On Wed 05-08-20 09:35:51, Xianting Tian wrote:
> When waiting for the completion of io, we need account iowait time. As
> wait_for_completion() calls schedule_timeout(), which doesn't account
> iowait time. While wait_for_completion_io() calls io_schedule_timeout(),
> which will account iowait time.
>
> So using wait_for_completion_io() instead of wait_for_completion()
> when waiting for completion of io before exit_aio and io_destroy.
>
> Signed-off-by: Xianting Tian <xianting_tian@xxxxxxx>
Thanks for the patch! It looks good to me but IMO this is just scratching
the surface. E.g. for AIO we are mostly going to wait in read_events() by
wait_event_interruptible_hrtimeout() and *that* doesn't account as IO wait
either? Which is IMO far bigger misaccounting... The two case you fix seem
to be just rare cornercases so what they do isn't a big deal either way.
So I agree it may be worth it to properly account waiting for AIO but if
you want to do that, then please handle mainly the common cases in AIO
code.
Honza
> ---
> fs/aio.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/aio.c b/fs/aio.c
> index 91e7cc4..498b8a0 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -892,7 +892,7 @@ void exit_aio(struct mm_struct *mm)
>
> if (!atomic_sub_and_test(skipped, &wait.count)) {
> /* Wait until all IO for the context are done. */
> - wait_for_completion(&wait.comp);
> + wait_for_completion_io(&wait.comp);
> }
>
> RCU_INIT_POINTER(mm->ioctx_table, NULL);
> @@ -1400,7 +1400,7 @@ static long read_events(struct kioctx *ctx, long min_nr, long nr,
> * is destroyed.
> */
> if (!ret)
> - wait_for_completion(&wait.comp);
> + wait_for_completion_io(&wait.comp);
>
> return ret;
> }
> --
> 1.8.3.1
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
