Re: [PATCH 03/15] powerpc/msi: Improve IRQ bitmap allocator

Laurentiu Tudor
2014-09-22T08:43:24Z

On 09/19/2014 11:16 PM, Scott Wood wrote:
> On Thu, 2014-09-18 at 18:26 +1000, Michael Neuling wrote:
>> From: Ian Munsie <imunsie@au1.ibm.com>
>>
>> Currently msi_bitmap_alloc_hwirqs() will round up any IRQ allocation requests
>> to the nearest power of 2. eg. ask for 5 IRQs and you'll get 8. This wastes a
>> lot of IRQs which can be a scarce resource.
>>
>> For cxl we can require multiple IRQs for every contexts that is attached to the
>> accelerator. For AFU directed accelerators, there may be 1000s of contexts
>> attached, hence we can easily run out of IRQs, especially if we are needlessly
>> wasting them.
>>
>> This changes the msi_bitmap_alloc_hwirqs() to allocate only the required number
>> of IRQs, hence avoiding this wastage.
>>
>> Signed-off-by: Ian Munsie <imunsie@au1.ibm.com>
>> Signed-off-by: Michael Neuling <mikey@neuling.org>
>> ---
>> arch/powerpc/sysdev/msi_bitmap.c | 18 +++++++++++++-----
>> 1 file changed, 13 insertions(+), 5 deletions(-)
>
> This conflicts with (and partially duplicates)
> http://patchwork.ozlabs.org/patch/381892/
> which I have in my tree. How should we handle it?
>
> Laurentiu, from looking at the overlap between patches I see a problem
> with your existing patch, regarding the out-of-irqs path and
> msi_bitmap_free_hwirqs(), so one way or another that needs to get fixed
> soon.
>

Agree. My patch lacks error checking so Michael's patch is better.

---
Best Regards, Laurentiu

>
>> diff --git a/arch/powerpc/sysdev/msi_bitmap.c b/arch/powerpc/sysdev/msi_bitmap.c
>> index 2ff6302..e001559 100644
>> --- a/arch/powerpc/sysdev/msi_bitmap.c
>> +++ b/arch/powerpc/sysdev/msi_bitmap.c
>> @@ -24,28 +24,36 @@ int msi_bitmap_alloc_hwirqs(struct msi_bitmap *bmp, int num)
>> * This is fast, but stricter than we need. We might want to add
>> * a fallback routine which does a linear search with no alignment.
>> */
>> - offset = bitmap_find_free_region(bmp->bitmap, bmp->irq_count, order);
>> + offset = bitmap_find_next_zero_area(bmp->bitmap, bmp->irq_count, 0,
>> + num, (1 << order) - 1);
>> + if (offset > bmp->irq_count)
>> + goto err;
>> + bitmap_set(bmp->bitmap, offset, num);
>> spin_unlock_irqrestore(&bmp->lock, flags);
>>
>> pr_debug("msi_bitmap: allocated 0x%x (2^%d) at offset 0x%x\n",
>> num, order, offset);
>>
>> return offset;
>> +err:
>> + spin_unlock_irqrestore(&bmp->lock, flags);
>> + return -ENOMEM;
>> }
>> +EXPORT_SYMBOL(msi_bitmap_alloc_hwirqs);
>>
>> void msi_bitmap_free_hwirqs(struct msi_bitmap *bmp, unsigned int offset,
>> unsigned int num)
>> {
>> unsigned long flags;
>> - int order = get_count_order(num);
>>
>> - pr_debug("msi_bitmap: freeing 0x%x (2^%d) at offset 0x%x\n",
>> - num, order, offset);
>> + pr_debug("msi_bitmap: freeing 0x%x at offset 0x%x\n",
>> + num, offset);
>>
>> spin_lock_irqsave(&bmp->lock, flags);
>> - bitmap_release_region(bmp->bitmap, offset, order);
>> + bitmap_clear(bmp->bitmap, offset, num);
>> spin_unlock_irqrestore(&bmp->lock, flags);
>> }
>> +EXPORT_SYMBOL(msi_bitmap_free_hwirqs);
>>
>> void msi_bitmap_reserve_hwirq(struct msi_bitmap *bmp, unsigned int hwirq)
>> {
>
>