linux-kernel - [PATCH] sched: Notify hrtimer users of switches to NOHZ mode

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Date:	Tue, 18 Jan 2011 22:46:34 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] sched: Notify hrtimer users of switches to NOHZ mode

When NOHZ=y and high res timers are disabled (via cmdline or
Kconfig) tick_nohz_switch_to_nohz() will notify the user about
switching into NOHZ mode. Nothing is printed for the case where
HIGH_RES_TIMERS=y. Fix this for the HIGH_RES_TIMERS=y case by
duplicating the printk from the low res NOHZ path in the high res
NOHZ path.

Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
---

This confused me since I was thinking 'dmesg | grep -i NOHZ' would
tell me if NOHZ was enabled, but if I have hrtimers there is
nothing. If we don't do this we should probably remove the original
printk.

 kernel/time/tick-sched.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 3e216e0..6c012c5 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -795,8 +795,11 @@ void tick_setup_sched_timer(void)
 	}
 
 #ifdef CONFIG_NO_HZ
-	if (tick_nohz_enabled)
+	if (tick_nohz_enabled) {
 		ts->nohz_mode = NOHZ_MODE_HIGHRES;
+		pr_info("Switched to NOHz mode on CPU #%d\n",
+				smp_processor_id());
+	}
 #endif
 }
 #endif /* HIGH_RES_TIMERS */
-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

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