linux-kernel - Re: Average number of instructions per line of kernel code

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Message-ID: <Pine.LNX.4.64.0708301212030.14590@pixie.tetracon-eng.net>
Date:	Thu, 30 Aug 2007 12:29:38 -0400 (EDT)
From:	"J. Scott Kasten" <jscottkasten@...oo.com>
To:	Mohamed Bamakhrama <bamakhrama@...il.com>
cc:	linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org
Subject: Re: Average number of instructions per line of kernel code

On Thu, 30 Aug 2007, Mohamed Bamakhrama wrote:
>>> Hi all,
>>> I have a question regarding the average number of assembly
>>> instructions per line of kernel code. I know that this is a difficult
>>> question since it depends on many factors such as the instruction set

Here's a quick answer, not the best, but quick.

I took a user space flash memory driver I'm doing at work and compiled it 
on my R5000 at home using gcc 4.1 and the MIPS3 abi, stopping with a .o 
file.  I also ran the source through cpp and a couple of grep passes to 
strip out junk that wasn't really code.  This driver may be somewhat 
typical of what you would run into as it has quite a few inline functions 
and such.

The driver.o was about 23000 bytes.  Forgetting about the symboltables and 
just dividing by 4 to estimate instructions and dividing by about 1650 
net lines of code, I got about 3.5 instructions per line of C code.

I'm guessing that ball park, you're looking at 3-5 average - 10 seems high 
except in sections with lots and lots of inlines.

Regards,

-S-
-
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