From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754340AbbDNC30 (ORCPT ); Mon, 13 Apr 2015 22:29:26 -0400 Received: from e31.co.us.ibm.com ([32.97.110.149]:43133 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753972AbbDNC3T (ORCPT ); Mon, 13 Apr 2015 22:29:19 -0400 Message-ID: <552C7B77.1000607@linux.vnet.ibm.com> Date: Mon, 13 Apr 2015 21:29:11 -0500 From: "Suresh E. Warrier" User-Agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: lklml CC: Steven Rostedt , Frederic Weisbecker , Ingo Molnar , Paul Mackerras Subject: [PATCH 0/2] ring-buffer: More precise timestamps for nested writes References: <1428459449-10664-1-git-send-email-warrier@linux.vnet.ibm.com> In-Reply-To: <1428459449-10664-1-git-send-email-warrier@linux.vnet.ibm.com> X-Forwarded-Message-Id: <1428459449-10664-1-git-send-email-warrier@linux.vnet.ibm.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15041402-8236-0000-0000-00000ABCDEA0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This patch set provides supports a way to record precise timestamps for nested writes and a tunable to enable the behavior. Nested writes occur when a trace writer is preempted, usually through an interrupt and the interrupt handler also writes its own trace. It has been noticed on large systems with lots of interrupts, several hundred trace events can be recorded with the same time stamp. Fixing this requires a small critical section in the trace write code in which interrupts are disabled. This is an expensive operation for many architectures. Hence, the need for a kernel tunable that allows the feature to be enabled by admins only when needed. Suresh Warrier (2): ring-buffer: Introduce precise nested timestamp sysfs attribute ring-buffer: More precise timestamps for nested writes Documentation/trace/ftrace.txt | 8 ++++ include/linux/ring_buffer.h | 9 +++++ kernel/trace/ring_buffer.c | 85 ++++++++++++++++++++++++++++++++++++++++-- kernel/trace/trace.c | 51 +++++++++++++++++++++++++ 4 files changed, 149 insertions(+), 4 deletions(-) -- 1.8.3.4