Re: [Qemu-devel] [PATCH] xen: use native disk xenbus protocol if possible

[Juergen Gross]

On 29/06/16 17:20, Anthony PERARD wrote:
> On Fri, Jun 17, 2016 at 01:14:56PM +0200, Juergen Gross wrote:
>> The qdisk implementation is using the native xenbus protocol only in
>> case of no protocol specified at all. As using the explicit 32- or
>> 64-bit protocol is slower than the native one due to copying requests
>> not by memcpy but element for element, this is not optimal.
>>
>> Correct this by using the native protocol in case word sizes of
>> frontend and backend match.
>>
>> Signed-off-by: Juergen Gross <address@hidden>
>> ---
>>  hw/block/xen_disk.c | 16 ++++++++--------
>>  1 file changed, 8 insertions(+), 8 deletions(-)
>>
>> diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
>> index 2862b59..0961fcb 100644
>> --- a/hw/block/xen_disk.c
>> +++ b/hw/block/xen_disk.c
>> @@ -976,14 +976,14 @@ static int blk_connect(struct XenDevice *xendev)
>>          blkdev->feature_persistent = !!pers;
>>      }
>>  
>> -    blkdev->protocol = BLKIF_PROTOCOL_NATIVE;
>> -    if (blkdev->xendev.protocol) {
>> -        if (strcmp(blkdev->xendev.protocol, XEN_IO_PROTO_ABI_X86_32) == 0) {
>> -            blkdev->protocol = BLKIF_PROTOCOL_X86_32;
>> -        }
>> -        if (strcmp(blkdev->xendev.protocol, XEN_IO_PROTO_ABI_X86_64) == 0) {
>> -            blkdev->protocol = BLKIF_PROTOCOL_X86_64;
>> -        }
>> +    if (!blkdev->xendev.protocol) {
>> +        blkdev->protocol = BLKIF_PROTOCOL_NATIVE;
>> +    } else if (strcmp(blkdev->xendev.protocol, XEN_IO_PROTO_ABI_NATIVE) == 
>> 0) {
>> +        blkdev->protocol = BLKIF_PROTOCOL_NATIVE;
>> +    } else if (strcmp(blkdev->xendev.protocol, XEN_IO_PROTO_ABI_X86_32) == 
>> 0) {
>> +        blkdev->protocol = BLKIF_PROTOCOL_X86_32;
>> +    } else if (strcmp(blkdev->xendev.protocol, XEN_IO_PROTO_ABI_X86_64) == 
>> 0) {
>> +        blkdev->protocol = BLKIF_PROTOCOL_X86_64;
> 
> There is one difference with the previous code, in case the protocol is
> specified, but it not x86_32 or x86_64, then no blkdev->protocol is
> selected (then no ring is initialized). Could you re-add this case?

Aah, of course!

Thanks,

Juergen