Re: [PATCH 0/6] loglevel=pci:8,acpi:8,apic=8 support v6

Jason Baron
2008-09-18T16:21:28Z

On Thu, Sep 18, 2008 at 08:57:50AM -0700, H. Peter Anvin wrote:
> Jason Baron wrote:
>>
>> if we take this argument to its extreme, then we end up spending all of
>> our time verifying that the kernel is working correctly and no time
>> actually doing work. I think 'printk_ratelimit' captures this. Thus,
>> the line has to be drawn somewhere. If you want the messages in 'dmesg'
>> use,
>> printk(KERN_DEBUG), and 'grep'. For the rest, I propose pre-filtering, which is
>> what 'dynamic debug' uses.
>>
>
> Taking any argument to its extreme and you come up with something
> ridiculous.
>
> One could equally argue that if you have so many debugging messages that
> you have to prefilter for performance, you're so bloating your kernel
> that you need to stop.

in my testing there was no significant difference between pre-filtering
vs. not built in. However, there was a measureable affect of having them
built in vs. not built in.

>
> I find it highly questionable that it makes sense to put even skipped
> messages into hot paths in the production kernel. Skipped prints are
> NOT free, even if they are lot cheaper than actually rendering the
> string.
>

If you feel that way, you simply don't have to turn the single CONFIG_ on.
Futher, the patchset allows fine-grained control over the modules that
you would want to enable/disable.

thanks,

-Jason