Messages in this thread Patch in this message | | | Date | Sun, 18 Aug 2013 19:04:08 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH 1/4] nohz: Only update sleeptime stats locally |
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Sorry for double post. forgot to cc cpufreq maintainers.
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.
> 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.
While this doesn't really matter, we could probably even kill ->idle_active and use !!ts->idle_entrytime instead.
> @@ -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.
Oleg.
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