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Subject: Re: More weird latency trace output (was Re: 2.6.17-rt1)
From: Lee Revell <rlrevell@joe-job.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
       Steven Rostedt <rostedt@goodmis.org>
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Date: Thu, 22 Jun 2006 21:24:52 -0400
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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?

Lee