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Revision 0b06ef3b

ID0b06ef3bdd17742ae50c0662d3fe8ed944648890

Added by Stefan Hajnoczi over 10 years ago

block: clean up bdrv_drain_all() throttling comments

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The outdated FIXME comment can be removed.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 <>
Signed-off-by: Stefan Hajnoczi <>

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