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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2014-02-10 at 17:06 +0000, 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.

You also need to actually read the LR and do some bit masking etc don't
you?

What about implementations with >4 LRs?

Ian.


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