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

[john stultz <johnstul@us.ibm.com>]

On Mon, 2004-08-16 at 16:24, Albert Cahalan wrote:
> 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?

What about 1001? That looks reasonably accurate.

thanks
-john