Re: [PATCH] x86, msr: Allow read access to /dev/cpu/X/msr

[Ingo Molnar <mingo@kernel.org>]

* Peter Zijlstra <peterz@infradead.org> wrote:

> On Tue, Jun 30, 2015 at 08:20:55AM -0400, Prarit Bhargava wrote:
> > it seems like visiting changes on each of these packages (and the other
> > packages that I'm sure I've missed) will be moderately difficult.
> > 
> > Thoughts?
> 
> Start by changing the ones users want to run most and leave the rest
> requiring root privs until someone has the time to convert them.

Yes, start by just converting the ones used by a single tool, say turbostat, and 
then convert turbostat (while keeping /dev/msr fall-back code as well) just to see 
what the tooling fallout is.

> Its not like we can remove the msr driver any time soon anyway.

Yes.

> So I would suggest starting with the perf MSR driver thingy for all
> those MSRs that count things and see if you can convert say
> turbostat/cpufrequtils/powertop over to that.

One of those tools would be enough, to keep the complexity of the initial 
submission low - and to allow a change of plans if necessary.

> I suspect there's MSR that are useful to expose but are not counting, I'm not 
> sure perf is the right interface for those.
>
> Making an inventory on which MSRs are required by these tools and what kind of 
> data they provide might give a good idea on how to continue.
> 
> If most of these tools only use counting MSRs that can be serviced with the 
> perf-msr driver then that would be great.

Fully agreed!

Thanks,

	Ingo