On 09/07/2011 10:09 PM, Jeremy Fitzhardinge wrote:
On 09/07/2011 10:41 AM, Avi Kivity wrote:
>> Hm, I'm interested to know what you're thinking in more detail. Can you
>> leave an NMI pending before you block in the same way you can with
>> "sti;halt" with normal interrupts?
>
>
> Nope. But you can do
>
> if (regs->rip in critical section)
> regs->rip = after_halt;
>
> and effectively emulate it. The critical section is something like
>
> critical_section_start:
> if (woken_up)
> goto critical_section_end;
> hlt
> critical_section_end:
Hm. It's a pity you have to deliver an actual interrupt to implement
the kick though.
I don't think it's that expensive, especially compared to the
double-context-switch and vmexit of the spinner going to sleep. On AMD
we do have to take an extra vmexit (on IRET) though.
>>
>> I was thinking you might want to do something with monitor/mwait to
>> implement the blocking/kick ops. (Handwave)
>>
>
> monitor/mwait are incredibly expensive to virtualize since they
> require write-protecting a page, IPIs flying everywhere and flushing
> tlbs, not to mention my lovely hugepages being broken up mercilessly.
Or what about a futex-like hypercall?
Well we could have a specialized sleep/wakeup hypercall pair like Xen,
but I'd like to avoid it if at all possible.
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