[Qemu-block] [PATCH RFC 0/2] Fix slow startup with many disks

[Alexander Yarygin]

During reset the aio_poll() function is called at least amount_of_disks^2 times:

for_each disk
    virtio_blk_reset()
        bdrv_drain_all()
                for_each disk
                         aio_poll()

For example, startup with 1000 disks takes over 13 minutes.

Patch 1/2 removes inner loop by using bdrv_drain() instead of bdrv_drain_all().
bdrv_drain() works on one disk at time.

Since bdrv_drain_all() is still called in other places, patch 2/2 optimizes
it for cases, where there are more disks than iothreads.

Thanks.

Alexander Yarygin (2):
  block-backend: Introduce blk_drain() and replace blk_drain_all()
  block: Let bdrv_drain_all() to call aio_poll() for each AioContext

 block/block-backend.c          |  5 +++++
 block/io.c                     | 42 ++++++++++++++++++++++++++----------------
 hw/block/virtio-blk.c          |  2 +-
 include/sysemu/block-backend.h |  1 +
 4 files changed, 33 insertions(+), 17 deletions(-)

-- 
1.9.1