Re: [PATCH V7 4/4 net-next] vhost: vhost TX zero-copy support

On Wed, 2011-06-29 at 12:13 +0300, Michael S. Tsirkin wrote:

On Sat, May 28, 2011 at 12:34:27PM -0700, Shirley Ma wrote:

quoted

Hello Michael,

In order to use wait for completion in shutting down, seems to me
another work thread is needed to call vhost_zerocopy_add_used,

Hmm I don't see vhost_zerocopy_add_used here.

I put the call in vhost_set_vring.

quoted

it seems
too much work to address a minor issue here. Do we really need it?

Assuming you mean vhost_zerocopy_signal_used, here's how I would do
it:
add a kref and a completion, signal completion in kref_put
callback, when backend is set - kref_get, on cleanup,
kref_put and then wait_for_completion_interruptible.
Where's the need for another thread coming from?

If you like, post a patch with busywait + a FIXME comment,
and I can write up a patch on top.

I might not have time  to finish this during my vacation, so I am
putting busywait + a FIXME comment.

(BTW, ideally the function that does the signalling should be
in core networking bits so that it's still around
even if the vhost module gets removed). 

Thanks
Shirley