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

Patrick Geoffray patrick at myri.com
Fri Jul 20 16:07:09 EDT 2007


Hi Patrick,

Patrick Ohly wrote:
> That's all for now (and probably enough stuff, too ... although perhaps
> you prefer detailed emails over bullet items on a PowerPoint
> presentation). So what do you think?

Since you are asking, here is my personal opinion: I don't think there 
is a need for a system-wide PTP service. NTP's precision is good enough 
for comparing log and other administration needs. The only requirement 
for a high precision/high accuracy global clock reference that I would 
consider legitimate is for tracing tools (that's where you come from). 
In this case, why not running NTP as part of the tracing environment ?

You could say that it would be useful to factorize this functionality so 
that it can be shared by several tracing libraries. I don't think it's 
worth the effort, as one rarely uses two different tracing tool at the 
same time.

I don't know enough about PTP to comment on the implementation, except 
that relying on multicast is a bad, bad idea. It does not scale and it's 
very unreliable under load (induces contention if reliable).

Patrick
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