The addition of the generic affinity autoselector has introduced
a regression in SN2 Altix.
In the past, request_irq()'s call to select_smp_affinity() was
essentially a noop.
#ifdef CONFIG_AUTO_IRQ_AFFINITY
extern int select_smp_affinity(unsigned int irq);
#else
static inline int select_smp_affinity(unsigned int irq)
{
return 1;
}
Now changes have created do_irq_select_affinity(), which is
executed by a call to request_irq().
request_irq()
__setup_irq()
do_irq_select_affinity()
do_irq_select_affinity() will call the set_affinity() routine,
with a default mask. On SN2 (and possibly all ia64 platforms),
this will retarget all device interrupts to the same CPU, most
likely CPU0.
#ifndef CONFIG_AUTO_IRQ_AFFINITY
/*
* Generic version of the affinity autoselector.
*/
int do_irq_select_affinity(unsigned int irq, struct irq_desc *desc)
{
cpumask_t mask;
if (!irq_can_set_affinity(irq))
return 0;
cpus_and(mask, cpu_online_map, irq_default_affinity);
/*
* Preserve an userspace affinity setup, but make sure that
* one of the targets is online.
*/
if (desc->status & (IRQ_AFFINITY_SET | IRQ_NO_BALANCING)) {
if (cpus_intersects(desc->affinity, cpu_online_map))
mask = desc->affinity;
else
desc->status &= ~IRQ_AFFINITY_SET;
}
desc->affinity = mask;
desc->chip->set_affinity(irq, mask);
return 0;
}
This set_affinity call undoes all the performance related interrupt
targetting that the SN2 PROM did at boot.
I'm looking at a patch that makes use of the new IRQ_AFFINITY_SET
flag in the irq_desc to get around this.
Is this an issue for all ia64 platforms? Or does irq balancing
factor in here? IRQ balancing is disabled on SN2.
John Keller
--
To unsubscribe from this list: send the line "unsubscribe linux-ia64" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
|