linux-kernel - [PATCH] sched_clock: fix NOHZ interaction

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Message-Id: <1220281088.8426.63.camel@twins>
Date:	Mon, 01 Sep 2008 16:58:08 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Avi Kivity <avi@...ranet.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH] sched_clock: fix NOHZ interaction

Avi, the below fixes it for me..


---
Subject: sched_clock: fix NOHZ interaction
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Date: Mon Sep 01 16:44:23 CEST 2008

If HLT stops the TSC, we'll fail to account idle time, thereby inflating the
actual process times. Fix this by re-calibrating the clock against GTOD when 
leaving nohz mode.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
 kernel/time/tick-sched.c |    3 +++
 1 file changed, 3 insertions(+)

Index: linux-2.6/kernel/time/tick-sched.c
===================================================================
--- linux-2.6.orig/kernel/time/tick-sched.c
+++ linux-2.6/kernel/time/tick-sched.c
@@ -162,6 +162,8 @@ void tick_nohz_stop_idle(int cpu)
 		ts->idle_lastupdate = now;
 		ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
 		ts->idle_active = 0;
+
+		sched_clock_idle_wakeup_event(0);
 	}
 }
 
@@ -177,6 +179,7 @@ static ktime_t tick_nohz_start_idle(stru
 	}
 	ts->idle_entrytime = now;
 	ts->idle_active = 1;
+	sched_clock_idle_sleep_event();
 	return now;
 }
 


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