On Tue, Sep 09, 2014 at 11:56:18AM +0530, Viresh Kumar wrote: > On Tue, Sep 9, 2014 at 11:02 AM, Anup Chenthamarakshan > <an...@chromium.org> wrote: > > I had initially tried reusing cpufreq_stats.c to export stats. > > Calling cpufreq_stats_update() via the cpufreq notifier added > > some amount of overhead while switching frequencies. Specifically, > > looking up the index of the new frequency in freq_table_get_index() > > is a linear search through all available frequencies (vs a single > > subtraction with custom stats export). Also, the notifier mechanism > > I don't think just this linear search will make things so bad..
Linear search usually slows down transition to higher P-states because it has to go through the full list (and the list is longer in intel_pstate compared to acpi-cpufreq). But, yes, this is probably not a bottleneck. > > > itself added a level of indirection before calling stats_update. > > Probably some other notifier is registered which is taking considerable > amount of time.. Try checking what all registered with cpufreq-core. There was no other notifier which was listening to freq transitions events. > > > There is a 5X increase in time taken to complete intel_pstate_set_pstate > > while using cpufreq_stats compared to having custom stats exported. > > Try calling cpufreq_stat_notifier_trans() directly instead of a notifier > and lets see if this makes it any better. Here's a comparison of time taken to run intel_pstate_set_pstate() using different approaches: average time for a transition no stats 4.7us intel_pstate-stats 5.7us direct call to cpufreq_stat_notifier_trans 8.1us cpufreq-notifier-event 10.6us I was wrong about the 5x increase (got tripped by calls to intel_pstate_set_pstate where no change in P-state actually happened) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/