Re: [RFC PATCH v2 00/17] Core scheduling v2

[Ingo Molnar <mingo@kernel.org>]

* Mel Gorman <mgorman@techsingularity.net> wrote:

> > Interesting.
> > 
> > Here too I'm wondering whether the scheduler could do something to 
> > improve the saturated case: which *is* an important workload, as kernel 
> > hackers tend to over-load their systems a bit when building kernel, to 
> > make sure the system is at least 100% utilized. ;-)
> > 
> 
> Every so often I try but I never managed to settle on a heuristic that 
> helped this case without breaking others. The biggest hurdle is that 
> typically things are better if migrations are low but it's hard to do 
> that in a way that does not also stack tasks on the same CPUs 
> prematurely.

So instead of using a heuristic (which are fragile and most of them are 
also annoyingly non-deterministic and increase overall noise and make 
measurements harder) I'd suggest using SCHED_BATCH just as a hardcore 
toggle to maximize for CPU-bound throughput.

It's not used very much, but the kernel build could use it by default 
(i.e. we could use a "chrt -b" call within the main Makefile), so it 
would be the perfect guinea pig and wouldn't affect anything else.

I.e. we could use SCHED_BATCH to maximize kernel build speed, with no no 
regard to latency (within SCHED_BATCH workloads). I suspect this will 
also maximize bandwidth of a lot of other real-world, highly parallel but 
interacting processing workloads.

[ I'd even be willing to rename it to SCHED_KBUILD, internally. ;-) ]

Thanks,

	Ingo