Re: More weird latency trace output (was Re: 2.6.17-rt1)

[Lee Revell]

On Thu, 2006-06-22 at 21:24 -0400, Lee Revell wrote:
> On Wed, 2006-06-21 at 22:51 -0400, Lee Revell wrote:
> > How can the latency tracer be reporting 1898us max latency while the
> > trace is of a 12us latency?  This must be a bug, correct?
> 
> I've found the bug.  The latency tracer uses get_cycles() for
> timestamping, which uses rdtsc, which is unusable for timing on dual
> core AMD64 machines due to the well known "unsynced TSCs" hardware bug.
> 
> Would a patch to convert the latency tracer to use gettimeofday() be
> acceptable?

OK, I tried that and it oopses on boot - presumably the latency tracer
runs before clocksource infrastructure is initialized.

Does anyone have any suggestions at all as to what a proper solution
would look like?  Is no one interested in this problem?

Lee

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