Re: [Xen-devel] [PATCH-4.5 3/4] xen/arm: do not request maintenance_interrupts

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 02/10/2014 05:06 PM, Stefano Stabellini wrote:
> On Fri, 7 Feb 2014, Julien Grall wrote:
>> On 07/02/14 18:56, Stefano Stabellini wrote:
>>    > +static void gic_clear_lrs(struct vcpu *v)
>>> +{
>>> +    struct pending_irq *p;
>>> +    int i = 0, irq;
>>> +    uint32_t lr;
>>> +    bool_t inflight;
>>> +
>>> +    ASSERT(!local_irq_is_enabled());
>>> +
>>> +    while ((i = find_next_bit((const long unsigned int *)
>>> &this_cpu(lr_mask),
>>> +                              nr_lrs, i)) < nr_lrs) {
>>
>> Did you look at to ELRSR{0,1} registers which list the usable LRs? I think 
>> you
>> can use it with the this_cpu(lr_mask) to avoid browsing every LRs.
> 
> Given that we only have 4 LR registers, I think that unconditionally
> reading 2 ELRSR registers would cost more than simply checking lr_mask
> on average.

The maximum number of LR registers is 64. I agree that the current
hardwares only handle 4 ... but we should think about future hardware.

-- 
Julien Grall

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