Re: [Qemu-devel] [PATCH 0/6] block: do request processing in a coroutine

[Kevin Wolf <kwolf@redhat.com>]

Am 05.10.2011 18:17, schrieb Stefan Hajnoczi:
> Block layer features like dirty block tracing, I/O throttling, and live block
> copy are forced to duplicate code due to the three different interfaces:
> synchronous, asynchronous, and coroutines.
> 
> Since there are bdrv_read(), bdrv_aio_readv(), and bdrv_co_readv() interfaces
> for read (and similar for write), per-request processing needs to be duplicated
> for each of these execution contexts.  For example, dirty block tracking code
> is duplicated across these three interfaces.
> 
> This patch series unifies request processing so that there is only one code
> path.  I see this as a prerequisite to the live block copy (image streaming)
> code I am working on, so I'm pushing it now.
> 
> The short-term win from this series is that it becomes easy to add live block
> copy and other features.  We now have a single code path where the perf-request
> processing is done.
> 
> The longer-term win will be dropping the BlockDriver .bdrv_read(),
> .bdrv_write(), .bdrv_aio_readv(), and .bdrv_aio_writev() interfaces.  By doing
> that we can bring all BlockDrivers onto a common interface, namely
> .bdrv_co_readv() and .bdrv_co_writev().  It will also allow us to drop most of
> the sync and aio emulation code.
> 
> A consequence of this patch series is that every I/O request goes through at
> least one coroutine.  There is no longer a direct .bdrv_read(), .bdrv_write(),
> .bdrv_aio_readv(), or .bdrv_aio_writev() call - we're trying to phase out those
> interfaces.  I have not noticed performance degradation in correctness tests
> but we need to confirm that there has not been a performance regression.
> 
> Stefan Hajnoczi (6):
>   block: directly invoke .bdrv_aio_*() in bdrv_co_io_em()
>   block: split out bdrv_co_do_readv() and bdrv_co_do_writev()
>   block: switch bdrv_read()/bdrv_write() to coroutines
>   block: switch bdrv_aio_readv() to coroutines
>   block: mark blocks dirty on coroutine write completion
>   block: switch bdrv_aio_writev() to coroutines
> 
>  block.c |  273 +++++++++++++++++++++++++++++++--------------------------------
>  1 files changed, 134 insertions(+), 139 deletions(-)
> 

Except for breaking synchronous drivers this looks good.

I have applied the first two patches to the block branch, so if you
don't need to change them, submitting patches 3-6 for v2 will be enough.

Kevin