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

Scott Wood
2014-09-19T20:16:34Z

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.

-Scott

> 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)
> {