Re: Subject: [PATCH] cpuidle: Add a sysfs entry to disable specific C state for debug purpose.

Yanmin Zhang
2012-03-05T01:35:22Z

On Fri, 2012-03-02 at 14:23 -0800, Andrew Morton wrote:
> On Fri, 02 Mar 2012 08:17:33 +0800
> Yanmin Zhang <yanmin_zhang@linux.intel.com> wrote:
>
> > On Wed, 2012-02-29 at 04:55 +0000, Liu, ShuoX wrote:
> > > From: ShuoX Liu <shuox.liu@intel.com>
> > >
> > > Some C states of new CPU might be not good. One reason is BIOS might configure
> > > them incorrectly. To help developers root cause it quickly, the patch adds a
> > > new sysfs entry, so developers could disable specific C state manually.
> > >
> > > In addition, C state might have much impact on performance tuning, as it takes
> > > much time to enter/exit C states, which might delay interrupt processing. With
> > > the new debug option, developers could check if a deep C state could impact
> > > performance and how much impact it could cause.
> > >
> > > Signed-off-by: ShuoX Liu <shuox.liu@intel.com>
> > Andrew,
> >
> > Would you like to merge the patch into your testing tree?
>
> I can do that, but it's hardly my area and I can't comment on the
> desirability of the patch and Len is having quiet time. Perhaps the
> x86 guys can take a look please>
>
> > It's useful to help developers debug some issues.
>
> It would help developers more if it was documented a bit. As it
> stands, they'd be lucky if they even knew it existed.
>
> Looky:
>
> akpm:/usr/src/linux-3.3-rc5> grep -ril cpuidle Documentation
> Documentation/trace/events-power.txt
> Documentation/ABI/testing/sysfs-devices-system-cpu
> Documentation/kernel-parameters.txt
> Documentation/00-INDEX
> Documentation/cpuidle/core.txt
> Documentation/cpuidle/sysfs.txt
> Documentation/cpuidle/driver.txt
> Documentation/cpuidle/governor.txt
Thanks Andrew. We checked above document files. The best place to record
the new entry is Documentation/cpuidle/sysfs.txt. We would change it and
resend the patch.