On Wed, 29 Feb 2012 10:15:53 +0200 Alon Levy <al...@redhat.com> wrote:
> On Tue, Feb 28, 2012 at 05:10:39PM -0300, Luiz Capitulino wrote: > > On Sat, 25 Feb 2012 10:46:07 +0200 > > Alon Levy <al...@redhat.com> wrote: > > > > > On Fri, Feb 24, 2012 at 04:40:15PM -0600, Anthony Liguori wrote: > > > > On 02/24/2012 03:22 PM, Alon Levy wrote: > > > > >This is an across the board change since I wanted to keep the existing > > > > >(good imo) single graphic_console_init callback setter, instead of > > > > >introducing a new cb that isn't set by it but instead by a second > > > > >initialization function. > > > > > > > > > >Signed-off-by: Alon Levy<al...@redhat.com> > > > > > > > > What's the rationale for this? > > > > > > There is a hang possible with the current screendump command, qxl, a > > > spice client using libvirt and spice-gtk such as virt-viewer / > > > remote-viewer, where you have: > > > 1. libvirt waiting for screendump to complete > > > 2. screendump waiting for spice server thread to render > > > 3. spice server thread waiting for spice client to read messages > > > > Which messages? > > spice display channel messages. > > > > > > 4. spice client == libvirt client, waiting for screendump completion > > > > The way I had understood this problem is that qxl takes a long time to > > perform a screen dump, which would cause the global mutex to be held for > > a long time. If this is really serious, then a async command for it > > makes sense IMO. > > That is true, but it is not the immediate problem the bz is dealing with > - if it was only this there would be no hang. Well, this kind of hang always smells like a spice threading synchronization problem to me. I thought that I'd be capable of showing that if I really understood what was going on, but I can't, even with your diagram. An asynchronous command solves the global mutex contention problem, but I think this hang should be further investigated, otherwise the async command risks just hiding the real problem.
