From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753314AbYGUPxd (ORCPT ); Mon, 21 Jul 2008 11:53:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751748AbYGUPxQ (ORCPT ); Mon, 21 Jul 2008 11:53:16 -0400 Received: from linux-m68k.xs4all.nl ([82.95.193.92]:48235 "EHLO scrub.xs4all.nl" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751509AbYGUPxP (ORCPT ); Mon, 21 Jul 2008 11:53:15 -0400 Message-Id: <20080721030306.837057486@linux-m68k.org> References: <20080721030005.559625052@linux-m68k.org> User-Agent: quilt/0.46-1 Date: Mon, 21 Jul 2008 05:00:06 +0200 From: zippel@linux-m68k.org To: akpm@linux-foundation.org Cc: johnstul@us.ibm.com, linux-kernel@vger.kernel.org Subject: [PATCH 1/3] clocksource: keep track of original clocksource frequency Content-Disposition: inline; filename=clocksource_mult_orig Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: John Stultz The clocksource frequency is represented by clocksource->mult/2^(clocksource->shift). Currently, when NTP makes adjustments to the clock frequency, they are made directly to the mult value. This has the drawback that once changed, we cannot know what the orignal mult value was, or how much adjustment has been applied. This property causes problems in calculating proper ntp intervals when switching back and forth between clocksources. This patch separates the current mult value into a mult and mult_orig pair. The mult_orig value stays constant, while the ntp clocksource adjustments are done only to the mult value. This allows for correct ntp interval calculation and additionally lays the groundwork for a new notion of time, what I'm calling the monotonic-raw time, which is introduced in a following patch. Signed-off-by: John Stultz Signed-off-by: Roman Zippel --- include/linux/clocksource.h | 11 +++++++---- kernel/time/clocksource.c | 3 +++ kernel/time/jiffies.c | 1 + 3 files changed, 11 insertions(+), 4 deletions(-) Index: linux-2.6/include/linux/clocksource.h =================================================================== --- linux-2.6.orig/include/linux/clocksource.h +++ linux-2.6/include/linux/clocksource.h @@ -45,7 +45,8 @@ struct clocksource; * @read: returns a cycle value * @mask: bitmask for two's complement * subtraction of non 64 bit counters - * @mult: cycle to nanosecond multiplier + * @mult: cycle to nanosecond multiplier (adjusted by NTP) + * @mult_orig: cycle to nanosecond multiplier (unadjusted by NTP) * @shift: cycle to nanosecond divisor (power of two) * @flags: flags describing special properties * @vread: vsyscall based read @@ -63,6 +64,7 @@ struct clocksource { cycle_t (*read)(void); cycle_t mask; u32 mult; + u32 mult_orig; u32 shift; unsigned long flags; cycle_t (*vread)(void); @@ -201,16 +203,17 @@ static inline void clocksource_calculate { u64 tmp; - /* XXX - All of this could use a whole lot of optimization */ + /* Do the ns -> cycle conversion first, using original mult */ tmp = length_nsec; tmp <<= c->shift; - tmp += c->mult/2; - do_div(tmp, c->mult); + tmp += c->mult_orig/2; + do_div(tmp, c->mult_orig); c->cycle_interval = (cycle_t)tmp; if (c->cycle_interval == 0) c->cycle_interval = 1; + /* Go back from cycles -> shifted ns, this time use ntp adjused mult */ c->xtime_interval = (u64)c->cycle_interval * c->mult; } Index: linux-2.6/kernel/time/clocksource.c =================================================================== --- linux-2.6.orig/kernel/time/clocksource.c +++ linux-2.6/kernel/time/clocksource.c @@ -325,6 +325,9 @@ int clocksource_register(struct clocksou unsigned long flags; int ret; + /* save mult_orig on registration */ + c->mult_orig = c->mult; + spin_lock_irqsave(&clocksource_lock, flags); ret = clocksource_enqueue(c); if (!ret) Index: linux-2.6/kernel/time/jiffies.c =================================================================== --- linux-2.6.orig/kernel/time/jiffies.c +++ linux-2.6/kernel/time/jiffies.c @@ -61,6 +61,7 @@ struct clocksource clocksource_jiffies = .read = jiffies_read, .mask = 0xffffffff, /*32bits*/ .mult = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */ + .mult_orig = NSEC_PER_JIFFY << JIFFIES_SHIFT, .shift = JIFFIES_SHIFT, }; --