kernel/linux
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ synced 2026-10-28 20:03:05 +00:00
Code Issues Releases Packages Activity

ntp: adjust SHIFT_PLL to improve NTP convergence

Browse source 
The conversion to the ntpv4 reference model
f199239373 ("ntp: convert to the NTP4
reference model") in 2.6.19 added nanosecond resolution the adjtimex
interface, but also changed the "stiffness" of the frequency adjustments,
causing NTP convergence time to greatly increase.

SHIFT_PLL, which reduces the stiffness of the freq adjustments, was
designed to be inversely linked to HZ, and the reference value of 4 was
designed for Unix systems using HZ=100.  However Linux's clock steering
code mostly independent of HZ.

So this patch reduces the SHIFT_PLL value from 4 to 2, which causes NTPd
behavior to match kernels prior to 2.6.19, greatly reducing convergence
times, and improving close synchronization through environmental thermal
changes.

The patch also changes some l's to L's in nearby code to avoid misreading
50l as 501.

[ Impact: tweak NTP algorithm for faster convergence ]

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: zippel@linux-m68k.org
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
LKML-Reference: <200905051956.n45JuVo9025575@imap1.linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
john stultz 2009-05-06 11:43:57 +02:00 • committed by Ingo Molnar
commit 22cfbbfd9f
1 changed files with 31 additions and 11 deletions
Download patch file Download diff file Expand all files Collapse all files