review-2.6.22.y/aio-only-account-IO-wait-time-in-read_events-if-there-are-active-requests.patch

   1 From e00ba3dae077f54cfd2af42e939a618caa7a3bca Mon Sep 17 00:00:00 2001
   2 From: Jeff Moyer <jmoyer@redhat.com>
   3 Date: Tue, 4 Dec 2007 23:45:02 -0800
   4 Subject: [PATCH] aio: only account I/O wait time in read_events if there are active requests
   5
   6 On 2.6.24, top started showing 100% iowait on one CPU when a UML instance was
   7 running (but completely idle).  The UML code sits in io_getevents waiting for
   8 an event to be submitted and completed.
   9
  10 Fix this by checking ctx->reqs_active before scheduling to determine whether
  11 or not we are waiting for I/O.
  12
  13 Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
  14 Cc: Zach Brown <zach.brown@oracle.com>
  15 Cc: Miklos Szeredi <miklos@szeredi.hu>
  16 Cc: Jeff Dike <jdike@addtoit.com>
  17 Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
  18 Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
  19 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  20 Signed-off-by: Oliver Pinter <oliver.pntr@gmail.com>
  21
  22
  23 diff --git a/fs/aio.c b/fs/aio.c
  24 index f12db41..9dec7d2 100644
  25 --- a/fs/aio.c
  26 +++ b/fs/aio.c
  27 @@ -1161,7 +1161,12 @@ retry:
  28                         ret = 0;
  29                         if (to.timed_out)       /* Only check after read evt */
  30                                 break;
  31 -                       io_schedule();
  32 +                       /* Try to only show up in io wait if there are ops
  33 +                        *  in flight */
  34 +                       if (ctx->reqs_active)
  35 +                               io_schedule();
  36 +                       else
  37 +                               schedule();
  38                         if (signal_pending(tsk)) {
  39                                 ret = -EINTR;
  40                                 break;