[PATCH v2 04/17] powerpc/msi: Improve IRQ bitmap allocator
mpe at ellerman.id.au
Wed Oct 1 17:13:31 EST 2014
On Tue, 2014-30-09 at 10:34:53 UTC, Michael Neuling wrote:
> From: Ian Munsie <imunsie at 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
^ one space after a period, or die!
> 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
What is an AFU directed accelerator?
> 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.
The crucial detail you failed to mention is that you maintain the behaviour that
allocations are naturally aligned.
Can you add a check in the test code at the bottom of the file to confirm that
> diff --git a/arch/powerpc/sysdev/msi_bitmap.c b/arch/powerpc/sysdev/msi_bitmap.c
> index 2ff6302..961a358 100644
> --- a/arch/powerpc/sysdev/msi_bitmap.c
> +++ b/arch/powerpc/sysdev/msi_bitmap.c
> @@ -20,32 +20,37 @@ int msi_bitmap_alloc_hwirqs(struct msi_bitmap *bmp, int num)
> int offset, order = get_count_order(num);
> spin_lock_irqsave(&bmp->lock, flags);
> - /*
> - * 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;
Can we get a newline here :)
> + 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);
This print out is a bit confusing now, should probably just drop the order.
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