Re: boot time, process start time, and NOW time

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

On Mon, 2004-08-16 at 15:41, Andrew Morton wrote:

> Where did this all end up?  Complaints about
> wandering start times are persistent, and it'd
> be nice to get some fix in place...

If you're interested in reducing (not solving)
the problem for the 2.6.x series, you might change
HZ to something that works better with the PIT.

Here is a table showing % error for various HZ choices:

wrongness_%   HZ_diff   PIT_#   HZ     actual_HZ   
-0.00150855  -0.001509  11932   100    99.998491  
-0.00150855  -0.009474   1900   628   627.990526  
-0.00083809  -0.003051   3278   364   363.996949  
-0.00083809  -0.008389   1192  1001  1000.991611  
+0.00000000  +0.000000  14551    82    82.000000  
+0.00008381  +0.000304   3287   363   363.000304  
+0.00008381  +0.000435   2299   519   519.000435  
+0.00008381  +0.000525   1903   627   627.000525  
+0.01525566  +0.152557   1193  1000  1000.152557  
+0.01860917  +0.190558   1165  1024  1024.190558

As you can see, 1000 HZ and 1024 HZ are really bad.
They're worse than typical quartz crystal variation.

The old 100 HZ tick was just barely tolerable.
While 82 is perfect, it's a bit low. :-(

Some of the other choices are nice. How about 363,
519, or 627?

For the AMD Elan: 300, 400, 600, 991, 1200
(the AMD Elan PIT runs at 1189200 instead of 1193182)