linux-kernel - Re: 2.6.25 regression: powertop says 120K wakeups/sec

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Date:	Fri, 28 Mar 2008 15:56:04 -0700
From:	Venki Pallipadi <venkatesh.pallipadi@...el.com>
To:	David Brownell <david-b@...bell.net>
Cc:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, "Rafael J. Wysocki" <rjw@...k.pl>,
	linux-acpi@...r.kernel.org, Len Brown <lenb@...nel.org>
Subject: Re: 2.6.25 regression: powertop says 120K wakeups/sec

On Fri, Mar 28, 2008 at 03:09:22PM -0700, David Brownell wrote:
> On Friday 28 March 2008, Pallipadi, Venkatesh wrote:
> > You should have a dmesg line which looks like
> > ACPI: CPU0 (power states: C1[C1] C2[C2]
> > Do you see C2 in such line?
> 
> Yes:
> 
> ACPI: CPU0 (power states: C1[C1] C2[C2])


David,

I think I figured out the bug...

Can you try the below patch and confirm that it works (over upstream - ignore
the earlier revert patch I sent to you).

Thanks,
Venki

----


Patch to fix huge number of wakeups reported due to recent changes in
processor_idle.c. The problem was that the entry_method determination was
broken due to one of the recent commits (bc71bec91f987) causing
C1 entry to not to go to halt. This should also fix the hang reported here.
http://bugzilla.kernel.org/show_bug.cgi?id=10093


Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>

---
 drivers/acpi/processor_idle.c |    4 ++++
 1 file changed, 4 insertions(+)

Index: linux-2.6/drivers/acpi/processor_idle.c
===================================================================
--- linux-2.6.orig/drivers/acpi/processor_idle.c	2008-03-28 15:31:13.000000000 -0700
+++ linux-2.6/drivers/acpi/processor_idle.c	2008-03-28 15:40:50.000000000 -0700
@@ -848,6 +848,7 @@ static int acpi_processor_get_power_info
 		/* all processors need to support C1 */
 		pr->power.states[ACPI_STATE_C1].type = ACPI_STATE_C1;
 		pr->power.states[ACPI_STATE_C1].valid = 1;
+		pr->power.states[ACPI_STATE_C1].entry_method = ACPI_CSTATE_HALT;
 	}
 	/* the C0 state only exists as a filler in our array */
 	pr->power.states[ACPI_STATE_C0].valid = 1;
@@ -960,6 +961,9 @@ static int acpi_processor_get_power_info
 				 cx.address);
 		}
 
+		if (cx.type == ACPI_STATE_C1) {
+			cx.valid = 1;
+		}
 
 		obj = &(element->package.elements[2]);
 		if (obj->type != ACPI_TYPE_INTEGER)
--
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