Messages in this thread | | | Date | Mon, 6 Oct 2008 23:19:39 +0200 | From | Andi Kleen <> | Subject | Re: PATCH] ftrace: Add a C/P state tracer to help power optimization |
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On Mon, Oct 06, 2008 at 01:57:15PM -0700, Arjan van de Ven wrote: > > the problem is that higher up the actual P state isn't known.
My main worry is that every architecture is going to implement their own version of this plugin if there isn't some abstraction.
> > Also I suspect some higher level format would be good here too. > > Just put the frequency in? > > 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.
> > > > + ret = trace_seq_printf(s, "[%5ld.%09ld] > > > CSTATE: Going to C%i on cpu %i for %ld.%09ld\n", > > > + stamp.tv_sec, > > > + stamp.tv_nsec, > > > + it->state, iter->cpu, > > > + duration.tv_sec, > > > + duration.tv_nsec); > > > + if (it->type == POWER_PSTATE) > > > + ret = trace_seq_printf(s, "[%5ld.%09ld] > > > PSTATE: Going to P%i on cpu %i\n", > > > + stamp.tv_sec, > > > + stamp.tv_nsec, > > > + it->state, iter->cpu); > > > > I suspect a less verbose output format would be better. > why?
to shuffle less data around
> It's fine as it is, and it's actually human readable as well.
I suspect humans could well do with something more compact too
e.g.
CPU %d -> P%d
> > > > > > +{ > > > + if (!trace_power_enabled) > > > + return; > > > + > > > + memset(it, 0, sizeof(struct power_trace)); > > > > The memset seems redundant. > > it's free and it initializes the datastructure cleanly; and only when
AFAIK all data fields are init'ed anyways.
How is it free? I'm not sure gcc will optimize it away completely.
I thought the point of ftrace tracers was to be reasonably efficient when they are enabled? If efficiency doesn't matter you could as well use printk.
> > Hmm, that does a unconditional wake_up() in idle. Doesn't this cause > > a loop on UP? > > > > idle -> wakeup -> idle -> wakeup -> ... etc. > > > > Am I missing something? > > yes you're missing something ;-) > this code is called when going out of idle, not when going into idle.
Ok.
That means that when a CPU is idle forever there won't be any output?
-Andi
-- ak@linux.intel.com
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