Re: [PATCH v1] sched/cputime: Preserve iowait accounting across waking interrupts in dyntick-idle

[Peter Zijlstra]

On Wed, Oct 14, 2026 at 02:17:52PM +0100, Christian Loehle wrote:

> > Using nr_iowait_cpu() is fundamentally never a fix. It is rolling a dice
> > and liking random numbers. See the comment that goes with that function.
> > 
> Speaking of, that comment is stale, menu doesn't use that heuristic anymore.

\o/

> FWIW the remaining aggregated nr_iowait users seem to be accounting/reporting.
> (cpufreq still uses it, but it comes directly from p->in_iowait).

I see: get_cpu_iowait_time_us() using nr_cpuwait_cpu(), which in turn is
used for both thermal and cpufreq.

> Given they are exported (/proc/stat procs_blocked and something in s390) I don't
> see how we can remove this entirely but at least nr_iowait_cpu() as opposed
> to cpu_has_iowait() could be refactored. The issues are obviously the same still.
> I'll send a patch.

Right.

> Peter, if you see a path to ever retire iowait (or at least the CPU iowait for now),
> I'm more than happy to sink some time into it...

Given the exposure in /proc I'm not sure we can *ever* fully get rid of
the per-cpu usage of iowait, but yeah, reducing in-kernel consumers of
this number might be somewhat feasible.