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    SubjectRe: [PATCH 1/4] nohz: Only update sleeptime stats locally
    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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