Re: [PATCH] Re: boot time, process start time, and NOW time

[Albert Cahalan <albert@users.sf.net>]

On Mon, 2004-08-30 at 19:38, john stultz wrote:

> This isn't going to happen instantly by any means. I'm trying to
> get the time of day rework finished as soon as I can, but I've
> got the day job to do as well. In the mean time, we can staple gun
> any user visible exported HZ/jiffies values so they are accurate
> (using ACTHZ or gettimeofday), and also look into changing HZ to a
> less error-ful value.  HZ=1001 has been suggested and looks quite  
> promising (although /net/schec/estimator.c wants a power of 4).

Well, pick something else. Here's a list of choices with
error under 0.0025%, in the 240..1300 range, that can be
evenly divided by four.

Dropping back a bit would be good, to better tolerate        
systems with firmware that steals enough time to cause
lost clock ticks.

I like 400, 488, and 556. 864 and 1112 are decent too.
It might be useful having 400 as a multiple of 100.

I don't think /net/sched/estimator.c needs such
great accuracy. If that were sacrificed, one could
do much better with HZ at 363, 519, or 627.

%error       HZerror     PIT#    HZ   actual
-0.00217900  -0.007234   3594   332   331.992766
-0.00217900  -0.014469   1797   664   663.985531
-0.00217900  -0.021703   1198   996   995.978297
-0.00184378  -0.014676   1499   796   795.985324
-0.00150855  -0.004586   3925   304   303.995414
-0.00150855  -0.005732   3140   380   379.994268
-0.00150855  -0.006034   2983   400   399.993966
-0.00150855  -0.009474   1900   628   627.990526
-0.00150855  -0.011465   1570   760   759.988535
-0.00150855  -0.018947    950  1256  1255.981053
-0.00083809  -0.002581   3874   308   307.997419
-0.00083809  -0.003051   3278   364   363.996949
-0.00083809  -0.004794   2086   572   571.995206
-0.00083809  -0.004995   2002   596   595.995005
-0.00083809  -0.005163   1937   616   615.994837
-0.00083809  -0.006101   1639   728   727.993899
-0.00083809  -0.009588   1043  1144  1143.990412
-0.00083809  -0.009990   1001  1192  1191.990010
-0.00050285  -0.006376    941  1268  1267.993624
-0.00016762  -0.000483   4143   288   287.999517
-0.00016762  -0.000724   2762   432   431.999276
-0.00016762  -0.001448   1381   864   863.998552
+0.00050286  +0.001488   4031   296   296.001488
+0.00050286  +0.002796   2146   556   556.002796
+0.00050286  +0.005592   1073  1112  1112.005592
+0.00150859  +0.018163    991  1204  1204.018163
+0.00184384  +0.004499   4890   244   244.004499
+0.00184384  +0.008998   2445   488   488.008998
+0.00184384  +0.012022   1830   652   652.012022
+0.00184384  +0.013497   1630   732   732.013497
+0.00184384  +0.022495    978  1220  1220.022495
+0.00217909  +0.027282    953  1252  1252.027282