On Fri, Feb 08, 2013 at 12:52:12PM +0100, Paolo Bonzini wrote: > Il 07/02/2106 07:28, Luigi Rizzo ha scritto: > > On Fri, Feb 08, 2013 at 11:46:34AM +0100, Paolo Bonzini wrote: > >> Il 08/02/2013 11:20, Luigi Rizzo ha scritto: > > ... > >>> I am happy to make this default to off. But it would be good if you could > >>> actually give it a try. Note that linux and FreeBSD (and presumably > >>> windows) > >>> do use moderation by default so enabling the emulation of the > >>> registers makes the guest OS behave differently (and closer to bare > >>> metal). > >>> > >>> To test that the patch itself does not cause regression in the emulator > >>> one should also turn off moderation in the guest (one of the tests i > >>> have run). > >> > >> I think making the default on is fine, but you need to add compatibility > >> options to leave it off in older machine types (pc-1.4 and earlier). > > > > I am unclear on what you mean by "older machine types" ? > > The hardware (E1000_DEV_ID_82540EM) does have these registers, > > and it is entirely up to the guest OS to use them or not. > > Yes, but suppose a guest has a bug that was masked by the old > non-implementation. "-M pc-1.4" is supposed to bring back the old > version's behavior as much as possible, including making the guest bug > latent again.
ok i see. Is there some example code that already handles a similar '-M' option so i can look at it and use to set the mit_on parameter ? cheers luigi