[Beowulf] IEEE 1588 (PTP) - a better cluster clock?

Patrick Ohly patrick.ohly at intel.com
Tue Jul 24 10:37:16 EDT 2007


On Tue, 2007-07-24 at 15:15 +0100, Ashley Pittman wrote:
[examples for the need of a more accurate clock]
> But none of the ones you list are more than vaguely related to HPC.
[...]
> The only thing I've found ntp to be lacking in is the ability to
> compile
> complex software over NFS on 2.6 kernels which have 64 bit timestamps,

So you haven't used MPI tracing tools yet? This is very much HPC
related. NTP is not good enough for that purpose, nor is a simple linear
clock correction. One of the artifacts you get in the trace when the
clocks of different processes are shifted against each other by more
than the latency of short messages are "backwards" messages which are
said to be received earlier than they were sent. Less obvious, but just
as inaccurate are shifts in the other direction.

-- 
Best Regards, Patrick Ohly

The content of this message is my personal opinion only and although
I am an employee of Intel, the statements I make here in no way
represent Intel's position on the issue, nor am I authorized to speak
on behalf of Intel on this matter.
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