Re: [PATCH] genirq: Add default affinity mask command line option

Hi Francesco,

Thanks for your comments on the patch.

On 18/11/12 10:41, Francesco Lavra wrote:

Hi,

On 11/12/2012 05:57 PM, Punit Agrawal wrote:

...

I am attaching a patch by Thomas Gleixner which adds a kernel command line parameter to set the defauilt IRQ affinity mask. Could you please integrate this in your tree for the next Linaro release?

I've been using this patch for sometime now and it doesn't introduce any regressions. There is a possibility that this patch will make it upstream via the RT patches in the near future but in the meanwhile, we'd like to carry this patch as well.

Cheers, Punit

From 52a7d44f58a262e166575abc57aa0bd3bfc8cfbb Mon Sep 17 00:00:00 2001 From: Thomas Gleixner tglx@linutronix.de Date: Fri, 25 May 2012 16:59:47 +0200 Subject: [PATCH] genirq: Add default affinity mask command line option

If we isolate CPUs, then we don't want random device interrupts on them. Even w/o the user space irq balancer enabled we can end up with irqs on non boot cpus.

Allow to restrict the default irq affinity mask.

Signed-off-by: Thomas Gleixner tglx@linutronix.de

Documentation/kernel-parameters.txt | 9 +++++++++ kernel/irq/irqdesc.c | 21 +++++++++++++++++++-- 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 7d82468..00fedab 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -1164,6 +1164,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted. See comment before ip2_setup() in drivers/char/ip2/ip2base.c.

• irqaffinity= [SMP] Set the default irq affinity mask

•                Format:
  

•                <cpu number>,...,<cpu number>
  

•                or
  

•                <cpu number>-<cpu number>
  

•                (must be a positive range in ascending order)
  

•                or a mixture
  

•                <cpu number>,...,<cpu number>-<cpu number>
  

• irqfixup [HW] When an interrupt is not handled search all handlers for it. Intended to get systems with badly broken

diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c index 192a302..473b2b6 100644 --- a/kernel/irq/irqdesc.c +++ b/kernel/irq/irqdesc.c @@ -23,10 +23,27 @@ static struct lock_class_key irq_desc_lock_class;

#if defined(CONFIG_SMP) +static int __init irq_affinity_setup(char *str) +{

• zalloc_cpumask_var(&irq_default_affinity, GFP_NOWAIT);
• cpulist_parse(str, irq_default_affinity);

Since cpulist_parse() sets all the bits of its cpumask argument, it's not necessary to initialize them to zero during allocation, so I would use alloc_cpumask_var() instead of zalloc_cpumask_var().

...

• /*

• * Set at least the boot cpu. We don't want to end up with
  

• * bugreports caused by random comandline masks
  

• */
  

• cpumask_set_cpu(smp_processor_id(), irq_default_affinity);
• return 1;

+} +__setup("irqaffinity=", irq_affinity_setup);

• static void __init init_irq_default_affinity(void) {

• alloc_cpumask_var(&irq_default_affinity, GFP_NOWAIT);
• cpumask_setall(irq_default_affinity);

+#ifdef CONFIG_CPUMASK_OFFSTACK

• if (!irq_default_affinity)

•        zalloc_cpumask_var(&irq_default_affinity, GFP_NOWAIT);
  

+#endif

The #ifdefery is not necessary here, because if CONFIG_CPUMASK_OFFSTACK is not defined irq_default_affinity cannot be NULL.

The patch was picked up as-is from the RT patches as it implements a functionality that we wanted to better control IRQ affinity. Being part of the RT patches, I hope that it'll merge into mainline via that route and I am not going to try to mainline it. So your comments will be best addressed to the original patch postings on the lkml (Search for RT patches).

If you think it is really important to address your comments for the patch that goes into Linaro kernel, I could address them and send an updated patch. Though in that case, I am not quite sure how to attribute the original author who wrote the patch.

Thanks, Punit

-- Francesco

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