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aio: only account I/O wait time in read_events if there are active requests

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On 2.6.24, top started showing 100% iowait on one CPU when a UML instance was
running (but completely idle).  The UML code sits in io_getevents waiting for
an event to be submitted and completed.

Fix this by checking ctx->reqs_active before scheduling to determine whether
or not we are waiting for I/O.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Cc: Zach Brown <zach.brown@oracle.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jeff Moyer 2007-12-04 23:45:02 -08:00 committed by Linus Torvalds
parent e3c0ac04f9
commit e00ba3dae0
1 changed files with 6 additions and 1 deletions
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7
fs/aio.c
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@ -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;