Re: [Xen-devel] [PATCH] xen/arm: Implement dynamic allocation of irq descriptors

[Vijay Kilari <vijay.kilari@xxxxxxxxx>]

Hi Julien,

On Mon, Feb 23, 2015 at 9:55 PM, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
> On 23/02/15 16:09, Vijay Kilari wrote:
>> On Mon, Feb 23, 2015 at 9:10 PM, Julien Grall <julien.grall@xxxxxxxxxx> 
>> wrote:
>>> Hello Vijay,
>>>
>>> On 23/02/15 13:04, Vijay Kilari wrote:
>>>> On Thu, Feb 19, 2015 at 7:33 PM, Julien Grall <julien.grall@xxxxxxxxxx> 
>>>> wrote:
>>>>> On 19/02/15 07:17, vijay.kilari@xxxxxxxxx wrote:
>>>>>> From: Vijaya Kumar K <Vijaya.Kumar@xxxxxxxxxxxxxxxxxx>
>>>>>>
>>>>>> For arm memory for 1024 irq descriptors are allocated
>>>>>> statically irrespective of number of interrupt supported
>>>>>> by the platform.
>>>>>>
>>>>>> With this patch, irq descriptors are allocated at run time
>>>>>> and managed using red-black tree. Functions to insert, search
>>>>>> and delete irq descriptor are implemented in xen/common/irq.c.
>>>>>
>>>>> I think we may want to allocate SPIs/SGIs/PPIs at boot time. This number
>>>>> will never change. We can avoid to always to allocate 1024 IRQs by using
>>>>> the number provided by the GIC.
>>>>
>>>> The irq descriptor is allocated when platform_get_irq() is called or
>>>> route_irq_to_guest()
>>>> only. So we are not allocating based on GIC.
>>>
>>> You didn't understand what I said... I was suggesting to allocate SPIs
>>> at boot time. Using an array for them allow us to access to IRQ desc in
>>> constant time. This may help interrupt latency.
>>
>> Yes, I have thought about it. May be we can choose this approach for SPIs
>> but for LPI's, the GIC can support upto ~32K. So in this case it won't make
>> sense for LPI's
>
> Again... I never said it was a bad idea for LPIs. I was only point out
> that it may not be worth for SPIs.
>
> [..]
>
>>> I think we should consider to create a separate structure for LPI's.
>>
>> Yes, I have created separate structure for LPI's for ITS driver.
>>  But as I said LPI's are to many, so cannot allocate at domain creation.
>
> Ditto. The new structure can be a radix tree. I never suggested to use
> an array.

Thanks for your suggestions. Are u refering to Radix or rb tree?

Regards
Vijay

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