[Xen-devel] Re: [PATCH 08/13] xen/pvticketlock: disable interrupts while blocking

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

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 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?

    J


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