Re: [PATCH] hp-timing for ppc32/64

[Steve Munroe <sjmunroe at us dot ibm dot com>]

libc-alpha-owner@sources.redhat.com wrote on 10/11/2005 07:11:30 PM:

> On Mon, 2005-10-10 at 17:18 -0500, Steve Munroe wrote:
> 
> > This patch adds hp-timing for powerpc32 and powerpc64.
> 
> A couple of questions here:
> 
>  - Do you have any provision to deal with ppc32 CPUs that do not provide
> the TB but different timing mecanisms ? Should we add a CPU feature bit
> exposed by the kernel to userland ?
> 
Which CPUs don't implement the timebase. It is a required element of the 
PowerPC architecture (not optional).

>  - I haven't read/found the hp-timing spec yet, but are we supposed to
> be able to convert between hp-timing values/diffs & actual time units
> (like nanoseconds or so) ? That would require to know the TB calibration
> values, which is currently not exposed by the kernel in any way you are
> supposed to use in userland afaik. I could add a vDSO entry point for
> that though (and to a ppc32 vDSO which will happen soon).
> 

hp-timing returns the raw timebase which is analogous to the Intel "Time 
Stamp Counter". There is no requirement convert to clock time or 
nanoseconds. This is used for internal timing of the loader and internal 
libc test.

However clock_gettime(CLOCK_PROCESS_CPUTIME_ID) may use hp-timing if 
__get_clockfreq() is available. The other implementations read and parse 
/proc/cpuinfo. But it would be useful to get the timebase value directly 
from vdso instead!

Steven J. Munroe
Linux on Power Toolchain Architect
IBM Corporation, Linux Technology Center