Re: [PATCH] aio: make aio wait path to account iowait time

[peterz]

On Fri, Aug 28, 2020 at 02:07:12PM +0800, Xianting Tian wrote:
> As the normal aio wait path(read_events() ->
> wait_event_interruptible_hrtimeout()) doesn't account iowait time, so use
> this patch to make it to account iowait time, which can truely reflect
> the system io situation when using a tool like 'top'.

Do be aware though that io_schedule() is potentially far more expensive
than regular schedule() and io-wait accounting as a whole is a
trainwreck.

When in_iowait is set schedule() and ttwu() will have to do additional
atomic ops, and (much) worse, PSI will take additional locks.

And all that for a number that, IMO, is mostly useless, see the comment
with nr_iowait().

But, if you don't care about performance, and want to see a shiny random
number generator, by all means, use io_schedule().