Re: [RFC PATCH 3/4] KVM: x86: Add EOI exit bitmap inference

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2015-05-13 11:24, Paolo Bonzini wrote:
> 
> 
> On 13/05/2015 10:10, Jan Kiszka wrote:
>>>>>> There can even be multiple IOAPICs (thanks to your patches overcoming
>>>>>> the single in-kernel instance).
>>>>
>>>> With multiple IOAPICs you have more than 24 GSIs per IOAPIC.  That means
>> I don't think that the number of pins per IOAPIC increases. At least not
>> in the devices I've seen so far.
> 
> Sorry, that was supposed to be "more than 24 GSIs for the IOAPICs".
> 
>>>> that the above loop is broken for multiple IOAPICs.
>> The worst case remains #IOAPIC * 24 iterations - if we have means to
>> stop after the IOAPIC entries, not iterating over all routes.
> 
> Yes.  Which is not too bad if VCPUs can process it in parallel.
> 
>>>> But perhaps when enabling KVM_SPLIT_IRQCHIP we can use args[0] to pass
>>>> the number of IOAPIC routes that will cause EOI exits?
>> And you need to ensure that their routes can be found in the table
>> directly. Given IOAPIC hotplug, that may not be the first ones there...
> 
> Can you reserve a bunch of GSIs at the beginning of the GSI space, and
> use rt->map[] to access them and build the EOI exit bitmap?

Ideally, userspace could give the kernel a hint where to look. It has a
copy of the routing table and manages it, no?

Jan

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