On Thu, Oct 29, 2020 at 12:23 PM Viresh Kumar <[email protected]> wrote: > > On 29-10-20, 12:12, Rafael J. Wysocki wrote: > > From: Rafael J. Wysocki <[email protected]> > > > > 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 <[email protected]> > > Tested-by: Zhang Rui <[email protected]> > > Cc: 5.9+ <[email protected]> # 5.9+ > > Signed-off-by: Rafael J. Wysocki <[email protected]> > > --- > > > > 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 <[email protected]> Thanks!
