TSC timekeeping and cpu states

[Ian Smith]

On Mon, 14 Aug 2017 09:48:07 -0700, Kevin Oberman wrote:
 > On Mon, Aug 14, 2017 at 8:38 AM, Ian Smith <smithi at nimnet.asn.au> wrote:
[..]
 > >  > > As far as possible TSC impact, I think older processors had TSC
 > >  > > issues when not all cores ran with the same clock speed. That said,
 > >  > > I am not remotely expert on such issues, so don't take this too
 > >  > > seriously.
 > >
 > > I wasn't aware that FreeBSD could yet do different freqs on different
 > > cores?  But I'm less expert than Kevin, and certainly behind the times.
[..]
 > I guess I need to clarify. No, FreeBSD does not have the ability to tun
 > different cores at different frequencies. I seem to recall that TCC on some
 > processors could adjust the frequency of a core exceeding a defined
 > temperature, skipping N of every 8 clock cycles to slow the processor and
 > reduce the temperature. This is what TCC was designed for. It is entirely
 > possible that I am not correctly remembering the details of the issue, but
 > it could only be resolved by switching from TCC to another clocking system.
 > 
 > If memory serves, and it may not, there was an issue a few years ago (jhb@
 > worked the issue) where TSC was varying with frequency and that caused
 > clock drift. I believe all "modern" processors do not have this issue and
 > it seems unlikely that any system running 24 cores is old enough that this
 > might be an issue.
 > 
 > Sorry for any confusion I may have caused.

Not at all.  It gave me an excuse to bug Alexander for some state-of-art 
details, to which he responded magnificently :)

Thankyou both, and Ari for entertaining such sport at his expense ..

cheers, Ian