Messages in this thread | | | Date | Mon, 6 Oct 2008 23:34:18 +0200 | From | Andi Kleen <> | Subject | Re: PATCH] ftrace: Add a C/P state tracer to help power optimization |
| |
On Mon, Oct 06, 2008 at 02:21:31PM -0700, Arjan van de Ven wrote: > > > the link between P states and frequency is... rather lose. > > > Especially with Turbo Mode it no longer is really relevant to list > > > frequencies. > > > > It would probably be less confusing for everyone if the higher level > > cpufreq layers reported the correct frequency for turbo mode too. > > I haven't checked how complicated this would be. > > it's impossible until after the fact; you don't know which frequencies > you got until you check back later.
Well it could do that couldn't it? Ok not sure how big the cost would be.
I can just imagine Turbo mode becoming a FAQ on this list and having better reporting upfront might mitigate this a bit.
> > > > Ok. > > > > That means that when a CPU is idle forever there won't be any output? > > correct; it'll wait until it stops being idle before telling you how > long it was idle. > > if it really bothers you we could do a dummy broadcast ipi on shutting > down the tracer.. in practice it's not a problem.
Or just mark entry/exit, but you just need a wakeup threshold to avoid the loop. A wakeup threshold seems like a good idea anyways though, just to get better efficiency on larger systems.
> (we wake up all cpus all the time)
I assume that will change in the future and might even not true anymore on some special stripped down configurations.
-Andi
-- ak@linux.intel.com
| |