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

From: Joel Schopp
Date: Wed Jan 20 2010 - 17:44:40 EST

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?

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

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.
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