Re: [PATCH] ACPI: Fix the incorrect calculation about C-state idle time

[Len Brown <lenb@kernel.org>]

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thanks,
Len Brown, Intel Open Source Technology Center

On Wed, 2 Jun 2010, Venkatesh Pallipadi wrote:

> On Tue, Jun 1, 2010 at 8:04 PM,  <yakui.zhao@intel.com> wrote:
> > From: Zhao Yakui <yakui.zhao@intel.com>
> >
> > The C-state idle time is not calculated correctly, which will return the wrong
> > residency time in C-state. It will have the following effects:
> >   1.  The system can't choose the deeper C-state when it is idle next time.
> > Of course the system power is increased. E.g. On one server machine about 40W
> > idle power is increased.
> >   2.  The powertop shows that it will stay in C0 running state about 95% time
> > although the system is idle at most time.
> 
> This was a bug from my recent patch here :-(
> http://marc.info/?l=linux-acpi&m=127198016715509&w=2
> 
> Thanks for catching this..
> 
> Acked-by: Venkatesh Pallipadi <venki@google.com>

Another question about that patch...
regarding sched_clock_idle_wakeup_event().
Why do we call it for _simple and _bm, but not for _c1?
Why do we bother calculating its sleep_ticks*PM_TIMER_TICK_NS
argument, when that argument is never accessed?

thanks,
Len Brown, Intel Open Source Technology Center