From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [103.22.144.67]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 7AAEB1A18EB for ; Wed, 1 Oct 2014 17:13:32 +1000 (EST) In-Reply-To: <1412073306-13812-5-git-send-email-mikey@neuling.org> To: Michael Neuling , greg@kroah.com, arnd@arndb.de, mpe@ellerman.id.au, benh@kernel.crashing.org From: Michael Ellerman Subject: Re: [PATCH v2 04/17] powerpc/msi: Improve IRQ bitmap allocator Message-Id: <20141001071331.CBE1B14017C@ozlabs.org> Date: Wed, 1 Oct 2014 17:13:31 +1000 (EST) Cc: cbe-oss-dev@lists.ozlabs.org, mikey@neuling.org, "Aneesh Kumar K.V" , imunsie@au.ibm.com, linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org, jk@ozlabs.org, anton@samba.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, 2014-30-09 at 10:34:53 UTC, Michael Neuling wrote: > From: Ian Munsie > > 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