non-invariant tsc and cputicker
avg at freebsd.org
Mon Dec 6 17:58:28 UTC 2010
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:
> 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.
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