Messages in this thread | | | From | Michael Ellerman <> | Subject | Re: [PATCH v2 04/17] powerpc/msi: Improve IRQ bitmap allocator | Date | Wed, 1 Oct 2014 17:13:31 +1000 (EST) |
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On Tue, 2014-30-09 at 10:34:53 UTC, Michael Neuling wrote: > From: Ian Munsie <imunsie@au1.ibm.com> > > 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?
> 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
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