linux-kernel - Re: [Ksummit-2013-discuss] [ATTEND] [ARM ATTEND] kernel data bloat and how to avoid it

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Date:	Fri, 2 Aug 2013 16:11:03 +0800
From:	Greg KH <greg@...ah.com>
To:	Tony Lindgren <tony@...mide.com>
Cc:	ksummit-2013-discuss@...ts.linuxfoundation.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [Ksummit-2013-discuss] [ATTEND] [ARM ATTEND] kernel data bloat
 and how to avoid it

On Fri, Aug 02, 2013 at 12:53:53AM -0700, Tony Lindgren wrote:
> * Greg KH <greg@...ah.com> [130731 05:39]:
> > On Wed, Jul 31, 2013 at 12:38:03AM -0700, Tony Lindgren wrote:
> > > Hi all,
> > > 
> > > Probably the biggest kernel data bloat issue is in the ARM land, but
> > > it also seems that it's becoming a Linux generic issue too, so I
> > > guess it could be discussed in either context.
> > 
> > Why is it specific to ARM?  What is so unique to ARM that causes it to
> > "bloat"?
> 
> I think it has so far showed up on ARM because of no discoverable busses,
> but chances are it will be more of a generic problem.
> 
> > And what exactly do you mean by "bloat"?
> 
> Stuffing data to kernel that should not be in the kernel at all. Or
> if the data is needed by kernel, there should be only one set of the
> data defined rather than multiple copies of the data built into the
> kernel for each SoC or driver variant.
> 
> > > Basically the data bloat issue is there for the arch code and drivers
> > > and may not show up initially until things have headed the wrong way for
> > > too long.
> > 
> > What do you mean by this?  You seem to be very vague here.
> 
> People are unnecessarily defining registers in kernel for similar devices
> over and over again for each new SoC at the arch level and now more and
> more at the driver level.
> 
> One example of that are device tree based drivers that don't describe
> the actual hardware, but instead have a binding that points to an index
> of defined registers in the driver.

Ok, and exactly how much "larger" does something like this cost as a
real number, and as a percentage of the size of the kernel?

thanks,

greg k-h
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