linux-kernel - Re: [RFC 1/4] CONFIG

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Date:	Fri, 20 Jul 2007 07:34:10 -0400
From:	Chris Snook <csnook@...hat.com>
To:	Satyam Sharma <satyam.sharma@...il.com>
CC:	"clameter@....com" <clameter@....com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	akpm@...ux-foundation.org
Subject: Re: [RFC 1/4] CONFIG_STABLE: Define it

Satyam Sharma wrote:
> On 7/20/07, Chris Snook <csnook@...hat.com> wrote:
>> Satyam Sharma wrote:
>> > [ Just cleaning up my inbox, and stumbled across this thread ... ]
>> >
>> >
>> > On 5/31/07, clameter@....com <clameter@....com> wrote:
>> >> Introduce CONFIG_STABLE to control checks only useful for development.
>> >>
>> >> Signed-off-by: Christoph Lameter <clameter@....com>
>> >> [...]
>> >>  menu "General setup"
>> >>
>> >> +config STABLE
>> >> +       bool "Stable kernel"
>> >> +       help
>> >> +         If the kernel is configured to be a stable kernel then 
>> various
>> >> +         checks that are only of interest to kernel development 
>> will be
>> >> +         omitted.
>> >> +
>> >
>> >
>> > "A programmer who uses assertions during testing and turns them off
>> > during production is like a sailor who wears a life vest while drilling
>> > on shore and takes it off at sea."
>> >                                                - Tony Hoare
>> >
>> >
>> > Probably you meant to turn off debug _output_ (and not _checks_)
>> > with this config option? But we already have CONFIG_FOO_DEBUG_BAR
>> > for those situations ...
>>
>> There are plenty of validation and debugging features in the kernel 
>> that go WAY
>> beyond mere assertions, often imposing significant overhead 
>> (particularly when
>> you scale up) or creating interfaces you'd never use unless you were 
>> doing
>> kernel development work.  You really do want these features completely 
>> removed
>> from production kernels.
> 
> As for entire such "development/debugging-related features", most (all, 
> really)
> should anyway have their own config options.

They do.  With kconfig dependencies, we can ensure that those config options are 
off when CONFIG_STABLE is set.  That way you only have to set one option to 
ensure that all these expensive checks are disabled.

>> The point of this is not to remove one-line WARN_ON and BUG_ON checks 
>> (though we
>> might remove a few from fast paths), but rather to disable big chunks of
>> debugging code that don't implement anything visible to a production 
>> workload.
> 
> Oh yes, but it's still not clear to me why or how a kernel-wide 
> "CONFIG_STABLE"
> or "CONFIG_RELEASE" would help ... what's wrong with finer granularity
> "CONFIG_xxx_DEBUG_xxx" kind of knobs?

With kconfig dependencies, we can keep the fine granularity, but not have to 
spend a half hour digging through the configuration to make sure we have a 
production-suitable kernel.

	-- Chris
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