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SubjectRe: [tip:irq/core] genirq: Make nr_irqs runtime expandable
On 02/21/2011 07:56 AM, Lars-Peter Clausen wrote:
> On 02/19/2011 08:07 PM, Yinghai Lu wrote:
...

>> [PATCH] genirq: use IRQ_BITMAP_BITS as search size
>>
>> instead of nr_irqs.
>>
>> Otherwise bitmap_find_next_area could exit with larger start and in extreme
>> case we could fail to get wrong irqs return.
>>
>> For example:
>> IRQ_BITMAP_BITS=10240
>> nr_irqs=8192
>> cnt=2048
>>
>> and bit 0 to bit 8190 are set already.
>>
>> before patch start from bit_find_next_area() will be 8191+2048.
>> later irq_expand_nr_irqs will set nr_irqs 10240.
>> finally irq_alloc_descs will return [8191+2048, 8191+2048+2047] happily..
>>
>> with this patch, will get correct [8191, 8191+2047]
>>
>> Signed-off-by: Yinghai Lu <yinghai@kernel.org>
>>
>> ---
>> kernel/irq/irqdesc.c | 5 +++--
>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> Index: linux-2.6/kernel/irq/irqdesc.c
>> ===================================================================
>> --- linux-2.6.orig/kernel/irq/irqdesc.c
>> +++ linux-2.6/kernel/irq/irqdesc.c
>> @@ -346,12 +346,13 @@ irq_alloc_descs(int irq, unsigned int fr
>>
>> mutex_lock(&sparse_irq_lock);
>>
>> - start = bitmap_find_next_zero_area(allocated_irqs, nr_irqs, from, cnt, 0);
>> + start = bitmap_find_next_zero_area(allocated_irqs, IRQ_BITMAP_BITS,
>> + from, cnt, 0);
>> ret = -EEXIST;
>> if (irq >=0 && start != irq)
>> goto err;
>>
>> - if (start >= nr_irqs) {
>> + if (start + cnt > nr_irqs) {
>> ret = irq_expand_nr_irqs(cnt);
> Just a minor thing, but if there are still unused irqs available at the end of
> the current range, you'll end up expanding the range more then you need to.
> So either do
> irq_expand_nr_irqs(nr_irqs - start + cnt);
> or change irq_expand_nr_irqs to let it take the new total number of irqs.

yes. please check second way that you suggested.

[PATCH -v2] genirq: use IRQ_BITMAP_BITS as search size

Otherwise bitmap_find_next_area could exit with larger start and in extreme
case we could fail to get wrong irqs return.

For example:
IRQ_BITMAP_BITS=10240
nr_irqs=8192
cnt=2048

and bit 0 to bit 8190 are set already.

before patch start from bit_find_next_area() will be 8191+2048.
later irq_expand_nr_irqs will set nr_irqs 10240.
finally irq_alloc_descs will return [8191+2048, 8191+2048+2047] happily..

with this patch, will get correct [8191, 8191+2047]

-v2: let irq_expand_nr_irqs take new nr_irqs instead of cnt, so do not
increase nr_irqs too much extra.
Suggested by "Lars-Peter" Clausen <lars@metafoo.de>

Signed-off-by: Yinghai Lu <yinghai@kernel.org>

---
kernel/irq/irqdesc.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)
Index: linux-2.6/kernel/irq/irqdesc.c
===================================================================
--- linux-2.6.orig/kernel/irq/irqdesc.c
+++ linux-2.6/kernel/irq/irqdesc.c
@@ -207,11 +207,11 @@ struct irq_desc * __ref irq_to_desc_allo
return NULL;
}

-static int irq_expand_nr_irqs(unsigned int cnt)
+static int irq_expand_nr_irqs(int new_nr_irqs)
{
- if (nr_irqs + cnt > IRQ_BITMAP_BITS)
+ if (new_nr_irqs > IRQ_BITMAP_BITS)
return -ENOMEM;
- nr_irqs += cnt;
+ nr_irqs = new_nr_irqs;
return 0;
}

@@ -298,7 +298,7 @@ static inline int alloc_descs(unsigned i
return start;
}

-static int irq_expand_nr_irqs(unsigned int cnt)
+static int irq_expand_nr_irqs(int new_nr_irqs)
{
return -ENOMEM;
}
@@ -346,13 +346,14 @@ irq_alloc_descs(int irq, unsigned int fr

mutex_lock(&sparse_irq_lock);

- start = bitmap_find_next_zero_area(allocated_irqs, nr_irqs, from, cnt, 0);
+ start = bitmap_find_next_zero_area(allocated_irqs, IRQ_BITMAP_BITS,
+ from, cnt, 0);
ret = -EEXIST;
if (irq >=0 && start != irq)
goto err;

- if (start >= nr_irqs) {
- ret = irq_expand_nr_irqs(cnt);
+ if (start + cnt > nr_irqs) {
+ ret = irq_expand_nr_irqs(start + cnt);
if (ret)
goto err;
}

>
> Btw., with this patch in place does it make sense to initialize nr_irqs to
> anything else then initcnt in early_irq_init?

i have one for x86 and it will set nr_irqs to nr_irqs_gsi

[PATCH] x86, irq: keep nr_irqs as low as possible

For sparseirq, We can expand nr_irqs later if needed, so could
keep it from small for beginning.

Assign it to minium value of vectors of all cpus and gsi pins


Signed-off-by: Yinghai Lu <yinghai@kernel.org>

---
arch/x86/kernel/apic/io_apic.c | 13 ++++---------
1 file changed, 4 insertions(+), 9 deletions(-)
Index: linux-2.6/arch/x86/kernel/apic/io_apic.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/apic/io_apic.c
+++ linux-2.6/arch/x86/kernel/apic/io_apic.c
@@ -3642,16 +3642,11 @@ int __init arch_probe_nr_irqs(void)
{
int nr;

- if (nr_irqs > (NR_VECTORS * nr_cpu_ids))
- nr_irqs = NR_VECTORS * nr_cpu_ids;
+ nr = NR_VECTORS * nr_cpu_ids;
+ if (nr < nr_irqs)
+ nr_irqs = nr;

- nr = nr_irqs_gsi + 8 * nr_cpu_ids;
-#if defined(CONFIG_PCI_MSI) || defined(CONFIG_HT_IRQ)
- /*
- * for MSI and HT dyn irq
- */
- nr += nr_irqs_gsi * 16;
-#endif
+ nr = nr_irqs_gsi;
if (nr < nr_irqs)
nr_irqs = nr;



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