non-invariant tsc and cputicker
Jung-uk Kim
jkim at FreeBSD.org
Fri Dec 3 18:06:02 UTC 2010
On Friday 03 December 2010 12:26 pm, Andriy Gapon wrote:
> FreeBSD uses cpu_ticks [function pointer] in a few places for a few
> things like process CPU time accounting. On x86 cpu_ticks always
> points to rdtsc. If TSC is not invariant that leads to incorrect
> accounting of "CPU ticks". The code pretends to try to handle
> changing cpufreq levels, but does that incorrectly.
Arg... Probably it is my fault. :-(
> I think that we could use a selected timecounter instead of "raw"
> TSC if the latter is not invariant. In this case cpu_ticks calls
> would be slightly costlier, but always correct.
>
> The change is quite trivial:
> http://people.freebsd.org/~avg/tsc-cputicker.diff
>
> What do you think?
Why don't we just fix it properly?
> P.S. it's probably a good idea to merge i386 and amd64 tsc.c files
> into a common x86 version, which would be the same as i386 version,
> which seems to be generic enough.
Agreed.
Thanks,
Jung-uk Kim
More information about the freebsd-current
mailing list