Re: [Qemu-devel] [patch v4 12/16] e1000: apply fine lock on e1000

[Avi Kivity]

On 10/25/2012 06:41 PM, Jan Kiszka wrote:
> On 2012-10-25 18:23, Avi Kivity wrote:
>> On 10/25/2012 03:34 PM, Jan Kiszka wrote:
>> 
>>>>> Second, it clearly shows that we need to address lock-less IRQ delivery.
>>>>> Almost nothing is won if we have to take the global lock again to push
>>>>> an IRQ event to the guest. I'm repeating myself, but the problem to be
>>>>> solved here is almost identical to fast IRQ delivery for assigned
>>>>> devices (which we only address pretty ad-hoc for PCI so far).
>>>>>
>>>> Interesting, could you show me more detail about it, so I can google...
>>>
>>> No need to look that far, just grep for pci_device_route_intx_to_irq,
>>> pci_device_set_intx_routing_notifier and related functions in the code.
>> 
>> We can address it in the same way the memory core supports concurrency,
>> by copying dispatch information into rcu or lock protected data structures.
>> 
>> But I really hope we can avoid doing it now.
> 
> I doubt so as the alternative is taking the BQL while (still) holding
> the device lock. 

Sorry, doesn't parse.

> But that creates ABBA risks.


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