufreq_verify_within_limits(policy, 0, max_freq);
> >>>
> >>> --
> >>> 1.7.7.3
> >>>
> >>> --
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> >
> > -Doug
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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