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Re: [Qemu-devel] [PATCH v4 0/5] handle vhost reset/start/stop correctly
From: |
Yuanhan Liu |
Subject: |
Re: [Qemu-devel] [PATCH v4 0/5] handle vhost reset/start/stop correctly |
Date: |
Thu, 12 Nov 2015 22:08:15 +0800 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Thu, Nov 12, 2015 at 03:33:41PM +0200, Michael S. Tsirkin wrote:
> On Wed, Nov 11, 2015 at 09:24:36PM +0800, Yuanhan Liu wrote:
> >
> > Patch 1 rename RESET_DEVICE back to RESET_OWNER
> >
> > Patch 2 introduced a new function: vhost_net_reset(), which is invoked
> > when reset happens, say, driver is unloaded (unbinded).
> >
> > Michael suggested to do that only when MQ is not negotiated.
> > However, reset happens no matter MQ is enabled or negotiated
> > or not, and we should give a sign to backend to reset some
> > device to a proper state after it happens.
>
> I don't think it's needed: we set all state at start anyway.
Agree with that.
>
> > Note that the message sent is still RESET_OWNER. It might not
> > be a good idea, but we could not simply rename it to RESET_DEVICE,
> > and maybe adding another RESET_DEVICE might be better.
>
> So modern clients don't need this at all. Old clients need something to
> stop device, but singling out reset is not a good idea: even if driver
> is unloaded, you need to do that. snabbswitch (ab)uses RESET_OWNER for
> this, so maybe RESET_OWNER should be renamed DISABLE_ALL, to just make
> it stop all queues.
>
> Does any dpdk version that was released respond to RESET_OWNER in some
> way? How exactly?
It just resets some states, such as closing call fd and kick fd,
unmapping buf from hugetlbfs from set_mem_table.
And, apparently we could do that on stop, too. So, from this pov, we
don't need RESET_OWNER.
>
> > Patch 3 and 4 send SET_PROTOCOL_FEATURES at start, just like we send
> > SET_FEATURES.
> >
> > Patch 5 send SET_VRING_ENABLE at start/stop
> >
> > Michael, I intended to send it when MQ is negotiated as you
> > suggested,
> > however, I found that VHOST_USER_PROTOCOL_F_MQ is defined in
> > vhost-user.c,
> > which is not accessible to vhost.c.
> >
> > Exporting it to vhost.h will resolve that, however, it's not a good
> > idea to move vhost user specific stuff to there. We could also
> > introduce
> > another vhost callback to test whether MQ is negotiated: I just
> > don't
> > think it's worthy.
> >
> > Hence, here I just used a simple test: invoke set_vring_enable()
> > just
> > when it is defined. Judging the callback self has another MQ check,
> > I guess it's okay.
> >
> > And sorry that it took so long to send this version.
>
> Hmm, you are saying everyone needs SET_VRING_ENABLE?
> Maybe we should make SET_VRING_ENABLE depend on protocol features then,
> and not MQ?
I'm thinking something same. Otherwise, there is still no way to inform
the backend (or client) when a vhost dev is stopped when MQ is disabled
(which is the default state).
So, let's assume all clients have protocol features enabled, and send
SET_VRING_ENABLE at start/stop? And if it does not, it's just like we
are back to QEMU v2.3, where no RESET_OWNER nor SET_VRING_ENABLE
messages are sent on stop: it worked before, and it should also work
now.
>
> I applied patches 1 and 5 for now.
Do you have comment about patch 3 and 4? Should we set protocol features
just like we set features at start?
Thanks.
--yliu
- [Qemu-devel] [PATCH v4 0/5] handle vhost reset/start/stop correctly, Yuanhan Liu, 2015/11/11
- [Qemu-devel] [PATCH v4 3/5] vhost: introduce vhost_set/get_protocol_features callbacks, Yuanhan Liu, 2015/11/11
- [Qemu-devel] [PATCH v4 2/5] vhost: reset vhost net when virtio_net_reset happens, Yuanhan Liu, 2015/11/11
- [Qemu-devel] [PATCH v4 1/5] vhost: rename RESET_DEVICE backto RESET_OWNER, Yuanhan Liu, 2015/11/11
- [Qemu-devel] [PATCH v4 4/5] vhost: send SET_PROTOCOL_FEATURES at start, Yuanhan Liu, 2015/11/11
- [Qemu-devel] [PATCH v4 5/5] vhost: send SET_VRING_ENABLE at start/stop, Yuanhan Liu, 2015/11/11
- Re: [Qemu-devel] [PATCH v4 0/5] handle vhost reset/start/stop correctly, Michael S. Tsirkin, 2015/11/12
- Re: [Qemu-devel] [PATCH v4 0/5] handle vhost reset/start/stop correctly,
Yuanhan Liu <=