Re: [PATCH v3 0/4] sched,time: fix irq time accounting with nohz_idle

Nikolay Borisov
2016-07-05T13:03:50Z

On 06/30/2016 10:35 PM, riel@redhat.com wrote:
> Currently irq time accounting only works in these cases:
> 1) purely ticke based accounting
> 2) nohz_full accounting, but only on housekeeping & nohz_full CPUs
> 3) architectures with native vtime accounting
>
> On nohz_idle CPUs, which are probably the majority nowadays,
> irq time accounting is currently broken. This leads to systems
> reporting a dramatically lower amount of irq & softirq time than
> is actually spent handling them, with all the time spent while the
> system is in the idle task being accounted as idle.

Is this supposed to alleviate the issue reported here:
http://www.gossamer-threads.com/lists/linux/kernel/2169180

>
> This patch set seems to bring the amount of irq time reported by
> top (and /proc/stat) roughly in line with that measured when I do
> a "perf record -g -a" run to see what is using all that time.
>
> The amount of irq time used, especially softirq, is shockingly high,
> to the point of me thinking this patch set may be wrong, but the
> numbers seem to match what perf is giving me...
>
> These patches apply on top of Wanpeng Li's steal time patches.
>
> CONFIG_IRQ_TIME_ACCOUNTING is now a config option that is available
> as a separate choice from tick based / nohz_idle / nohz_full mode,
> a suggested by Frederic Weisbecker.
>
> Next up: look at the things that are using CPU time on an otherwise
> idle system, and see if I can make those a little faster :)
>
> v2: address Peterz's concerns, some more cleanups
> v3: rewrite the code along Frederic's suggestions, now cputime_t
> is used everywhere
>