Messages in this thread Patch in this message | | | Date | Mon, 28 Jul 2003 14:55:51 -0700 | From | george anzinger <> | Subject | Re: Fw: missing #if for 1000 HZ |
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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 <albert@users.sourceforge.net> > To: linux-kernel@vger.kernel.org, Ulrich.Windl@rz.uni-regensburg.de > Cc: Andrew Morton <akpm@digeo.com>, 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
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