[libvirt] [Spice-devel] [PATCH v4] qemu: Use heads parameter for QXL driver

Christophe Fergeau cfergeau at redhat.com
Tue Jul 21 07:09:38 UTC 2015


On Mon, Jul 20, 2015 at 11:25:52AM +0200, Martin Kletzander wrote:
> In the meantime, is the only thing this does limiting the maximum?  Is
> it there just to save some memory or why?  Because otherwise I can't
> see the use-case in that.  I'm not saying there isn't one, just that I
> can't find it.  And I even looked under the fridge :)

There are 2 main uses for this feature:
- first, it's indeed to help in setting up guest memory size, you need a
  bit more than 16MB of VRAM per full-HD display that you want your
  guest to support, and the failure modes when the guest tries to go
  over that limit are not explicit at all. Thus it can be helpful to
  enforce the limitation to just 1 monitor if you don't want to assign a
  lot of VRAM to your guest
- the second one is more cosmetic, management innterfaces (oVirt) let
  you select the number of screens you want in the VM, but at the moment
  it's not used at all on the SPICE client side, you always get a list
  of 4 displays which you can enable in one of the client menus. After
  the work Frediano has done, you only see 1 entry in that client menu
  if you said in the VM XML that you only want 1 head.

Hope that helps,

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