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Re: [Qemu-block] [Qemu-devel] [PATCH v2 1/2] raw-posix: warn about BDRV_
From: |
Christian Borntraeger |
Subject: |
Re: [Qemu-block] [Qemu-devel] [PATCH v2 1/2] raw-posix: warn about BDRV_O_NATIVE_AIO if libaio is unavailable |
Date: |
Thu, 23 Jul 2015 12:09:25 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 |
Am 17.07.2015 um 16:23 schrieb Stefan Hajnoczi:
> raw-posix.c silently ignores BDRV_O_NATIVE_AIO if libaio is unavailable.
> It is confusing when aio=native performance is identical to aio=threads
> because the binary was accidentally built without libaio.
>
> Print a deprecation warning if -drive aio=native is used with a binary
> that does not support libaio. There are probably users using aio=native
> who would be inconvenienced if QEMU suddenly refused to start their
> guests. In the future this will become an error.
>
> Signed-off-by: Stefan Hajnoczi <address@hidden>
had that myself on a freshly installed system without libaio-devel.
Acked-by: Christian Borntraeger <address@hidden>
Another thing. Would it make sense to change the default to aio=native somewhen?
>From what I can tell this seems to outperform aio=threads in most cases.
> ---
> block/raw-posix.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/block/raw-posix.c b/block/raw-posix.c
> index 855febe..e09019c 100644
> --- a/block/raw-posix.c
> +++ b/block/raw-posix.c
> @@ -519,7 +519,16 @@ static int raw_open_common(BlockDriverState *bs, QDict
> *options,
> "future QEMU versions.\n",
> bs->filename);
> }
> -#endif
> +#else
> + if (bdrv_flags & BDRV_O_NATIVE_AIO) {
> + error_printf("WARNING: aio=native was specified for '%s', but "
> + "is not supported in this build. Falling back to "
> + "aio=threads.\n"
> + " This will become an error condition in "
> + "future QEMU versions.\n",
> + bs->filename);
> + }
> +#endif /* !defined(CONFIG_LINUX_AIO) */
>
> s->has_discard = true;
> s->has_write_zeroes = true;
>