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. Paolo
