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    SubjectRe: [PATCH 5/5] xen: events: use per-cpu variable for cpu_evtchn_mask
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    On Tue, 2010-10-26 at 15:36 +0100, Konrad Rzeszutek Wilk wrote:
    > On Mon, Oct 25, 2010 at 05:23:33PM +0100, Ian Campbell wrote:
    > > I can't see any reason why it isn't already.
    > >
    > > Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
    > > ---
    > > drivers/xen/events.c | 31 +++++++++++--------------------
    > > 1 files changed, 11 insertions(+), 20 deletions(-)
    > >
    > > diff --git a/drivers/xen/events.c b/drivers/xen/events.c
    > > index 9b58505..144ff72 100644
    > > --- a/drivers/xen/events.c
    > > +++ b/drivers/xen/events.c
    > > @@ -110,19 +110,9 @@ static int *pirq_to_irq;
    > > static int nr_pirqs;
    > >
    > > static int *evtchn_to_irq;
    > > -struct cpu_evtchn_s {
    > > - unsigned long bits[NR_EVENT_CHANNELS/BITS_PER_LONG];
    > > -};
    > >
    > > -static __initdata struct cpu_evtchn_s init_evtchn_mask = {
    > > - .bits[0 ... (NR_EVENT_CHANNELS/BITS_PER_LONG)-1] = ~0ul,
    > > -};
    > > -static struct cpu_evtchn_s *cpu_evtchn_mask_p = &init_evtchn_mask;
    > > -
    > > -static inline unsigned long *cpu_evtchn_mask(int cpu)
    > > -{
    > > - return cpu_evtchn_mask_p[cpu].bits;
    > > -}
    > > +static DEFINE_PER_CPU(unsigned long [NR_EVENT_CHANNELS/BITS_PER_LONG],
    > > + cpu_evtchn_mask);
    > >
    > > /* Xen will never allocate port zero for any purpose. */
    > > #define VALID_EVTCHN(chn) ((chn) != 0)
    > > @@ -301,7 +291,7 @@ static inline unsigned long active_evtchns(unsigned int cpu,
    > > unsigned int idx)
    > > {
    > > return (sh->evtchn_pending[idx] &
    > > - cpu_evtchn_mask(cpu)[idx] &
    > > + per_cpu(cpu_evtchn_mask, cpu)[idx] &
    > > ~sh->evtchn_mask[idx]);
    > > }
    > >
    > > @@ -314,8 +304,8 @@ static void bind_evtchn_to_cpu(unsigned int chn, unsigned int cpu)
    > > cpumask_copy(irq_to_desc(irq)->affinity, cpumask_of(cpu));
    > > #endif
    > >
    > > - __clear_bit(chn, cpu_evtchn_mask(cpu_from_irq(irq)));
    > > - __set_bit(chn, cpu_evtchn_mask(cpu));
    > > + __clear_bit(chn, per_cpu(cpu_evtchn_mask, cpu_from_irq(irq)));
    > > + __set_bit(chn, per_cpu(cpu_evtchn_mask, cpu));
    > >
    > > info_for_irq(irq)->cpu = cpu;
    > > }
    > > @@ -332,7 +322,11 @@ static void init_evtchn_cpu_bindings(void)
    > > }
    > > #endif
    > >
    > > - memset(cpu_evtchn_mask(0), ~0, sizeof(struct cpu_evtchn_s));
    > > + printk(KERN_CRIT "%s: CPU0 at %p size %zd\n", __func__,
    >
    > If this is per_cpu, wouldn't the comment 'CPU0 at' be improper?

    Oops, that was just debug anyway.

    > Hmm, so we use percpu structure, but all of the event channel and such
    > are set for CPU0. So what is the benefit of this, when the interrupts
    > are _only_ happening on CPU0?

    All event channels start off bound to VCPU0 so we need to initialise
    cpu_evtchn_mask(0) to have all ones and leave all the other CPU's
    bitmaps with all zeros.

    > Oh, right, there is also the rebind cpu function somewhere so that the
    > spinlock, timers, etc are allocated on other CPUs, right?

    All evtchn's start off bound to VCPU 0 but the kernel can rebind as
    necessary.

    Ian.



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