From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S271108AbTG1V4c (ORCPT ); Mon, 28 Jul 2003 17:56:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S271117AbTG1V4c (ORCPT ); Mon, 28 Jul 2003 17:56:32 -0400 Received: from gateway-1237.mvista.com ([12.44.186.158]:5623 "EHLO av.mvista.com") by vger.kernel.org with ESMTP id S271108AbTG1V41 (ORCPT ); Mon, 28 Jul 2003 17:56:27 -0400 Message-ID: <3F259BE7.9070403@mvista.com> Date: Mon, 28 Jul 2003 14:55:51 -0700 From: george anzinger User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.2) Gecko/20021202 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Andrew Morton CC: john stultz , Albert Cahalan , linux-kernel@vger.kernel.org, Ulrich.Windl@rz.uni-regensburg.de Subject: Re: Fw: missing #if for 1000 HZ References: <20030725203843.569863bc.akpm@osdl.org> In-Reply-To: <20030725203843.569863bc.akpm@osdl.org> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Andrew Morton wrote: > Guys? If I understand what is being done, he is right. By this measure the current error in the div (by shifting) is 2.4%. I wonder how this plays with(line 639): time_phase += time_adj; if (time_phase <= -FINENSEC) { long ltemp = -time_phase >> (SHIFT_SCALE - 10); time_phase += ltemp << (SHIFT_SCALE - 10); delta_nsec -= ltemp; } where, we are also using >>10 ~= /1000. I _think_ this ladder approximation only delays part of the correction but does not loose it, but the more eyes the better. -g > > Begin forwarded message: > > Date: 22 Jul 2003 21:01:16 -0400 > From: Albert Cahalan > To: linux-kernel@vger.kernel.org, Ulrich.Windl@rz.uni-regensburg.de > Cc: Andrew Morton , alan@redhat.com > Subject: missing #if for 1000 HZ > > > This should improve timekeeping a bit @ 1000 HZ. > > > diff -Naurd old/kernel/timer.c new/kernel/timer.c > --- old/kernel/timer.c 2003-07-18 17:27:01.000000000 -0400 > +++ new/kernel/timer.c 2003-07-18 17:32:19.000000000 -0400 > @@ -606,6 +606,15 @@ > else > time_adj += (time_adj >> 2) + (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); > +#endif > } > > /* in the NTP reference this is called "hardclock()" */ > > > > -- George Anzinger george@mvista.com High-res-timers: http://sourceforge.net/projects/high-res-timers/ Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml