Messages in this thread | | | Date | Sun, 18 Aug 2013 23:38:58 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 1/4] nohz: Only update sleeptime stats locally |
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On Sun, Aug 18, 2013 at 06:49:37PM +0200, Oleg Nesterov wrote: > On 08/16, Frederic Weisbecker wrote: > > > > To fix this, lets only update the sleeptime stats locally when the CPU > > exits from idle. > > I am in no position to ack the changes in this area, but I like this > change very much. Because, as a code reader, I was totally confused by > > if (last_update_time) > update_ts_time_stats() > > code and it looks "obviously wrong". > > I added more cc's. It seems to me that 9366d840 "cpufreq: governors: > Calculate iowait time only when necessary" doesn't realize what > > - u64 idle_time = get_cpu_idle_time_us(cpu, NULL); > + u64 idle_time = get_cpu_idle_time_us(cpu, io_busy ? wall : NULL); > > actually means. OTOH, get_cpu_iowait_time_us() was called with > last_update_time != NULL even before this patch... > > In short. This looks like the clear fix to me, but I do not understand > this code enough, and I think that cpufreq should know about this change.
Good point, and this time I'm really adding the Cc :)
> > > static void tick_nohz_stop_idle(int cpu, ktime_t now) > > { > > struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); > > + ktime_t delta; > > > > - update_ts_time_stats(cpu, ts, now, NULL); > > + /* Updates the per cpu time idle statistics counters */ > > + delta = ktime_sub(now, ts->idle_entrytime); > > + if (nr_iowait_cpu(cpu) > 0) > > + ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta); > > + else > > + ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta); > > + ts->idle_entrytime = now; > > ts->idle_active = 0; > > With or without this change, why we update ->idle_entrytime in this case? > Looks harmless, but a bit confusing.
Oh indeed I missed that. It's a leftover from the copy-paste of update_ts_time_stats() content.
Well spotted, I'll fix.
> > While this doesn't really matter, we could probably even kill ->idle_active > and use !!ts->idle_entrytime instead.
We could but it would be slightly more overhead in the irq entry path (cf: tick_check_nohz()) and it makes the code also a little bit harder to review IMHO.
> > > @@ -473,17 +458,14 @@ u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time) > > And I think that we should kill this last_update_time argument later.
Agreed.
Thanks.
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