Re: [PATCH linux-next v2 1/2] irq: Add CPU mask affinity hint

From: Peter P Waskiewicz Jr
Date: Fri Apr 30 2010 - 14:03:58 EST


On Fri, 30 Apr 2010, Thomas Gleixner wrote:

On Fri, 30 Apr 2010, Peter P Waskiewicz Jr wrote:

This patch adds a cpumask affinity hint to the irq_desc
structure, along with a registration function and a read-only
proc entry for each interrupt.

This affinity_hint handle for each interrupt can be used by
underlying drivers that need a better mechanism to control
interrupt affinity. The underlying driver can register a
cpumask for the interrupt, which will allow the driver to
provide the CPU mask for the interrupt to anything that
requests it. The intent is to extend the userspace daemon,
irqbalance, to help hint to it a preferred CPU mask to balance
the interrupt into.

Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@xxxxxxxxx>
---

include/linux/interrupt.h | 13 +++++++++++++
include/linux/irq.h | 1 +
kernel/irq/manage.c | 28 ++++++++++++++++++++++++++++
kernel/irq/proc.c | 33 +++++++++++++++++++++++++++++++++
4 files changed, 75 insertions(+), 0 deletions(-)

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 75f3f00..9c9ea2a 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -209,6 +209,9 @@ extern int irq_set_affinity(unsigned int irq, const struct cpumask *cpumask);
extern int irq_can_set_affinity(unsigned int irq);
extern int irq_select_affinity(unsigned int irq);

+extern int irq_register_affinity_hint(unsigned int irq,
+ const struct cpumask *m);

I think we can do with a single funtion irq_set_affinity_hint() and
let the caller set the pointer to NULL.

Ok, I've been running into some issues. If CONFIG_CPUMASK_OFFSTACK is not set, then cpumask_var_t structs are single-element arrays that cannot be NULL'd out. I'm pretty sure I need to keep the unregister part of the API. Thoughts?

+ raw_spin_lock_irqsave(&desc->lock, flags);
+ if (desc->affinity_hint) {
+ seq_cpumask(m, desc->affinity_hint);

Please make a local copy under desc->mask and do the seq_cpumask()
stuff on the local copy outside of desc->lock

I just looked at the original show_affinity function, and it does not grab desc->lock before copying mask out of desc. Should I follow that model, or should I fix that function to honor desc->lock?

-PJ
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