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

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Date:	Mon, 22 Sep 2014 11:26:26 +0300
From:	Laurentiu Tudor <b10716@...escale.com>
To:	Scott Wood <scottwood@...escale.com>,
	Michael Neuling <mikey@...ling.org>
CC:	<greg@...ah.com>, <arnd@...db.de>, <mpe@...erman.id.au>,
	<benh@...nel.crashing.org>, <cbe-oss-dev@...ts.ozlabs.org>,
	<imunsie@...ibm.com>, <linux-kernel@...r.kernel.org>,
	<linuxppc-dev@...abs.org>, <jk@...abs.org>, <anton@...ba.org>,
	"Laurentiu Tudor" <Laurentiu.Tudor@...escale.com>
Subject: Re: [PATCH 03/15] powerpc/msi: Improve IRQ bitmap allocator

On 09/19/2014 11:19 PM, Scott Wood wrote:
> On Fri, 2014-09-19 at 15:16 -0500, Scott Wood wrote:
>> On Thu, 2014-09-18 at 18:26 +1000, Michael Neuling wrote:
>>> From: Ian Munsie <imunsie@....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@....ibm.com>
>>> Signed-off-by: Michael Neuling <mikey@...ling.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.
> 
> Given the problems with Laurentiu's patch, perhaps it'd be best for me
> to just revert that patch in my tree, and respin it after this patchset
> has been merged.

Let me know if you want me to rebase my stuff on top of Michael's patch.

---
Best Regards, Laurentiu

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