Re: 2.6.17-rc5-mm1

[Martin Bligh <mbligh@google.com>]

Ingo Molnar wrote:
> * Martin Bligh <mbligh@google.com> 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.