On 30-03-17, 23:36, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki <[email protected]> > > The schedutil governor reduces frequencies too fast in some > situations which cases undesirable performance drops to > appear. > > To address that issue, make schedutil reduce the frequency slower by > setting it to the average of the value chosen during the previous > iteration of governor computations and the new one coming from its > frequency selection formula. > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=194963 > Reported-by: John <[email protected]> > Signed-off-by: Rafael J. Wysocki <[email protected]> > --- > > This addresses a practical issue, but one in the "responsiveness" or > "interactivity" category which is quite hard to represent quantitatively. > > As reported by John in BZ194963, schedutil does not ramp up P-states quickly > enough which causes audio issues to appear in his gaming setup. At least it > evidently is worse than ondemand in this respect and the patch below helps. > > The patch essentially repeats the trick added some time ago to the load-based > P-state selection algorithm in intel_pstate, which allowed us to make it > viable > for performance-oriented users, and which is to reduce frequencies at a slower > pace. > > The reason why I chose the average is because it is computationally cheap > and pretty much the max reasonable slowdown and the idea is that in case > there's something about to run that we don't know about yet, it is better to > stay at a higher level for a while more to avoid having to get up from the > floor > every time. > > But technically speaking it is a filter. :-) > > So among other things I'm wondering if that leads to substantial increases in > energy consumption anywhere. > > Thanks, > Rafael > > --- > kernel/sched/cpufreq_schedutil.c | 3 +++ > 1 file changed, 3 insertions(+) > > Index: linux-pm/kernel/sched/cpufreq_schedutil.c > =================================================================== > --- linux-pm.orig/kernel/sched/cpufreq_schedutil.c > +++ linux-pm/kernel/sched/cpufreq_schedutil.c > @@ -101,6 +101,9 @@ static void sugov_update_commit(struct s > if (sg_policy->next_freq == next_freq) > return; >
Maybe add a comment over here on why we are adding this workaround . > + if (sg_policy->next_freq > next_freq) > + next_freq = (sg_policy->next_freq + next_freq) >> 1; > + > sg_policy->next_freq = next_freq; > sg_policy->last_freq_update_time = time; Acked-by: Viresh Kumar <[email protected]> -- viresh
