Re: [Qemu-devel] [PATCH 1/4] block: Remove blk_pread_unthrottled()

[Max Reitz <mreitz@redhat.com>]

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On 25.07.19 18:27, Kevin Wolf wrote:
> The functionality offered by blk_pread_unthrottled() goes back to commit
> 498e386c584. Then, we couldn't perform I/O throttling with synchronous
> requests because timers wouldn't be executed in polling loops. So the
> commit automatically disabled I/O throttling as soon as a synchronous
> request was issued.
> 
> However, for geometry detection during disk initialisation, we always
> used (and still use) synchronous requests even if guest requests use AIO
> later. Geometry detection was not wanted to disable I/O throttling, so
> bdrv_pread_unthrottled() was introduced which disabled throttling only
> temporarily.
> 
> All of this isn't necessary any more because we do run timers in polling
> loop and even synchronous requests are now using coroutine
> infrastructure internally. For this reason, commit 90c78624f already
> removed the automatic disabling of I/O throttling.
> 
> It's time to get rid of the workaround for the removed code, and its
> abuse of blk_root_drained_begin()/end(), as well.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  include/sysemu/block-backend.h |  2 --
>  block/block-backend.c          | 16 ----------------
>  hw/block/hd-geometry.c         |  7 +------
>  3 files changed, 1 insertion(+), 24 deletions(-)

It took me a bit of git blaming to find out more about the history of
timer execution (and finally arrived at
https://lists.nongnu.org/archive/html/qemu-devel/2013-08/msg03060.html),
but now I’m reasonably confident.

Reviewed-by: Max Reitz <mreitz@redhat.com>


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