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

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Date:	Fri, 19 Sep 2014 15:19:46 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	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 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.

-Scott


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