Re: [PATCH] pm: Add runtime PM statistics to sysfs

[Arjan van de Ven]

On Fri, 9 Jul 2010 15:04:59 +0800
Ming Lei <tom.leiming@xxxxxxxxx> wrote:

> 2010/7/9 Arjan van de Ven <arjan@xxxxxxxxxxxxx>:
> > From: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
> > diff --git a/include/linux/pm.h b/include/linux/pm.h
> > index 8e258c7..dca597f 100644
> > --- a/include/linux/pm.h
> > +++ b/include/linux/pm.h
> > @@ -476,9 +476,15 @@ struct dev_pm_info {
> >    Âenum rpm_request    Ârequest;
> >    Âenum rpm_status     runtime_status;
> >    Âint           runtime_error;
> > +    unsigned long      active_jiffies;
> > +    unsigned long      suspended_jiffies;
> > +    unsigned long      accounting_timestamp;
> > Â#endif
> > Â};
> 
> USB subsystem has implemented the function already, and only two
> variables are enough to do the statistics. Suggest you to make a
> reference to usb implementation, maybe sizeof(unsigned long) bytes
> per device can be saved.
> 

I did look at the USB implementation, and it is very clever. But it's
more complex at the same time, because you no longer can just read out
the time stamps, you need to look at the current device state each time
to either subtract jiffies or not. 

by having the timestamp as a separate variable all the code gets
a lot simpler..... sometimes simple over clever is the right thing to
do.


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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