Re: [Qemu-block] [PATCH 06/19] block: Avoid unnecessary aio_poll() in AIO_WAIT_WHILE()

[Stefan Hajnoczi]

On Wed, Apr 11, 2018 at 06:39:27PM +0200, Kevin Wolf wrote:
> Commit 91af091f923 added an additional aio_poll() to BDRV_POLL_WHILE()
> in order to make sure that all pending BHs are executed on drain. This
> was the wrong place to make the fix, as it is useless overhead for all
> other users of the macro and unnecessarily complicates the mechanism.
> 
> This patch effectively reverts said commit (the context has changed a
> bit and the code has moved to AIO_WAIT_WHILE()) and instead polls in the
> loop condition for drain.
> 
> The effect is probably hard to measure in any real-world use case
> because actual I/O will dominate, but if I run only the initialisation
> part of 'qemu-img convert' where it calls bdrv_block_status() for the
> whole image to find out how much data there is copy, this phase actually
> needs only roughly half the time after this patch.
> 
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
>  include/block/aio-wait.h | 22 ++++++++--------------
>  block/io.c               | 11 ++++++++++-
>  2 files changed, 18 insertions(+), 15 deletions(-)

Reviewed-by: Stefan Hajnoczi <address@hidden>

signature.asc
Description: PGP signature