[dpdk-dev] [PATCH] vhost: fix MQ fails to startup

[Maxime Coquelin]

Hi Zhiyong,

+Marc-André

On 04/27/2017 08:34 AM, Zhiyong Yang wrote:
> vhost since dpdk17.02 + qemu2.7 and above will cause failures of
> new connection when negotiating to set MQ. (one queue pair works
> well).Because there exist some bugs in qemu code when introducing
> VHOST_USER_PROTOCOL_F_REPLY_ACK to qemu. when dealing with the vhost
> message VHOST_USER_SET_MEM_TABLE for the second time, qemu indeed
> doesn't send the messge (The message needs to be sent only once)but
> still will be waiting for dpdk's reply ack, then, qemu is always
> freezing. DPDK code works in the right way.

I'm looking at Qemu's vhost_user_set_mem_table() function, but fail to
see how it could wait for the reply-ack if it didn't send the
VHOST_USER_SET_MEM_TABLE request before.

> But the feature
> VHOST_USER_PROTOCOL_F_REPLY_ACK has to be disabled by default at the
> dpdk side in order to avoid the feature support of DPDK + qemu at
> the same time. if doing like that, MQ can works well. Once Qemu bugs
> have been fixed and upstreamed, we can enable it.

The problem is for DPDK to detect whether bug is fixed in Qemu.
Maybe only way would be to have a new protocol feature flag, which is
not really its role.

> Fixes: 73c8f9f69c6c("vhost: introduce reply ack feature")
> 
> Reported-by: Loftus, Ciara <ciara.loftus at intel.com>
> Signed-off-by: Zhiyong Yang <zhiyong.yang at intel.com>
> ---
>   lib/librte_vhost/vhost_user.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/librte_vhost/vhost_user.h b/lib/librte_vhost/vhost_user.h
> index 2ba22db..a3d2900 100644
> --- a/lib/librte_vhost/vhost_user.h
> +++ b/lib/librte_vhost/vhost_user.h
> @@ -52,7 +52,7 @@
>   #define VHOST_USER_PROTOCOL_FEATURES	((1ULL << VHOST_USER_PROTOCOL_F_MQ) | \
>   					 (1ULL << VHOST_USER_PROTOCOL_F_LOG_SHMFD) |\
>   					 (1ULL << VHOST_USER_PROTOCOL_F_RARP) | \
> -					 (1ULL << VHOST_USER_PROTOCOL_F_REPLY_ACK) | \
> +					 (0ULL << VHOST_USER_PROTOCOL_F_REPLY_ACK) | \
>   					 (1ULL << VHOST_USER_PROTOCOL_F_NET_MTU))
>   
>   typedef enum VhostUserRequest {
> 

Cheers,
Maxime