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

["Denis V. Lunev" <den-lists@parallels.com>]

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On 07/23/2015 01:09 PM, Christian Borntraeger wrote:
> 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.
>

this seems a good idea to me, we are always changing
from threads to native in our installations

>> ---
>>   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;
>>
>


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