Re: [RFC PATCH 02/16] sched: Introduce CONFIG_SCHED_ENERGY

[Henrik Austad <henrik@austad.us>]

On Tue, Jun 10, 2014 at 12:23:53PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 10, 2014 at 11:06:41AM +0100, Morten Rasmussen wrote:
> > How would you like to disable the energy stuff for users for whom
> > latency is everything?
> > 
> > I mean, we are adding some extra load/utilization tracking. While I
> > think we should do everything possible to minimize the overhead, I think
> > it is unrealistic to assume that it will be zero. Is a some extra 'if
> > (energy_enabled)' acceptable?
> > 
> > I'm open for other suggestions.
> 
> We have the jump-label stuff to do self modifying code ;-) The only
> thing we need to be careful with is data-layout.

Isn't this asking for trouble?

I do get the point of not introducing more make-ifdeffery, but I'm not
so sure the alternative is much better. Do we really want to spend time
tracing down bugs introduced via a self-modifying process in something
as central as the scheduler?

> So I'm _hoping_ we can do all this without more CONFIG knobs, because
> {PREEMPT*SMP*CGROUP^3*NUMA^2} is already entirely annoying to
> build and run test, not to mention that distro builds will have no other
> option than to enable everything anyhow.

True, but if that is the argument, how is adding this as a dynamic thing
any better, you still end up with a test-matrix of the same size?

Building a kernel isn't _that_ much work and it would make the
test-scripts all the much simpler to maintain if we don't have to rely
on some dynamic tweaking of the core.

Just sayin'

-- 
Henrik Austad