On 04/27/2017 10:20 AM, Yuanhan Liu wrote:
On Thu, Apr 27, 2017 at 09:56:47AM +0200, Maxime Coquelin wrote:
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.
Wouldn't that be an overkill, judging that REPLY_ACK is not a must
feature?
Yes, maybe. But it was introduced to fix (possible) race conditions:
https://lists.gnu.org/archive/html/qemu-devel/2016-07/msg06173.html
Note that I planned to use this feature for the device IOTLB
implementation to let the backend decide whether it wants the IOTLB
misses synchronous or asynchronous. But I can still change the protocol
spec to make this behavior specific to this request.
Maxime
--yliu
