On Tue, Oct 27, 2020 at 5:26 AM Viresh Kumar <viresh.ku...@linaro.org> wrote:
>
> Spelling mistake in $subject (driver)
>
> On 23-10-20, 17:36, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wyso...@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 clear
> > need_freq_update only if the CPUFREQ_NEED_UPDATE_LIMITS flag is
> > not set for the cpufreq driver in use (and it should be set for all
> > potentially affected drivers) and make sugov_update_next_freq()
> > check need_freq_update and continue when it is set regardless of
> > whether or not the new target frequency is equal to the old one.
> >
> > Fixes: f6ebbcf08f37 ("cpufreq: intel_pstate: Implement passive mode with
> > HWP enabled")
> > Reported-by: Zhang Rui <rui.zh...@intel.com>
> > Cc: 5.9+ <sta...@vger.kernel.org> # 5.9+
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wyso...@intel.com>
> > ---
> >
> > New patch in v2.
> >
> > ---
> > kernel/sched/cpufreq_schedutil.c | 8 ++++++--
> > 1 file changed, 6 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
> > @@ -102,11 +102,12 @@ 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 && !sg_policy->need_freq_update)
> > return false;
> >
> > sg_policy->next_freq = next_freq;
> > sg_policy->last_freq_update_time = time;
> > + sg_policy->need_freq_update = false;
> >
> > return true;
> > }
> > @@ -164,7 +165,10 @@ static unsigned int get_next_freq(struct
> > if (freq == sg_policy->cached_raw_freq &&
> > !sg_policy->need_freq_update)
> > return sg_policy->next_freq;
> >
> > - sg_policy->need_freq_update = false;
> > + if (sg_policy->need_freq_update)
> > + sg_policy->need_freq_update =
> > + cpufreq_driver_test_flags(CPUFREQ_NEED_UPDATE_LIMITS);
> > +
>
> The behavior here is a bit different from what we did in cpufreq.c. In cpufreq
> core we are _always_ allowing the call to reach the driver's target() routine,
> but here we do it only if limits have changed. Wonder if we should have
> similar
> behavior here as well ?
I didn't think about that, but now that you mentioned it, I think that
this is a good idea.
Will send an updated patch with that implemented shortly.
> Over that the code here can be rewritten a bit like:
>
> if (sg_policy->need_freq_update)
> sg_policy->need_freq_update =
> cpufreq_driver_test_flags(CPUFREQ_NEED_UPDATE_LIMITS);
> else if (freq == sg_policy->cached_raw_freq)
> return sg_policy->next_freq;
Right, but it will be somewhat different anyway. :-)
