From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760963AbXKAP3p (ORCPT ); Thu, 1 Nov 2007 11:29:45 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754625AbXKAP3i (ORCPT ); Thu, 1 Nov 2007 11:29:38 -0400 Received: from ftp.linux-mips.org ([194.74.144.162]:57013 "EHLO ftp.linux-mips.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754138AbXKAP3h (ORCPT ); Thu, 1 Nov 2007 11:29:37 -0400 Date: Thu, 1 Nov 2007 15:29:14 +0000 From: Ralf Baechle To: linux-kernel@vger.kernel.org Subject: CLOCK_TICK_RATE in NTP code Message-ID: <20071101152914.GA19732@linux-mips.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.14 (2007-02-12) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org kernel/time/ntp.c contains the following piece of code: #define CLOCK_TICK_OVERFLOW (LATCH * HZ - CLOCK_TICK_RATE) #define CLOCK_TICK_ADJUST (((s64)CLOCK_TICK_OVERFLOW * NSEC_PER_SEC) / \ (s64)CLOCK_TICK_RATE) static void ntp_update_frequency(void) { u64 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ) << TICK_LENGTH_SHIFT; second_length += (s64)CLOCK_TICK_ADJUST << TICK_LENGTH_SHIFT; second_length += (s64)time_freq << (TICK_LENGTH_SHIFT - SHIFT_NSEC); tick_length_base = second_length; do_div(second_length, HZ); tick_nsec = second_length >> TICK_LENGTH_SHIFT; do_div(tick_length_base, NTP_INTERVAL_FREQ); } So it uses CLOCK_TICK_RATE which on many systems but not all is defined to the i8253 input clock. But timekeeping on anything remotely modern makes little use of the i8253 so I wonder the intent was here. Ralf