Zach Brown <[email protected]> writes:
>> We could check ctx->reqs_active before scheduling to determine whether
>> or not we are waiting for I/O, but this would require taking the
>> context lock in order to be accurate. Given that the test would be
>> only for the sake of book keeping, it might be okay to do it outside
>> of the lock.
>>
>> Zach, what are your thoughts on this?
>
> I agree that it'd be OK to test it outside the lock, though we'll want
> some commentary:
>
> /* Try to only show up in io wait if there are ops in flight */
> if (ctx->reqs_active)
> io_schedule();
> else
> schedule();
>
> It's cheap, safe, and accurate the overwhelming majority of the time :).
>
> We only need it in read_events(). The other two io_schedule() calls are
> only reached to wait on pending reqs specifically.
>
> It still won't make sense for iocbs which aren't performing IO, but I
> guess that's one more bridge to cross when we come to it.
>
> Do you want to throw this tiny patch together and submit it?
Sure. I tested this on a system that I used to reproduce the problem,
and it shows I/O Wait back at normal levels on an idle system with 1
uml guest running.
Andrew, do you need a separate email with a [patch] heading or will
this do?
Cheers,
Jeff
Only account I/O wait time in read_events if there are active
requests.
Signed-off-by: Jeff Moyer <[email protected]>
diff --git a/fs/aio.c b/fs/aio.c
index f12db41..9dec7d2 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1161,7 +1161,12 @@ retry:
ret = 0;
if (to.timed_out) /* Only check after read evt */
break;
- io_schedule();
+ /* Try to only show up in io wait if there are ops
+ * in flight */
+ if (ctx->reqs_active)
+ io_schedule();
+ else
+ schedule();
if (signal_pending(tsk)) {
ret = -EINTR;
break;
--
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