Re: [Qemu-devel] [PATCH v2 1/2] raw-posix: warn about BDRV_O_NATIVE_AIO if libaio is unavailable

[Christian Borntraeger <borntraeger@de.ibm.com>]

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 <stefanha@redhat.com>

had that myself on a freshly installed system without libaio-devel.
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>


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;
>