lkml.org 
[lkml]   [2020]   [Oct]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v2.2 4/4] cpufreq: schedutil: Always call driver if CPUFREQ_NEED_UPDATE_LIMITS is set
On Thu, Oct 29, 2020 at 12:23 PM Viresh Kumar <viresh.kumar@linaro.org> wrote:
>
> On 29-10-20, 12:12, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >
> > Because sugov_update_next_freq() may skip a frequency update even if
> > the need_freq_update flag has been set for the policy at hand, policy
> > limits updates may not take effect as expected.
> >
> > For example, if the intel_pstate driver operates in the passive mode
> > with HWP enabled, it needs to update the HWP min and max limits when
> > the policy min and max limits change, respectively, but that may not
> > happen if the target frequency does not change along with the limit
> > at hand. In particular, if the policy min is changed first, causing
> > the target frequency to be adjusted to it, and the policy max limit
> > is changed later to the same value, the HWP max limit will not be
> > updated to follow it as expected, because the target frequency is
> > still equal to the policy min limit and it will not change until
> > that limit is updated.
> >
> > To address this issue, modify get_next_freq() to let the driver
> > callback run if the CPUFREQ_NEED_UPDATE_LIMITS cpufreq driver flag
> > is set regardless of whether or not the new frequency to set is
> > equal to the previous one.
> >
> > Fixes: f6ebbcf08f37 ("cpufreq: intel_pstate: Implement passive mode with HWP enabled")
> > Reported-by: Zhang Rui <rui.zhang@intel.com>
> > Tested-by: Zhang Rui <rui.zhang@intel.com>
> > Cc: 5.9+ <stable@vger.kernel.org> # 5.9+
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > ---
> >
> > v2.1 -> v2.2:
> > * Instead of updating need_freq_update if CPUFREQ_NEED_UPDATE_LIMITS is set
> > in get_next_freq() and checking it again in sugov_update_next_freq(),
> > check CPUFREQ_NEED_UPDATE_LIMITS directly in sugov_update_next_freq().
> > * Update the subject.
> >
> > v2 -> v2.1:
> > * Fix typo in the subject.
> > * Make get_next_freq() and sugov_update_next_freq() ignore the
> > sg_policy->next_freq == next_freq case when CPUFREQ_NEED_UPDATE_LIMITS
> > is set for the driver.
> > * Add Tested-by from Rui (this version lets the driver callback run more
> > often than the v2, so the behavior in the Rui's case doesn't change).
> >
> > ---
> > kernel/sched/cpufreq_schedutil.c | 6 ++++--
> > 1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > Index: linux-pm/kernel/sched/cpufreq_schedutil.c
> > ===================================================================
> > --- linux-pm.orig/kernel/sched/cpufreq_schedutil.c
> > +++ linux-pm/kernel/sched/cpufreq_schedutil.c
> > @@ -102,7 +102,8 @@ static bool sugov_should_update_freq(str
> > static bool sugov_update_next_freq(struct sugov_policy *sg_policy, u64 time,
> > unsigned int next_freq)
> > {
> > - if (sg_policy->next_freq == next_freq)
> > + if (sg_policy->next_freq == next_freq &&
> > + !cpufreq_driver_test_flags(CPUFREQ_NEED_UPDATE_LIMITS))
> > return false;
>
> Since sg_policy->next_freq is used elsewhere as well, this is the best
> we can do here.
>
> > sg_policy->next_freq = next_freq;
> > @@ -161,7 +162,8 @@ static unsigned int get_next_freq(struct
> >
> > freq = map_util_freq(util, freq, max);
> >
> > - if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update)
> > + if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update &&
> > + !cpufreq_driver_test_flags(CPUFREQ_NEED_UPDATE_LIMITS))
> > return sg_policy->next_freq;
> >
> > sg_policy->need_freq_update = false;
>
> But I was wondering if instead of this we just do this here:
>
> if (!cpufreq_driver_test_flags(CPUFREQ_NEED_UPDATE_LIMITS))
> sg_policy->cached_raw_freq = freq;
>
> And so the above check will always fail.

I wrote it this way, because I want to avoid looking at the driver
flags at all unless the update is going to be skipped. Otherwise we
may end up fetching a new cache line here every time even if that is
not needed.

> Acked-by: Viresh Kumar <viresh.kumar@linaro.org>

Thanks!

\
 
 \ /
  Last update: 2020-10-29 12:30    [W:0.077 / U:0.660 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site