lkml.org 
[lkml]   [2004]   [Aug]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: boot time, process start time, and NOW time
From
Date
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)


-
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/

\
 
 \ /
  Last update: 2005-03-22 14:05    [from the cache]
©2003-2011 Jasper Spaans