[ntp:questions] setting CONFIG_HZ=2000 makes ntpd go crazy

Hai Zaar haizaar at gmail.com
Wed Feb 15 16:10:36 UTC 2006

Dear list, I've posted the forwarded message to linux-kernel mailing
list but there were no any answers. May be here someone can provide a


P.S I'm not on the list, so please CC me.

---------- Forwarded message ----------
From: Hai Zaar <haizaar at gmail.com>
Date: Feb 13, 2006 8:58 AM
Subject: setting CONFIG_HZ=2000 makes ntpd go crazy
To: linux-kernel at vger.kernel.org
Cc: "Yanover, Igor" <igor.yanover at intel.com>

Dear list,
I use the patch below to speed up HZ from 1000 to 2000. I use this hack
starting from kernel  2.6.7 and I have not experienced any particular
problems. Recently I've started to use NTP and  have noticed that ntp
client loose synchronization, if this patch is applied, i.e. it
connects, synchronizes, and then after a few polls,  jitter just jumps
to 5 digit number. I've rechecked the behavior on the kernel 2.6.11
and results are the same - applied patch just "skews up" ntpd, while
there are no any problems with vanilla kernels.

Is the patch incorrect in any way?

P.S. I'm not on the list, so please CC me. Thanks.
The patch ajusts kernel internal clock timer to 2000HZ instead of 1000HZ. This
is required to decrease response time of some drivers (currently rocket.ko).

Author: Igor Yanover <igor at yanover.name>
Crafted for 2.6.15 by:  Michael Goldman <haizaar at gmail.com>

--- kernel-2.6.15/include/linux/jiffies.h.orig  2006-02-07
12:59:20.000000000 +0200
+++ kernel-2.6.15/include/linux/jiffies.h       2006-02-07
13:00:50.000000000 +0200
@@ -38,6 +38,8 @@
 # define SHIFT_HZ      9
  #elif HZ >= 768 && HZ < 1536
 # define SHIFT_HZ      10
+#elif HZ >= 1536 && HZ < 3072
+# define SHIFT_HZ  11
 # error You lose.
--- kernel-2.6.15/kernel/Kconfig.hz.orig        2006-01-03
05:21:10.000000000 +0200
+++ kernel-2.6.15/kernel/Kconfig.hz     2006-02-07 18:44:03.000000000 +0200
@@ -36,6 +36,11 @@
         1000 HZ is the preferred choice for desktop systems and other
         systems requiring fast interactive responses to events.

+       config HZ_2000
+               bool "2000 HZ"
+       help
+        2000 HZ is hand crafted for software realtime. Use on your own risk.

 config HZ
@@ -43,4 +48,5 @@
        default 100 if HZ_100
        default 250 if HZ_250
        default 1000 if HZ_1000
+       default 2000 if HZ_2000



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