* Zachary Amsden ([email protected]) 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 <[email protected]>
>
> --- 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
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