linux-kernel - Re: [PATCH v4.4-rc8 v3] dmaengine: ioatdma: Squelch framesize warnings

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Date:	Fri, 8 Jan 2016 19:58:47 +0000
From:	"Jiang, Dave" <dave.jiang@...el.com>
To:	"Williams, Dan J" <dan.j.williams@...el.com>,
	"tim.gardner@...onical.com" <tim.gardner@...onical.com>
CC:	"dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"der.herr@...r.at" <der.herr@...r.at>,
	"Koul, Vinod" <vinod.koul@...el.com>,
	"prarit@...hat.com" <prarit@...hat.com>,
	"jarkko.nikula@...ux.intel.com" <jarkko.nikula@...ux.intel.com>
Subject: Re: [PATCH v4.4-rc8 v3] dmaengine: ioatdma: Squelch framesize
 warnings

On Fri, 2016-01-08 at 19:41 +0000, Williams, Dan J wrote:
> On Fri, Jan 8, 2016 at 11:25 AM,  <tim.gardner@...onical.com> wrote:
> > From: Tim Gardner <tim.gardner@...onical.com>
> > 
> >   CC [M]  drivers/dma/ioat/prep.o
> > drivers/dma/ioat/prep.c: In function 'ioat_prep_pqxor':
> > drivers/dma/ioat/prep.c:682:1: warning: the frame size of 1048
> > bytes is larger than 1024 bytes [-Wframe-larger-than=]
> >  }
> >  ^
> > drivers/dma/ioat/prep.c: In function 'ioat_prep_pqxor_val':
> > drivers/dma/ioat/prep.c:714:1: warning: the frame size of 1048
> > bytes is larger than 1024 bytes [-Wframe-larger-than=]
> >  }
> > 
> > gcc version 5.3.1 20151219 (Ubuntu 5.3.1-4ubuntu1)
> > 
> > Cc: Vinod Koul <vinod.koul@...el.com>
> > Cc: Dan Williams <dan.j.williams@...el.com>
> > Cc: Dave Jiang <dave.jiang@...el.com>
> > Cc: Prarit Bhargava <prarit@...hat.com>
> > Cc: Nicholas Mc Guire <der.herr@...r.at>
> > Cc: Jarkko Nikula <jarkko.nikula@...ux.intel.com>
> > Signed-off-by: Tim Gardner <tim.gardner@...onical.com>
> > ---
> > 
> > v2 - use per CPU static buffers instead of dynamically allocating
> > memory.
> > v3 - Use get_cpu_var/put_cpu_var which implicitly control
> > preeemption. Drop
> >      the wrapper function that no longer serves any purpose.
> > 
> >  drivers/dma/ioat/prep.c | 29 +++++++++++++++++++++++++----
> >  1 file changed, 25 insertions(+), 4 deletions(-)
> 
> Looks good to me... but now that I think about it, why is MAX_SCF set
> to 1024 in the first place?  Certainly it can't be bigger than the
> maximum number of sources in a single operation which is 8 to 16.
> Even md raid can only support up to 256 devices in an array.  So I
> think that contstant is bogus.
> 
> If we set it to 16 we may not even need the percpu change.
> 
> Dave?

You are right. It was an arbitrary number I threw in there to address
sparse warning. It can be reduced. 256 seems reasonable.