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

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Date:	Mon, 22 Sep 2014 18:50:40 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	Laurentiu Tudor <b10716@...escale.com>
CC:	Michael Neuling <mikey@...ling.org>, <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 Mon, 2014-09-22 at 11:26 +0300, Laurentiu Tudor wrote:
> 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.

Yes, please resend it once Michael's patch gets merged.

-Scott


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