linux-kernel - Re: High CPU load when machine is idle (related to PROBLEM: Unusually high load average when idle in 2.6.35, 2.6.35.1 and later)

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Message-ID: <1290888920.32004.1.camel@laptop>
Date:	Sat, 27 Nov 2010 21:15:20 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Damien Wyart <damien.wyart@...e.fr>
Cc:	tmhikaru@...il.com, Venkatesh Pallipadi <venki@...gle.com>,
	Chase Douglas <chase.douglas@...onical.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Kyle McMartin <kyle@...artin.ca>
Subject: Re: High CPU load when machine is idle (related to PROBLEM:
 Unusually high load average when idle in 2.6.35, 2.6.35.1 and later)

On Thu, 2010-11-25 at 15:03 +0100, Peter Zijlstra wrote:

> I'll try and get around to it somewhere this week again.

How does this work for you? Its hideous but lets start simple.

---
 kernel/sched.c |    5 +++++
 kernel/timer.c |   14 ++++++++++++--
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index dc91a4d..2ebb07c 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3223,6 +3223,11 @@ static void calc_load_account_active(struct rq *this_rq)
 	this_rq->calc_load_update += LOAD_FREQ;
 }
 
+void calc_load_account_this(void)
+{
+	calc_load_account_active(this_rq());
+}
+
 /*
  * The exact cpuload at various idx values, calculated at every tick would be
  * load = (2^idx - 1) / 2^idx * load + 1 / 2^idx * cur_load
diff --git a/kernel/timer.c b/kernel/timer.c
index 68a9ae7..af095c0 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1315,11 +1315,21 @@ void run_local_timers(void)
  * jiffies is defined in the linker script...
  */
 
+extern void calc_load_account_this(void);
+
 void do_timer(unsigned long ticks)
 {
-	jiffies_64 += ticks;
+	if (ticks > 1) {
+		while (ticks--) {
+			jiffies_64++;
+			calc_load_account_this();
+			calc_global_load();
+		}
+	} else {
+		jiffies_64 += ticks;
+		calc_global_load();
+	}
 	update_wall_time();
-	calc_global_load();
 }
 
 #ifdef __ARCH_WANT_SYS_ALARM

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