Re: [Qemu-devel] [PATCH 01/12] block: Don't disable I/O throttling on sync requests

From: Eric Blake <eblake@redhat.com>
To: Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org
Cc: berto@igalia.com, qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH 01/12] block: Don't disable I/O throttling on sync requests
Date: Tue, 22 Mar 2016 15:40:09 -0600	[thread overview]
Message-ID: <56F1BBB9.8060908@redhat.com> (raw)
In-Reply-To: <1458660792-3035-2-git-send-email-kwolf@redhat.com>

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On 03/22/2016 09:33 AM, Kevin Wolf wrote:
> We had to disable I/O throttling with synchronous requests because we
> didn't use to run timers in nested event loops when the code was
> introduced. This isn't true any more, and throttling works just fine
> even when using the synchronous API.
> 
> The removed code is in fact dead code since commit a8823a3b ('block: Use
> blk_co_pwritev() for blk_write()') because I/O throttling can only be
> set on the top layer, but BlockBackend always uses the coroutine
> interface now instead of using the sync API emulation in block.c.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/io.c | 11 -----------
>  1 file changed, 11 deletions(-)
> 
> diff --git a/block/io.c b/block/io.c
> index cce508a..e4438da 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -561,17 +561,6 @@ static int bdrv_prwv_co(BlockDriverState *bs, int64_t offset,
>          .flags = flags,
>      };
>  
> -    /**
> -     * In sync call context, when the vcpu is blocked, this throttling timer
> -     * will not fire; so the I/O throttling function has to be disabled here
> -     * if it has been enabled.
> -     */
> -    if (bs->io_limits_enabled) {
> -        fprintf(stderr, "Disabling I/O throttling on '%s' due "
> -                        "to synchronous I/O.\n", bdrv_get_device_name(bs));

And we get rid of an fprintf().  Nice bonus.

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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