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block: clean up bdrv_drain_all() throttling comments

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Since cc0681c45430a1f1a4c2d06e9499b7775afc9a18 ("block: Enable the new
throttling code in the block layer.") bdrv_drain_all() no longer spins.
The code used to look as follows:

  do {
      busy = qemu_aio_wait();

      /* FIXME: We do not have timer support here, so this is effectively
       * a busy wait.
       */
      QTAILQ_FOREACH(bs, &bdrv_states, list) {
          while (qemu_co_enter_next(&bs->throttled_reqs)) {
              busy = true;
          }
      }
  } while (busy);

Note that throttle requests are kicked but I/O throttling limits are
still in effect.  The loop spins until the vm_clock time allows the
request to make progress and complete.

The new throttling code introduced bdrv_start_throttled_reqs().  This
function not only kicks throttled requests but also temporarily disables
throttling so requests can run.

The outdated FIXME comment can be removed.  Also drop the busy = true
assignment since we overwrite it immediately afterwards.

Reviewed-by: Alex Bligh <alex@alex.org.uk>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2013-11-26 16:18:00 +01:00
parent ac95acdb8e
commit 0b06ef3bdd
1 changed files with 1 additions and 6 deletions
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7
block.c
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@ -1557,13 +1557,8 @@ void bdrv_drain_all(void)
BlockDriverState *bs;
while (busy) {
/* FIXME: We do not have timer support here, so this is effectively
* a busy wait.
*/
QTAILQ_FOREACH(bs, &bdrv_states, list) {
if (bdrv_start_throttled_reqs(bs)) {
busy = true;
}
bdrv_start_throttled_reqs(bs);
}
busy = bdrv_requests_pending_all();