Re: [patch 1/3] move WARN_ON() out of line

[Matt Mackall]

On Thu, 2008-01-03 at 01:56 +0100, Arjan van de Ven wrote:
> Subject: move WARN_ON() out of line
> From: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
> CC: Ingo Molnar <mingo@xxxxxxx>
> CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> 
> A quick grep shows that there are currently 1145 instances of WARN_ON
> in the kernel. Currently, WARN_ON is pretty much entirely inlined,
> which makes it hard to enhance it without growing the size of the kernel
> (and getting Andrew unhappy).
> 
> This patch moves WARN_ON() out of line entirely. I've considered keeping
> the test inline and moving only the slowpath out of line, but I decided
> against that: an out of line test reduces the pressure on the CPUs
> branch predictor logic and gives smaller code, while a function call
> to a fixed location is quite fast. Likewise I've considered doing something
> similar to BUG() (eg use a trapping instruction) but that's not really
> better (it needs the test inline again and recovering from an invalid
> instruction isn't quite fun).
> 
> The code size reduction of this patch was about 6.5Kb (on a distro style
> .config):
> 
>     text	   data	    bss	    dec	    hex	filename
> 3096493	 293455	2760704	6150652	 5dd9fc	vmlinux.before
> 3090006	 293455	2760704	6144165	 5dc0a5	vmlinux.after
> 
> Signed-off-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>

I hate the do_foo naming scheme (how about __warn_on?), but otherwise:

Acked-by: Matt Mackall <mpm@xxxxxxxxxxx>

> +		printk(KERN_WARNING "WARNING: at %s:%d %s()\n",
> +			__FILE__, __LINE__, __FUNCTION__);
> +		dump_stack();

While we're here, I'll mention that dump_stack probably ought to take a
severity level argument.

-- 
Mathematics is the supreme nostalgia of our time.

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