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

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Date:	Thu, 18 Sep 2008 12:19:57 -0400
From:	Jason Baron <jbaron@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/6] loglevel=pci:8,acpi:8,apic=8 support v6

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

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