From: Maxime Coquelin <maxime.coquelin@redhat.com>
To: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Cc: "Zhiyong Yang" <zhiyong.yang@intel.com>,
dev@dpdk.org, ciara.loftus@intel.com,
"Marc-André Lureau" <mlureau@redhat.com>
Subject: Re: [dpdk-dev] [PATCH] vhost: fix MQ fails to startup
Date: Thu, 27 Apr 2017 10:52:20 +0200 [thread overview]
Message-ID: <0bb0c833-1178-c587-8085-12137ebd91d5@redhat.com> (raw)
In-Reply-To: <20170427082047.GL11512@yliu-dev.sh.intel.com>
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
>
next prev parent reply other threads:[~2017-04-27 8:52 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-27 6:34 Zhiyong Yang
2017-04-27 7:41 ` Loftus, Ciara
2017-04-27 7:56 ` Maxime Coquelin
2017-04-27 8:05 ` Maxime Coquelin
2017-04-27 8:24 ` Yang, Zhiyong
2017-04-27 8:32 ` Maxime Coquelin
2017-04-27 8:20 ` Yuanhan Liu
2017-04-27 8:52 ` Maxime Coquelin [this message]
2017-04-28 2:25 ` Yuanhan Liu
2017-04-28 7:23 ` Maxime Coquelin
2017-04-28 7:35 ` Yuanhan Liu
2017-04-28 7:39 ` Yuanhan Liu
2017-04-28 7:57 ` Maxime Coquelin
2017-04-28 8:00 ` Yuanhan Liu
2017-04-27 8:12 ` Yuanhan Liu
2017-04-27 8:32 ` Yang, Zhiyong
2017-04-27 9:41 ` [dpdk-dev] [PATCH v2] vhost: workaround " Zhiyong Yang
2017-04-27 10:00 ` Maxime Coquelin
2017-04-28 4:29 ` Yuanhan Liu
2017-05-10 2:07 ` Yang, Zhiyong
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