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

[Christian Borntraeger <borntraeger@de.ibm.com>]

Am 10.06.2015 um 13:38 schrieb Alexander Yarygin:
> 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(-)
> 

Whole series is 
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>

I think we can remove the RFC. I would like to see this for 2.4.

Christian