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

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Message-Id: <20120302142303.648285a7.akpm@linux-foundation.org>
Date:	Fri, 2 Mar 2012 14:23:03 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	yanmin_zhang@...ux.intel.com
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Brown, Len" <len.brown@...el.com>,
	"Liu, ShuoX" <shuox.liu@...el.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: Subject: [PATCH] cpuidle: Add a sysfs entry to disable specific
 C state for debug purpose.

On Fri, 02 Mar 2012 08:17:33 +0800
Yanmin Zhang <yanmin_zhang@...ux.intel.com> wrote:

> On Wed, 2012-02-29 at 04:55 +0000, Liu, ShuoX wrote:
> > From: ShuoX Liu <shuox.liu@...el.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@...el.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

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