Re: [RFC PATCH v2 0/4] CPUs capacity information for heterogeneous systems

Juri Lelli
2016-01-20T10:25:24Z

On 19/01/16 17:50, Mark Brown wrote:
> On Tue, Jan 19, 2016 at 04:05:51PM +0100, Peter Zijlstra wrote:
> > On Fri, Jan 08, 2016 at 02:09:28PM +0000, Juri Lelli wrote:
>
> > > cons: - not easy to come up with a clean solution, as it seems interaction
> > > with several subsystems (e.g., cpufreq) is required
> > > - not easy to agree upon a single benchmark (that has to be both
> > > representative and simple enough to run at boot)
> > > - numbers might (and do) vary from boot to boot
>
> > This last point is a total pain for benchmarking, it means nothing is
> > every reproducible.
>
> > Therefore, I would always augment the above (2) with the below (3), such
> > that you can overwrite the results with a known stable set of numbers:
>
> The suggestion when the previous version was being discussed was that
> there are supposed to be some other knobs one uses for tuning and one
> was never supposed to use these numbers.

Right, DT solution might live without a sysfs interface, as you want to
use those other knobs for runtime tuning. Dynamic solution instead, and
I think this is what Peter was also pointing out, will most probably
require a sysfs interface for cases in which variation of default values
from boot to boot is not acceptable.