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From: "T. Smith" <tlsmith3777@gmail.com>
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Subject: runaway latency detection
Message-Id: <94710CE6-857F-424A-9D50-8569D6282367@gmail.com>
Date: Sat, 20 Aug 2016 12:03:37 -0500
Cc: linux-kernel@vger.kernel.org
To: Daniel Bristot de Oliveira <bristot@redhat.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
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Trying to isolate PREEMPT_RT (full preemption) runaway latency conditions seen when using the cyclictest on the 4.1.8 SMP PREEMPT_RT kernel.  Seen average latency of 3uS, but runaway or outlier max latency seems indeterminate.  Noted 72uS with one run of the cyclictest for example. Is this a known issue, the cause understood, and is there a patch for this?  

The goal is to isolate causes of indeterminism when using the PREEMPT_RT kernel configuration with full preemption and to characterize latency and jitter using ftrace, any recommendations?