Re: [PATCH 2/2] powerpc: implement arch_scale_smt_power for Power7

Joel Schopp
2010-01-20T22:44:35Z

Peter Zijlstra wrote:
> On Wed, 2010-01-20 at 14:04 -0600, Joel Schopp wrote:
>
>> On Power7 processors running in SMT4 mode with 2, 3, or 4 idle threads
>> there is performance benefit to idling the higher numbered threads in
>> the core.
>>
>
> So this is an actual performance improvement, not only power savings?
>
Yes.

>
>
> And you just wrecked x86 ;-)
>
> It has an smt_power implementation that tries to measure smt gains using
> aperf/mperf, trouble is that this represents the actual performance not
> the capacity. This has the problem that when idle it represents 0
> capacity and will not attract work.
>
> Coming up with something that actually works there is on the todo list,
> I was thinking perhaps temporal maximums from !idle.
>
> So if you want to go with this, you'll need to stub out
> arch/x86/kernel/cpu/sched.c
>

OK. Guess I now will have a 3 patch series, with a patch to stub out
the x86 broken version.

Care to take Gautham's bugfix patch (patch 1/2) now, since it just fixes
a bug? You'll need it if you ever try to make the x86 broken version work.