linux-kernel - [PATCH] ACPI: Idle C-states disabled by max

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Date:	Fri, 15 May 2009 01:40:01 -0400 (EDT)
From:	Len Brown <lenb@...nel.org>
To:	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Janne Kulmala <janne.t.kulmala@....fi>,
	Frans Pop <elendil@...net.nl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...e.hu>, johnstul@...ibm.com,
	linux-acpi@...r.kernel.org
Subject: [PATCH] ACPI: Idle C-states disabled by max_cstate should not disable
 the TSC

From: Len Brown <len.brown@...el.com>

Processor idle power states C2 and C3 stop the TSC on many machines.
Linux recognizes this situation and marks the TSC as unstable:

Marking TSC unstable due to TSC halts in idle

But if those same machines are booted with "processor.max_cstate=1",
then there is no need to validate C2 and C3, and no need to
disable the TSC, which can be reliably used as a clocksource.

Signed-off-by: Len Brown <len.brown@...el.com>
---
 drivers/acpi/processor_idle.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index e39a40a..e65476f 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -582,7 +582,7 @@ static int acpi_processor_power_verify(struct acpi_processor *pr)
 
 	pr->power.timer_broadcast_on_state = INT_MAX;
 
-	for (i = 1; i < ACPI_PROCESSOR_MAX_POWER; i++) {
+	for (i = 1; i < ACPI_PROCESSOR_MAX_POWER && i <= max_cstate; i++) {
 		struct acpi_processor_cx *cx = &pr->power.states[i];
 
 		switch (cx->type) {
-- 
1.6.3.1.9.g95405b

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