[RFC] Enabling invariant TSC timecounter on SMP
Andriy Gapon
avg at FreeBSD.org
Wed Jun 1 05:40:37 UTC 2011
on 31/05/2011 23:16 Jung-uk Kim said the following:
> On Tuesday 31 May 2011 07:18 am, Andriy Gapon wrote:
>> on 24/05/2011 20:56 Jung-uk Kim said the following:
>>> I think it's about time to enable invariant TSC timecounter on
>>> SMP by default. Please see the attached patch. It is also
>>> available from here:
>>>
>>> http://people.freebsd.org/~jkim/tsc_smp_test4.diff
>>>
>>> avg convinced me enough that it should be an opt-out feature
>>> going forward. :-)
>>
>> Not sure if I really did that.
>> My position is this:
>> - if we think that TSC is SMP-safe then it should have the best
>> priority
>> - we should do our best to auto-guess if TSC is SMP-safe
>> unless a user explicitly overrides that property (either via
>> explicit testing or by making guesses based on CPU model or etc)
>
> I am sorry if I misunderstood your intention. However, I added
> explicit boot-time TSC sanity check (to do our best to auto-guess)
> and I think TSC is fairly SMP-safe. Hence, I thought that it is
> about time for the change.
In this case - yes. But I remember that you were thinking about either
improving or simplifying that check or both.
>>> Comments?
>>
>> Perhaps I missed it, but I don't remember the "lowres" part of the
>> patch being discussed.
>
> No, it wasn't discussed with you. Do you see any problem with that
> code?
I don't see any obvious problem, but I also don't understand rationale of using
smaller max_freq for the ncpus > 1 case.
Maybe these two logical changes should be done as two separate commits.
--
Andriy Gapon
More information about the freebsd-hackers
mailing list