Re: Microsecond accuracy

Maciej W. Rozycki
2000-12-07T16:42:44Z

On 7 Dec 2000, H. Peter Anvin wrote:

> Unfortunately the most important instance of the in-kernel flag -- the
> global one in the somewhat misnamed boot_cpu_data.x86_features --
> isn't actually readable in the /proc/cpuinfo file. It is perfectly
> possible (e.g. the "notsc" option) for ALL the CPUs to report this
> capability, but the global capability to still be off.

Hmm, I recall I implemented and explicitly verified switching the
/proc/cpuinfo "tsc" flag (as well as the userland access to the TSC) off
when I wrote the code to handle the "notsc" option. Has it changed since
then? I recall you modified the code a bit -- I looked at the changes
then but I was pretty confident the semantics was preserved.

There is no possibility to have TSC and non-TSC chips mixed in a single
SMP system (due to existing hardware, even though it's possible in
theory), so there is no problem with such an assymetry. Either all chips
have the "tsc" flag in /proc/cpuinfo on or off.

--
+ Maciej W. Rozycki, Technical University of Gdansk, Poland +
+--------------------------------------------------------------+
+ e-mail: macro@ds2.pg.gda.pl, PGP key available +