On 08/18/2013 08:04 PM, Oleg Nesterov wrote:
> 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...
To be honest, I am unfamiliar with tick-sched code.
With patch 9366d840, I was trying to avoid duplicate calls to
get_cpu_iowait_time_us function. I just saw that the original
code was calling update_ts_time_stats within get_cpu_idle_time_us
and get_cpu_iowait_time_us and I thought that I should keep calling
these functions with non NULL parameter to update the time stats.
In fact the original patch submission was without this:
- u64 idle_time = get_cpu_idle_time_us(cpu, NULL);
+ u64 idle_time = get_cpu_idle_time_us(cpu, io_busy ? wall : NULL);
and the idle time calculation was wrong (ondemand couldn't increase to max freq)
For your convenience the call paths before and after this patch:
Before patch
get_cpu_idle_time(j, &cur_wall_time);
u64 idle_time = get_cpu_idle_time_us(cpu, NULL);
idle_time += get_cpu_iowait_time_us(cpu, wall);
update_ts_time_stats(cpu, ts, now, last_update_time);
...
get_cpu_iowait_time_us(j, &cur_wall_time);
update_ts_time_stats(cpu, ts, now, last_update_time);
After patch (io_busy = 1)
cur_idle_time = get_cpu_idle_time(j, &cur_wall_time, io_busy);
u64 idle_time = get_cpu_idle_time_us(cpu, io_busy ? wall : NULL);
update_ts_time_stats(cpu, ts, now, last_update_time);
After patch (io_busy = 0)
cur_idle_time = get_cpu_idle_time(j, &cur_wall_time, io_busy);
u64 idle_time = get_cpu_idle_time_us(cpu, io_busy ? wall : NULL);
idle_time += get_cpu_iowait_time_us(cpu, wall);
update_ts_time_stats(cpu, ts, now, last_update_time);
Regards,
Stratos
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
