Re: 2.6.17-rc5-mm1

[Martin Bligh]

Ingo Molnar wrote:
> * Martin Bligh <mbligh@xxxxxxxxxx> wrote:
>
>
> > > > OK. So what's the perf impact of the new version on a 32 cpu machine? 
> > > > ;-) Maybe it's fine, maybe it's not.
> > >
> > >
> > > no idea, but it shouldnt be nearly as bad as say SLAB_DEBUG.
> >
> > The "no idea" is hardly reassuring ;-)
> > The latter point is definitely valid though, it's not an isolated issue.
>
>
> > Adding new runs is easy. Changing the harness is hard ;-)
>
>
> ok. How about a CONFIG_DEBUG_NO_OVERHEAD option, that would default to 
> disabled but which you could set to y. Then we could make all the more 
> expensive debug options:
>
> 	default y if !CONFIG_DEBUG_NO_OVERHEAD
>
> this would still mean you'd have to turn off CONFIG_DEBUG_NO_OVERHEAD, 
> but it would be automatically maintainable for you after that initial 
> effort, and we'd be careful to always flag new debugging options with 
> this flag, if they are expensive. And initially i'd define "expensive" 
> as "anything that adds runtime overhead".
>
> would this be acceptable to you?

Sure, makes sense. I don't care which way up it is, ie
CONFIG_DEBUG_OVERHEAD vs CONFIG_DEBUG_NO_OVERHEAD, as long as it's
easily separable.

There's probably other debug stuff we can turn on too, if we do that.

M.
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