On Fri, May 18, 2018 at 11:13 PM, Saravana Kannan <[email protected]> wrote: > On 05/18/2018 11:55 AM, Joel Fernandes (Google.) wrote: >> >> From: "Joel Fernandes (Google)" <[email protected]> >> >> Currently there is a chance of a schedutil cpufreq update request to be >> dropped if there is a pending update request. This pending request can >> be delayed if there is a scheduling delay of the irq_work and the wake >> up of the schedutil governor kthread. >> >> A very bad scenario is when a schedutil request was already just made, >> such as to reduce the CPU frequency, then a newer request to increase >> CPU frequency (even sched deadline urgent frequency increase requests) >> can be dropped, even though the rate limits suggest that its Ok to >> process a request. This is because of the way the work_in_progress flag >> is used. >> >> This patch improves the situation by allowing new requests to happen >> even though the old one is still being processed. Note that in this >> approach, if an irq_work was already issued, we just update next_freq >> and don't bother to queue another request so there's no extra work being >> done to make this happen. >> >> I had brought up this issue at the OSPM conference and Claudio had a >> discussion RFC with an alternate approach [1]. I prefer the approach as >> done in the patch below since it doesn't need any new flags and doesn't >> cause any other extra overhead. >> >> [1] https://patchwork.kernel.org/patch/10384261/ >> >> LGTMed-by: Viresh Kumar <[email protected]> >> LGTMed-by: Juri Lelli <[email protected]> >> CC: Viresh Kumar <[email protected]> >> CC: Rafael J. Wysocki <[email protected]> >> CC: Peter Zijlstra <[email protected]> >> CC: Ingo Molnar <[email protected]> >> CC: Patrick Bellasi <[email protected]> >> CC: Juri Lelli <[email protected]> >> Cc: Luca Abeni <[email protected]> >> CC: Joel Fernandes <[email protected]> >> CC: Todd Kjos <[email protected]> >> CC: [email protected] >> CC: [email protected] >> CC: [email protected] >> Signed-off-by: Joel Fernandes (Google) <[email protected]> >> --- >> v1 -> v2: Minor style related changes. >> >> kernel/sched/cpufreq_schedutil.c | 34 ++++++++++++++++++++++++-------- >> 1 file changed, 26 insertions(+), 8 deletions(-) >> >> diff --git a/kernel/sched/cpufreq_schedutil.c >> b/kernel/sched/cpufreq_schedutil.c >> index e13df951aca7..5c482ec38610 100644 >> --- a/kernel/sched/cpufreq_schedutil.c >> +++ b/kernel/sched/cpufreq_schedutil.c >> @@ -92,9 +92,6 @@ static bool sugov_should_update_freq(struct sugov_policy >> *sg_policy, u64 time) >> !cpufreq_can_do_remote_dvfs(sg_policy->policy)) >> return false; >> >> - if (sg_policy->work_in_progress) >> - return false; >> - >> if (unlikely(sg_policy->need_freq_update)) { >> sg_policy->need_freq_update = false; >> /* >> @@ -128,7 +125,7 @@ static void sugov_update_commit(struct sugov_policy >> *sg_policy, u64 time, >> >> policy->cur = next_freq; >> trace_cpu_frequency(next_freq, smp_processor_id()); >> - } else { >> + } else if (!sg_policy->work_in_progress) { > > > Not really something you added, but if you are modifying it: > Do we really need this work_in_progress flag? irq_work_queue() already > checks if the work is pending and then returns true/false. > > Wouldn't the issue you are trying to fix be resolved just by dropping this > flag check entirely?
You've missed the entire discussion on that several days ago, sorry. Thanks, Rafael
