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

[Jan Kiszka]

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. But that creates ABBA risks.

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
Corporate Competence Center Embedded Linux