linux-kernel - Re: [RFC/PATCH 3/4] genirq: system set irq affinities

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Date:	Wed, 27 Feb 2008 16:10:33 -0800
From:	Max Krasnyanskiy <maxk@...lcomm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Oleg Nesterov <oleg@...sign.ru>,
	Steven Rostedt <rostedt@...dmis.org>,
	Paul Jackson <pj@....com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC/PATCH 3/4] genirq: system set irq affinities

Besides the notifier stuff it's identical to my genirq patch that I sent to 
Thomas and you for the review ~5 days ago.
There are a couple of things you missed.
Current call site for select_smp_affinity() inside request_irq() is incorrect. 
It ends up moving irq each time requires_irq() is called, and it is called 
multiple times for the shared irqs. My patch moves it into setup_irq() under 
if(!shared) check.

Also the following part is unsafe

> +#ifdef CONFIG_CPUSETS
> +static int system_irq_notifier(struct notifier_block *nb,
> +		unsigned long action, void *cpus)
> +{
> +	cpumask_t *new_system_map = (cpumask_t *)cpus;
> +	int i;
> +
> +	for (i = 0; i < NR_IRQS; i++) {
> +		struct irq_desc *desc = &irq_desc[i];
> +
> +		if (desc->chip == &no_irq_chip || !irq_can_set_affinity(i))
> +			continue;
> +
> +		if (cpus_match_system(desc->affinity)) {
> +			cpumask_t online_system;
> +
> +			cpus_and(online_system, new_system_map, cpu_online_map);
> +
> +			set_balance_irq_affinity(i, online_system);
> +
> +			desc->affinity = online_system;
> +			desc->chip->set_affinity(i, online_system);
Two lines above should be
	irq_set_affinity(i, online_system);

If you look at how irq_set_affinity() is implemented, you'll see this

#ifdef CONFIG_GENERIC_PENDING_IRQ
         set_pending_irq(irq, cpumask);
#else
         desc->affinity = cpumask;
         desc->chip->set_affinity(irq, cpumask);
#endif

set_pending_irq() is the safe way to move pending irqs.

btw It should be ok to call chip->set_affinity() directly from 
select_smp_affinity() because in my patch is is guarantied to be called only 
for the first handler registration.

Max
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