From: Yuanhan Liu <yuanhan.liu@linux.intel.com>
To: "Tan, Jianfeng" <jianfeng.tan@intel.com>
Cc: dev@dpdk.org, zhihong.wang@intel.com, lining18@jd.com
Subject: Re: [dpdk-dev] [PATCH 2/3] net/virtio_user: fix wrong sequence of messages
Date: Fri, 9 Sep 2016 12:19:49 +0800 [thread overview]
Message-ID: <20160909041949.GP23158@yliu-dev.sh.intel.com> (raw)
In-Reply-To: <11291eac-cbbe-7080-3d35-bdacb5341d89@intel.com>
On Fri, Sep 09, 2016 at 11:59:18AM +0800, Tan, Jianfeng wrote:
> It's actually a good catch. After a light thought, I think in DPDK vhost, we
> may need to create those virtqueues once unix socket gets connected, just
> like in vhost-net, virtqueues are created on char file open. Right?
>
> There is a difference: for vhost-net and tap mode, IIRC, it knows how
> many queues before doing setup.
>
> No, from linux/drivers/vhost/net.c:vhost_net_open(), we can see that
> virtqueues are allocated according to VHOST_NET_VQ_MAX.
>
> Well, if you took a closer look, you will find VHOST_NET_VQ_MAX is
> defined to 2. That means it allocates a queue-pair only.
>
> And FYI, the MQ support for vhost-net is actually done in the tap
> driver, but not in vhost-net driver. That results to the MQ
> implementation is a bit different between vhost-net and vhost-user.
>
> Put simply, in vhost-net, one queue-pair has a backend fd associated
> with it. Vhost requests for different queue-pair are sent by different
> fd. That also means the vhost-net doesn't even need be aware of the
> MQ stuff.
>
> However, for vhost-user implementation, all queue-pairs share one
> socket fd. All requests all also sent over the single socket fd,
> thus the backend (DPDK vhost) has to figure out how many queue
> pairs are actually enabled: and we detect it by reading the
> vring index of SET_VRING_CALL message; it's not quite right though.
>
>
> Aha, right, nice analysis.
Just some rough memory in my mind ;-)
>
>
>
> How about reconsidering previous suggestion to allocate vq once connection
> is established?
>
> That's too much, because DPDK claims to support up to 0x8000
> queue-pairs. Don't even to say that the vhost_virtqueue struct
> was way too big before: it even holds an array of buf_vec with
> size 256.
>
>
> Another mistake of my memory, I was remember it wrongly as only 8 VQs are
> supported.
> One thing not related, provided that VHOST_MAX_QUEUE_PAIRS equals to 0x8000,
> struct vhost_virtqueue *virtqueue[VHOST_MAX_QUEUE_PAIRS * 2] spends 4MB for
> each virtio device, which could be a refined.
Yes, we could allocate a small array first, and then re-allocate if
necessary.
>
>
>
> Never mind, above fix on the vhost side will not take effect on existing
> vpp-vhost implementations.
>
> Actually, I was talking about the DPDK vhost implementation :)
>
>
> This patch is talking about vpp's native vhost implementation, not dpdk-vhost,
> and not the way vpp uses dpdk-vhost.
Yes, I know. What I meant is there was a "workaround" in DPDK vhost
implementation, and since you bring this issue on the table again,
it's a chance to think about how can we fix it.
A rough idea come to my mind is we could check all the per-vring message
at the begining of vhost_user_msg_handler() and allocate related vq when
necessary (when it's the first vring message we got).
Yeah, I know it's a bit ugly, but it at least gets rid of that "not-that-true"
assumption.
>
> Still not working. VPP needs SET_VRING_CALL to create vq firstly.
>
> Didn't get it. In the proposal, SET_FEATURES is sent before every other
> messages, thus it should not cause the issue you described in this patch.
>
>
> OK. Let me try to explain. We take three vhost implementations into
> consideration: dpdk-2.2-vhost, dpdk-master-vhost, vpp-native-vhost.
>
> If set_feature before set_vring_call, dpdk-2.2-vhost will fail: inside
> set_feature handler, assigning header length to VQs which will be created in
> set_vring_call handler.
Oh, right. That was an in-correct implementation.
> So we need to keep set_vring_call firstly.
> Then set_feature needs to be sent
> before any other msgs, this is what vpp-native-vhost requires. In all, the
> sequence is like this:
> 1. set_vring_call,
> 2. set_feature,
> 3. other msgs
>
>
> Besides, haven't we already sent SET_VRING_CALL before other messages
> (well, execept the SET_FEATURES and SET_MEM_TABLE message)?
>
>
> Yes, set_vring_call is already in the first place, but we need to plugin
> set_feature between set_vring_call and other msgs. Previously, set_vring_call
> and other msgs are together.
Okay. Another thing I noticed is that virtio-user lacks some feature
negotiations, like GET_FEATURES and GET_PROTOCOL_FEATURES. I think you
might need add them back somewhen?
--yliu
next prev parent reply other threads:[~2016-09-09 4:19 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-05 11:36 [dpdk-dev] [PATCH 0/3] fix virtio_user issues Jianfeng Tan
2016-08-05 11:36 ` [dpdk-dev] [PATCH 1/3] net/virtio_user: fix queue pair not enabled Jianfeng Tan
2016-09-06 6:30 ` Yuanhan Liu
2016-08-05 11:36 ` [dpdk-dev] [PATCH 2/3] net/virtio_user: fix wrong sequence of messages Jianfeng Tan
2016-08-05 16:36 ` Stephen Hemminger
2016-08-08 1:19 ` Tan, Jianfeng
2016-09-06 6:42 ` Yuanhan Liu
2016-09-06 7:54 ` Tan, Jianfeng
2016-09-06 8:20 ` Yuanhan Liu
2016-09-08 8:53 ` Tan, Jianfeng
2016-09-08 12:18 ` Yuanhan Liu
2016-09-09 3:59 ` Tan, Jianfeng
2016-09-09 4:19 ` Yuanhan Liu [this message]
2016-09-09 5:50 ` Tan, Jianfeng
2016-09-09 6:03 ` Yuanhan Liu
2016-09-09 6:24 ` Tan, Jianfeng
2016-09-09 6:31 ` Yuanhan Liu
2016-08-05 11:36 ` [dpdk-dev] [PATCH 3/3] net/virtio_user: fix dev not freed after init error Jianfeng Tan
2016-08-05 16:34 ` Stephen Hemminger
2016-08-08 1:07 ` Tan, Jianfeng
2016-08-29 7:01 ` [dpdk-dev] [PATCH 0/3] fix virtio_user issues Christian Ehrhardt
2016-09-27 19:11 ` [dpdk-dev] [PATCH v2 " Jianfeng Tan
2016-09-27 19:11 ` [dpdk-dev] [PATCH v2 1/3] net/virtio_user: fix queue pair not enabled Jianfeng Tan
2016-09-28 0:05 ` Yuanhan Liu
2016-09-27 19:11 ` [dpdk-dev] [PATCH v2 2/3] net/virtio_user: fix wrong sequence of messages Jianfeng Tan
2016-09-27 19:11 ` [dpdk-dev] [PATCH v2 3/3] net/virtio_user: fix dev not freed after init error Jianfeng Tan
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