[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCHv1] x86: don't schedule when handling #NM exception
On 03/17/2014 05:19 AM, George Dunlap wrote: > On Mon, Mar 17, 2014 at 3:33 AM, H. Peter Anvin <hpa@xxxxxxxxx> wrote: >> No, the right thing is to unf*ck the Xen braindamage and use eagerfpu as a >> workaround for the legacy hypervisor versions. > > The interface wasn't an accident. In the most common case you'll want > to clear the bit anyway. In PV mode clearing it would require an extra > trip up into the hypervisor. So this saves one trip up into the > hypervisor on every context switch which involves an FPU, at the > expense of not being able to context-switch away when handling the > trap. > > -George > The interface was a complete faceplant, because it caused failures. You're not infinitely unconstrained since you want to play in the same sandbox as the native architecture, and if you want to have a hope of avoiding these kinds of failures you really need to avoid making random "improvements", certainly not without an explicit guest opt-in (the same we do for the native CPU architecture when adding new features.) So if this interface wasn't an accident it was active negligence and incompetence. -hpa _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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