Re: [PATCH v2 04/17] powerpc/msi: Improve IRQ bitmap allocator
From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2014-10-01 07:13:34
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On Tue, 2014-30-09 at 10:34:53 UTC, Michael Neuling wrote:
From: Ian Munsie <redacted> Currently msi_bitmap_alloc_hwirqs() will round up any IRQ allocation requests
request
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
context
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
x
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 please?
quoted hunk ↗ jump to hunk
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. cheers