* Zachary Amsden (zach at vmware.com) wrote: > The VMI ROM has a mode where hypercalls can be queued and batched. This turns > out to be a significant win during context switch, but must be done at a > specific point before side effects to CPU state are visible to subsequent > instructions. This is similar to the MMU batching hooks already provided. > The same hooks could be used by the Xen backend to implement a context switch > multicall. > > To explain a bit more about lazy modes in the paravirt patches, basically, the > idea is that only one of lazy CPU or MMU mode can be active at any given time. > Lazy MMU mode is similar to this lazy CPU mode, and allows for batching of > multiple PTE updates (say, inside a remap loop), but to avoid keeping some kind > of state machine about when to flush cpu or mmu updates, we just allow one or > the other to be active. Although there is no real reason a more comprehensive > scheme could not be implemented, there is also no demonstrated need for this > extra complexity. > > Signed-off-by: Zachary Amsden <zach at vmware.com> > > --- a/arch/i386/kernel/process.c Tue Dec 12 13:50:50 2006 -0800 > +++ b/arch/i386/kernel/process.c Tue Dec 12 13:50:53 2006 -0800 > @@ -665,6 +665,37 @@ struct task_struct fastcall * __switch_t > load_TLS(next, cpu); > > /* > + * Restore IOPL if needed. > + */ > + if (unlikely(prev->iopl != next->iopl)) > + set_iopl_mask(next->iopl); Small sidenote that this bit undoes a recent change from Chuck Ebbert, which killed iopl_mask update via hypervisor. thanks, -chris
