On Tue, Jul 11, 2017 at 7:14 AM, Joel Fernandes <joe...@google.com> wrote:
[..]
>>> + }
>>> } else if (sg_cpu->iowait_boost) {
>>> s64 delta_ns = time - sg_cpu->last_update;
>>>
>>> /* Clear iowait_boost if the CPU apprears to have been idle.
>>> */
>>> if (delta_ns > TICK_NSEC)
>>> sg_cpu->iowait_boost = 0;
>>> +
>>> + /*
>>> + * Since we don't decay iowait_boost when its consumed during
>>> + * the previous SCHED_CPUFREQ_IOWAIT update, decay it now.
>>> + */
>>> + if (sg_cpu->prev_iowait_boost) {
>>
>> SCHED_CPUFREQ_IOWAIT flag is set only by CFS from the enqueue_task() and in
>> many
>> cases we call the util hook twice from the same enqueue_task() instance
>> before
>> returning (2nd one after updating util). And in such cases we will set
>> iowait_boost as 0 on the second call.
>>
>> Have you ever seen two consecutive calls to sugov_set_iowait_boost() with
>> IOWAIT
>> flag set ? Can we get the ratio of that against the other case where we have
>> IOWAIT flag set in first call, followed by one or more non-IOWAIT calls and
>> then
>> IOWAIT again ?
>>
>> I am asking because if the calls with IOWAIT flag aren't consecutive then we
>> will make iowait_boost as 0 in the next non-IOWAIT call.
>
> Yes, I've seen that happen in my testing (consecutive iowait). I
> haven't seen the other case where you have IOWAIT followed by
> non-IOWAIT for a repeated set of IOWAIT requests. Would you more
> comfortable if we moved sugov_set_iowait_boost() after the
> sugov_should_update_freq() ? That way if there are consecutive
> requests in the same path, then it most likely rate-limiting will
> prevent such updates. I will also try to collect some stats as you
> suggested to see if how often if at all this can happen.
Just to be more clear, I was saying that I've only seen repeated
IOWAIT requests in the update path, not IOWAIT followed by non-IOWAIT
cpufreq updates for a repeated sequence of IOWAIT wakeups.
thanks,
-Joel
