non-invariant tsc and cputicker

[Andriy Gapon]

on 06/12/2010 19:42 Jung-uk Kim said the following:
> Sigh...  Please see the history of calcru() in 
> sys/kern/kern_resource.c.  Most important ones are:
> 
> http://svn.freebsd.org/viewvc/base?view=revision&revision=155444
> http://svn.freebsd.org/viewvc/base?view=revision&revision=155534
> 
> Basically, we chose efficiency over accuracy and you are suggesting 
> going backwards.

Well, I guess that it depends.

Looking at r155444 - the time is still going to be accounted in ticks (but
timecounter ticks).  BTW, I think that this quote says something: "On more modern
hardware no change in performance is seen." and that was ~5 years ago.

Looking at r155534 - the only change that is going to get undone is using TSC for
the accounting ticks, and that is only for machines with non-invariant TSC.  And I
think that all sufficiently modern machines have invariant TSC and, in Intel's
words, that's an architectural path going forward.

So, I don't think that I propose a dramatic change.
-- 
Andriy Gapon