Re: [Xen-devel] [PATCH MINI-OS] xenbus: notify the other end when necessary

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Oct 26, 2015 at 01:21:51PM +0100, Samuel Thibault wrote:
> Wei Liu, le Mon 26 Oct 2015 12:14:43 +0000, a écrit :
> > In my patch, mini-os notifies remote whenever it consumes a message,
> > which I think it's slightly better because backend can start putting
> > things in the ring as mini-os processes them.
> 
> That makes more notifications, but that can lead to more pipelining
> indeed.  That's what the Linux driver does, so let's do the same.
> 
> Also, I'm realizing: aren't we missing a full memory barrier between
> the memcpy_from_ring call and xenstore_buf->rsp_cons += ? (in the two
> places) We need to make sure to have finished copying from the ring
> before writing the new rsp_cons.
> 

You're right.

I think we should just turn that wmb() into two mb()s and place them
before xenstore_buf->rsp_cons +=.

Wei.

> Samuel

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