linux-kernel - Re: [PATCH -mm 1/5] Blackfin: blackfin architecture patch update

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Message-Id: <200703050826.56966.rgetz@blackfin.uclinux.org>
Date:	Mon, 5 Mar 2007 08:26:56 -0500
From:	Robin Getz <rgetz@...ckfin.uclinux.org>
To:	"Paul Mundt" <lethal@...ux-sh.org>
Cc:	"Bernd Schmidt" <bernds_cb1@...nline.de>,
	"Wu, Bryan" <bryan.wu@...log.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm 1/5] Blackfin: blackfin architecture patch update

On Mon 5 Mar 2007 07:39, Paul Mundt pondered:
> On Mon, Mar 05, 2007 at 01:32:07PM +0100, Bernd Schmidt wrote:
>  > Paul Mundt wrote:
>  > >>+comment "Memory Optimizations"
>  > >>+
>  > >>+config I_ENTRY_L1
>  > >>+   bool "Locate interrupt entry code in L1 Memory"
>  > >>+   default y
>  > >>+   help
>  > >>+     If enabled interrupt entry code (STORE/RESTORE CONTEXT) is
>  > >> linked +     into L1 instruction memory.(less latency)
>  > >>+
>  > >
>  > >Wow, this is really crying out for a special linker section with
>  > > slightly more intelligent relocation logic. You should flag the
>  > > performance critical parts to be located in L1 memory directly with a
>  > > section attribute, rather than making everything selectable. If you
>  > > overflow you can simply spill in to main memory.
>  >
>  > This is done intentionally, because it's also possible for user code to
>  > be loaded into L1 memory.  We want to give users the option to avoid
>  > filling it all up with kernel code.
>
>  So then why not make the userspace component of it optional and allow a
> size cap for kernel usage that's configurable if it's enabled? This degree
> of abstraction is almost worse than no abstraction.

I don't understand why you think lots of options are a bad thing??

For most embedded targets, people want/need easy knobs to turn to try and 
optimise the system level performance. I would guess that SH users want to do 
the same thing?

That is what this does - it is just a easy to use knob.

-Robin
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