Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750910AbVIUDYT (ORCPT ); Tue, 20 Sep 2005 23:24:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750908AbVIUDYT (ORCPT ); Tue, 20 Sep 2005 23:24:19 -0400 Received: from e33.co.us.ibm.com ([32.97.110.151]:47810 "EHLO e33.co.us.ibm.com") by vger.kernel.org with ESMTP id S1750906AbVIUDYS (ORCPT ); Tue, 20 Sep 2005 23:24:18 -0400 Subject: [PATCH] NTP shift_right cleanup (v. A3) From: john stultz To: Andrew Morton Cc: lkml , joe-lkml@rameria.de, George Anzinger , Ulrich Windl , Roman Zippel , yoshfuji@linux-ipv6.org In-Reply-To: <1127179730.11080.3.camel@cog.beaverton.ibm.com> References: <1126720091.3455.56.camel@cog.beaverton.ibm.com> <1127179730.11080.3.camel@cog.beaverton.ibm.com> Content-Type: text/plain Date: Tue, 20 Sep 2005 20:24:10 -0700 Message-Id: <1127273050.11080.34.camel@cog.beaverton.ibm.com> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 (2.2.3-2.fc4) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7316 Lines: 220 Andrew, After some close scrutiny I found a mistake in the A2 version of this patch. I guess it just goes to prove how difficult to read the current code is. In one part of the old patch, a nested if stated: if (ltemp > (MAXPHASE / MINSEC) << SHIFT_UPDATE) ltemp = (MAXPHASE / MINSEC) << SHIFT_UPDATE; However that only bounds ltemp if it is positive, when the current mainline code bounds it if it is negative as well. Replacing the above with: ltemp = min(ltemp, (MAXPHASE / MINSEC) << SHIFT_UPDATE); ltemp = max(ltemp, -(MAXPHASE / MINSEC) << SHIFT_UPDATE); Corrects the issue. Below is the corrected patch which should replace the ntp-shift_right-cleanup.patch file in your tree. Thanks -john Create a macro shift_right() that avoids the numerous ugly conditionals in the NTP code that look like: if(a < 0) b = -(-a >> shift); else b = a >> shift; Replacing it with: b = shift_right(a, shift); This should have zero effect on the logic, however it should probably have a bit of testing just to be sure. Also replace open-coded min/max with the macros. Signed-off-by : John Stultz --- include/linux/timex.h | 7 +++++++ kernel/time.c | 25 ++++++------------------- kernel/timer.c | 48 ++++++++++-------------------------------------- 3 files changed, 23 insertions(+), 57 deletions(-) diff --git a/include/linux/timex.h b/include/linux/timex.h --- a/include/linux/timex.h +++ b/include/linux/timex.h @@ -282,6 +282,13 @@ static inline int ntp_synced(void) return !(time_status & STA_UNSYNC); } +/* Required to safely shift negative values */ +#define shift_right(x, s) ({ \ + __typeof__(x) __x = (x); \ + __typeof__(s) __s = (s); \ + __x < 0 ? -(-__x >> __s) : __x >> __s; \ +}) + #ifdef CONFIG_TIME_INTERPOLATION diff --git a/kernel/time.c b/kernel/time.c --- a/kernel/time.c +++ b/kernel/time.c @@ -338,30 +338,20 @@ int do_adjtimex(struct timex *txc) if (mtemp >= MINSEC) { ltemp = (time_offset / mtemp) << (SHIFT_USEC - SHIFT_UPDATE); - if (ltemp < 0) - time_freq -= -ltemp >> SHIFT_KH; - else - time_freq += ltemp >> SHIFT_KH; + time_freq += shift_right(ltemp, SHIFT_KH); } else /* calibration interval too short (p. 12) */ result = TIME_ERROR; } else { /* PLL mode */ if (mtemp < MAXSEC) { ltemp *= mtemp; - if (ltemp < 0) - time_freq -= -ltemp >> (time_constant + - time_constant + - SHIFT_KF - SHIFT_USEC); - else - time_freq += ltemp >> (time_constant + + time_freq += shift_right(ltemp,(time_constant + time_constant + - SHIFT_KF - SHIFT_USEC); + SHIFT_KF - SHIFT_USEC)); } else /* calibration interval too long (p. 12) */ result = TIME_ERROR; } - if (time_freq > time_tolerance) - time_freq = time_tolerance; - else if (time_freq < -time_tolerance) - time_freq = -time_tolerance; + time_freq = min(time_freq, time_tolerance); + time_freq = max(time_freq, -time_tolerance); } /* STA_PLL || STA_PPSTIME */ } /* txc->modes & ADJ_OFFSET */ if (txc->modes & ADJ_TICK) { @@ -384,10 +374,7 @@ leave: if ((time_status & (STA_UNSYNC|ST if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT) txc->offset = save_adjust; else { - if (time_offset < 0) - txc->offset = -(-time_offset >> SHIFT_UPDATE); - else - txc->offset = time_offset >> SHIFT_UPDATE; + txc->offset = shift_right(time_offset, SHIFT_UPDATE); } txc->freq = time_freq + pps_freq; txc->maxerror = time_maxerror; diff --git a/kernel/timer.c b/kernel/timer.c --- a/kernel/timer.c +++ b/kernel/timer.c @@ -703,23 +703,13 @@ static void second_overflow(void) * the adjustment over not more than the number of * seconds between updates. */ - if (time_offset < 0) { - ltemp = -time_offset; - if (!(time_status & STA_FLL)) - ltemp >>= SHIFT_KG + time_constant; - if (ltemp > (MAXPHASE / MINSEC) << SHIFT_UPDATE) - ltemp = (MAXPHASE / MINSEC) << SHIFT_UPDATE; - time_offset += ltemp; - time_adj = -ltemp << (SHIFT_SCALE - SHIFT_HZ - SHIFT_UPDATE); - } else { ltemp = time_offset; if (!(time_status & STA_FLL)) - ltemp >>= SHIFT_KG + time_constant; - if (ltemp > (MAXPHASE / MINSEC) << SHIFT_UPDATE) - ltemp = (MAXPHASE / MINSEC) << SHIFT_UPDATE; + ltemp = shift_right(ltemp, SHIFT_KG + time_constant); + ltemp = min(ltemp, (MAXPHASE / MINSEC) << SHIFT_UPDATE); + ltemp = max(ltemp, -(MAXPHASE / MINSEC) << SHIFT_UPDATE); time_offset -= ltemp; time_adj = ltemp << (SHIFT_SCALE - SHIFT_HZ - SHIFT_UPDATE); - } /* * Compute the frequency estimate and additional phase @@ -736,30 +726,19 @@ static void second_overflow(void) STA_PPSWANDER | STA_PPSERROR); } ltemp = time_freq + pps_freq; - if (ltemp < 0) - time_adj -= -ltemp >> - (SHIFT_USEC + SHIFT_HZ - SHIFT_SCALE); - else - time_adj += ltemp >> - (SHIFT_USEC + SHIFT_HZ - SHIFT_SCALE); + time_adj += shift_right(ltemp,(SHIFT_USEC + SHIFT_HZ - SHIFT_SCALE)); #if HZ == 100 /* Compensate for (HZ==100) != (1 << SHIFT_HZ). * Add 25% and 3.125% to get 128.125; => only 0.125% error (p. 14) */ - if (time_adj < 0) - time_adj -= (-time_adj >> 2) + (-time_adj >> 5); - else - time_adj += (time_adj >> 2) + (time_adj >> 5); + time_adj += shift_right(time_adj, 2) + shift_right(time_adj, 5); #endif #if HZ == 1000 /* Compensate for (HZ==1000) != (1 << SHIFT_HZ). * Add 1.5625% and 0.78125% to get 1023.4375; => only 0.05% error (p. 14) */ - if (time_adj < 0) - time_adj -= (-time_adj >> 6) + (-time_adj >> 7); - else - time_adj += (time_adj >> 6) + (time_adj >> 7); + time_adj += shift_right(time_adj, 6) + shift_right(time_adj, 7); #endif } @@ -778,10 +757,8 @@ static void update_wall_time_one_tick(vo * Limit the amount of the step to be in the range * -tickadj .. +tickadj */ - if (time_adjust > tickadj) - time_adjust_step = tickadj; - else if (time_adjust < -tickadj) - time_adjust_step = -tickadj; + time_adjust_step = min(time_adjust_step, (long)tickadj); + time_adjust_step = max(time_adjust_step, (long)-tickadj); /* Reduce by this step the amount of time left */ time_adjust -= time_adjust_step; @@ -792,13 +769,8 @@ static void update_wall_time_one_tick(vo * advance the tick more. */ time_phase += time_adj; - if (time_phase <= -FINENSEC) { - long ltemp = -time_phase >> (SHIFT_SCALE - 10); - time_phase += ltemp << (SHIFT_SCALE - 10); - delta_nsec -= ltemp; - } - else if (time_phase >= FINENSEC) { - long ltemp = time_phase >> (SHIFT_SCALE - 10); + if ((time_phase >= FINENSEC) || (time_phase <= -FINENSEC)) { + long ltemp = shift_right(time_phase, (SHIFT_SCALE - 10)); time_phase -= ltemp << (SHIFT_SCALE - 10); delta_nsec += ltemp; } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/