Re: [RFC 1/4] CONFIG_STABLE: Define it

[Chris Snook <csnook@redhat.com>]

Satyam Sharma wrote:
> On 7/20/07, Chris Snook <csnook@redhat.com> wrote:
> > Satyam Sharma wrote:
> > > [ Just cleaning up my inbox, and stumbled across this thread ... ]
> > >
> > >
> > > On 5/31/07, clameter@sgi.com <clameter@sgi.com> wrote:
> > >> Introduce CONFIG_STABLE to control checks only useful for development.
> > >>
> > >> Signed-off-by: Christoph Lameter <clameter@sgi.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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