From da939387ca2732b7ac941d0452185bb2a2d366b0 Mon Sep 17 00:00:00 2001
From: chris41g <chriswhite41g@gmail.com>
Date: Mon, 6 Aug 2012 11:11:35 -0500
Subject: [PATCH] kernel:sched: LOAD_FREQ (4*HZ+61) avoids loadavg Moire

LOAD_FREQ is (5*HZ+1) to avoid high load average when idle:
http://kerneltrap.org/mailarchive/linux-kernel/2007/10/3/328568

I suggest (4*HZ+61) for a better distribution.

With some seconds based load (like SSL heartbeats)
and LOAD_FREQ at (5*HZ+1) I see Moire patterns like inverse sawtooth,
since 2 or 3 probes hit the jobs (load increases quickly),
followed by several probes missing it.

A 4.61 sec interval gives optimal distribution over when within a
second a probe is taken, as .61 is close to golden ratio phi 1.618...
(test in http://ripke.com/goldenratio.c).

12*4.61 = 55.32 secs is still close to a minute,
and 13*4.61=59.93 is even closer than the current 12*5.01=60.12
(with exponents EXP_x adjusted to a ratio of 13 instead of 12).
---
 include/linux/sched.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index c4703f5c..8b84dfd2 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -122,7 +122,7 @@ extern void get_avenrun(unsigned long *loads, unsigned long offset, int shift);
 
 #define FSHIFT		11		/* nr of bits of precision */
 #define FIXED_1		(1<<FSHIFT)	/* 1.0 as fixed-point */
-#define LOAD_FREQ	(5*HZ+1)	/* 5 sec intervals */
+#define LOAD_FREQ	((4*HZ+61)  /* 4.61 sec intervals */
 #define EXP_1		1884		/* 1/exp(5sec/1min) as fixed-point */
 #define EXP_5		2014		/* 1/exp(5sec/5min) */
 #define EXP_15		2037		/* 1/exp(5sec/15min) */