linux-kernel - Re: [PATCH 00/25] dyn_array and nr

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Date:	Sun, 3 Aug 2008 01:25:09 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Dhaval Giani" <dhaval@...ux.vnet.ibm.com>,
	"Mike Travis" <travis@....com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/25] dyn_array and nr_irqs support v3

On Sat, Aug 2, 2008 at 11:39 PM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
> "Yinghai Lu" <yhlu.kernel@...il.com> writes:
>
>> On Sat, Aug 2, 2008 at 10:51 PM, Eric W. Biederman
>> <ebiederm@...ssion.com> wrote:
>>>
>>> It appears that quite a few of the places you have changed are testing
>>> to see if an irq is valid.  The idiomatic way to perform that test in
>>> the kernel is:
>>>
>>> if (irq)
>>
>> is uninitialized irq to be -1 or 0?
>
> 0.  There is a long history behind it, but by decree of Linus and to conform
> with reasonable intuition 0 is not a valid irq except in certain arch specific
> corner cases.
>
>>> With no test to see if you are >= NR_IRQS.
>>>
>>> I expect that is the change we want in the drivers that are performing such a
>> silly
>>> extra check.
>>
>> is_irq_valid(irq_no) ?
>>
>> wait to see your new patchset about dyn irq_cfg and irq_desc
>
> I haven't promised one, at least not lately.  I went down a couple of
> blind alleys and figured out what needed to be accomplished and then
> ran out of steam about a year and a half 2 years ago, and I haven't
> been able to get back to it.
>

how about

diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
index f4c8a03..aa6888c 100644
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -47,19 +47,73 @@ handle_bad_irq(unsigned int irq, struct irq_desc *desc)
  *
  * Controller mappings for all interrupt sources:
  */
-struct irq_desc irq_desc[NR_IRQS] __cacheline_aligned_in_smp = {
-       [0 ... NR_IRQS-1] = {
-               .status = IRQ_DISABLED,
-               .chip = &no_irq_chip,
-               .handle_irq = handle_bad_irq,
-               .depth = 1,
-               .lock = __SPIN_LOCK_UNLOCKED(irq_desc->lock),
+static irq_desc **irq_desc_ptr;
+DEFINE_DYN_ARRAY(irq_desc_ptr, sizeof(struct irq_desc *), nr_irqs,
PAGE_SIZE, NULL);
+
+#define NR_IRQ_DESC    4096
+
+static struct irq_desc irq_desc__init = {
+       .irq = -1;
+       .status = IRQ_DISABLED,
+       .chip = &no_irq_chip,
+       .handle_irq = handle_bad_irq,
+       .depth = 1,
+       .lock = __SPIN_LOCK_UNLOCKED(irq_desc->lock),
 #ifdef CONFIG_SMP
-               .affinity = CPU_MASK_ALL
+       .affinity = CPU_MASK_ALL
 #endif
-       }
 };

+static int nr_irq_desc = NR_IRQ_DESC;
+
+static int __init parse_nr_irq_desc(char *arg)
+{
+        if (arg)
+                nr_irq_desc = simple_strtoul(arg, NULL, 0);
+        return 0;
+}
+
+early_param("nr_irq_desc", parse_nr_irq_desc);
+
+static void __init init_work(void *data)
+{
+       struct dyn_array *da = data;
+       int i;
+       struct  irq_desc *desc;
+
+       desc = *da->name;
+
+       for (i = 0; i < *da->nr; i++)
+               memcpy(&desc[i], &irq_desc_init, sizeof(struct irq_desc));
+}
+
+static struct irq_desc *irq_desc;
+DEFINE_DYN_ARRAY(irq_desc, sizeof(struct irq_desc), nr_irq_desc,
PAGE_SIZE, init_work);
+
+struct irq_desc *get_irq_desc(int irq)
+{
+       struct irq_desc *desc;
+       int i;
+
+       desc = irq_desc_ptr[irq];
+
+       if (desc)
+               return desc;
+
+       for (i = 0; i < nr_irq_desc; i++) {
+               if (irq_desc[i]->irq != -1)
+                       continue;
+
+               desc = &irq_desc[i];
+               desc->irq = irq;
+               irq_desc_ptr[irq] = desc;
+
+               return desc;
+       }
+
+       panic("please boot with nr_irq_desc=%d\n", nr_irq_desc * 2);
+}
+
 /*
  * What should we do if we get a hw irq event on an illegal vector?
  * Each architecture has to answer this themself.


and later use get_irq_desc(i) instead irq_desc + i;

YH
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