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Re: [Qemu-devel] [PATCH 1/4] block: Remove blk_pread_unthrottled()
From: |
Max Reitz |
Subject: |
Re: [Qemu-devel] [PATCH 1/4] block: Remove blk_pread_unthrottled() |
Date: |
Fri, 26 Jul 2019 11:18:52 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 |
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 <address@hidden>
> ---
> 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 <address@hidden>
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