[PATCH] hvc_console polling mode timer backoff

[Will Schmidt]

On Fri, 2007-13-04 at 17:47 +1000, Michael Ellerman wrote:
> Because this is a super tight performance critical inner loop I've
> changed it to use a shift instead of divide. So now it's more like 1.5%,
> but still the point is it increases faster as time passes.

Using a shift here is a good idea.  I had considered accelerating the
backoff value, but it got more complex than I wanted quickly.. I didnt
consider a shift. :-) 

> It'd be good if some more people can bang on this and see what they
> think of the interactivity.

Still works OK on my power4.   I can see the delay on my console, but
I'm specifically looking for it, I don't think it's an issue. 

> +#include <linux/debugfs.h>
> +static int hvc_debug_init(void)
> +{
> +	debugfs_create_u32("hvc_timeout", 0400, NULL, &timeout);
> +	return 0;
> +}
> +__initcall(hvc_debug_init);
> +

Is this part temporary for your graphing, or think it's something that
should go in? 
I used /proc/timer_stats output for my graphing, just dont have a good
public spot to upload the pics.. 

-will