Re: [Qemu-devel] Re: [PATCH] vhost: fix features ack

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Mar 31, 2010 at 03:38:05PM -0300, Luiz Capitulino wrote:
> On Wed, 31 Mar 2010 13:26:23 -0500
> Anthony Liguori <anthony@codemonkey.ws> wrote:
> 
> > On 03/31/2010 01:20 PM, Michael S. Tsirkin wrote:
> > > From: David L Stevens<dlstevens@us.ibm.com>
> > >
> > > vhost driver in qemu didn't ack features, and this happens
> > > to work because we don't really require any features. However,
> > > it's better not to rely on this. This patch passes features to
> > > vhost as guest acks them.
> > >
> > > Signed-off-by: David L Stevens<dlstevens@us.ibm.com>
> > > Signed-off-by: Michael S. Tsirkin<mst@redhat.com>
> > > ---
> > >
> > > Anthony, here's a fixup patch to address an issue in vhost
> > > patches. Incidentially, what's the status of the vhost patchset?
> > >    
> > 
> > http://repo.or.cz/w/qemu/aliguori-queue.git vhost
> > 
> > Is what I'm currently testing.  With vhost disabled,  the following seg 
> > faults:
> > 
> > qemu-system-x86_64 -hda ~/images/linux.img -net tap -net 
> > nic,model=virtio -enable-kvm
> > 
> > But not when using TCG.  I'm not sure that it's your patches at fault 
> > and I'm attempting to bisect now to figure that out.
> 
>  Probably this is the same segfault I'm getting right now in master,
> bisect says it's:
> 
> """
> commit ad96090a01d848df67d70c5259ed8aa321fa8716
> Author: Blue Swirl <blauwirbel@gmail.com>
> Date:   Mon Mar 29 19:23:52 2010 +0000
> 
>     Refactor target specific handling, compile vl.c only once
> """

Why are the compile once patches helpful? They seem to introduce
churn and bugs, they actively make it harder to extend qemu as you can't use
target-specific code in code that is compiled once, they might have
performance penalty - and what do we gain? Any given user is unlikely to
need to build on more than one target, distros have enough computing
power to build in parallel.

Maybe it makes sense to revert the compile once patches, and discuss
these issues before re-commit?

-- 
MST