From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754073AbcHVCWm (ORCPT ); Sun, 21 Aug 2016 22:22:42 -0400 Received: from mail-oi0-f66.google.com ([209.85.218.66]:35343 "EHLO mail-oi0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753093AbcHVCWl (ORCPT ); Sun, 21 Aug 2016 22:22:41 -0400 Content-Type: text/plain; charset=us-ascii From: "T. Smith" Mime-Version: 1.0 (1.0) Message-Id: <8E6107F3-E531-44C2-85B8-C83A35C924DF@gmail.com> Date: Sun, 21 Aug 2016 21:22:37 -0500 X-Mailer: iPad Mail (13G35) Subject: runaway latency detection To: "linux-kernel@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "irqbalance@lists.infradead.org" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id u7M2Ml2f011642 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 random spikes seem 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? This is on ARM8 Cortex-A53 four core. Running the cyclictest on an isolated core 2 or 3 shows same behavior as do other platforms. No Trusted OS configured. 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 on catching random latency spikes using ftrace or profiling when running the cyclictest?