[Qemu-devel] [PATCH RFC v2 0/3] Fix slow startup with many disks

[Alexander Yarygin <yarygin@linux.vnet.ibm.com>]

Changes in v2:
    - Patch "block-backend: Introduce blk_drain() and replace blk_drain_all()"
      splitted to two.
    - blk_drain() moved to above virtio_blk_data_plane_stop().

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.

Patches 1 and 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 3 optimizes
it for cases, where there are more disks than iothreads.

Thanks.

Alexander Yarygin (3):
  block-backend: Introduce blk_drain()
  virtio-blk: Use blk_drain() to drain IO requests
  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          | 11 ++++++-----
 include/sysemu/block-backend.h |  1 +
 4 files changed, 38 insertions(+), 21 deletions(-)

-- 
1.9.1