From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750881AbXCYTX3 (ORCPT ); Sun, 25 Mar 2007 15:23:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752094AbXCYTX3 (ORCPT ); Sun, 25 Mar 2007 15:23:29 -0400 Received: from rgminet01.oracle.com ([148.87.113.118]:50796 "EHLO rgminet01.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750881AbXCYTX2 (ORCPT ); Sun, 25 Mar 2007 15:23:28 -0400 Date: Sun, 25 Mar 2007 12:23:51 -0700 From: Randy Dunlap To: Wink Saville Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3] Documention for trace records (trec). Message-Id: <20070325122351.6ce69dfd.randy.dunlap@oracle.com> In-Reply-To: <11747802992043-git-send-email-wink@saville.com> References: <11747802992043-git-send-email-wink@saville.com> Organization: Oracle Linux Eng. X-Mailer: Sylpheed 2.3.1 (GTK+ 2.8.10; x86_64-unknown-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Brightmail-Tracker: AAAAAQAAAAI= X-Brightmail-Tracker: AAAAAQAAAAI= X-Whitelist: TRUE X-Whitelist: TRUE Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 24 Mar 2007 16:51:37 -0700 Wink Saville wrote: > Trec is a light weight tracing mechanism that places > trace information into a buffer. The contents of the > buffer is dumped when errors occurs or when enabled > via SYSRQ commands. > > Signed-off-by: Wink Saville > --- > Documentation/trec.txt | 87 ++++++++++++++++++++++++++++++++++++++++++++++++ > 1 files changed, 87 insertions(+), 0 deletions(-) > create mode 100644 Documentation/trec.txt > > diff --git a/Documentation/trec.txt b/Documentation/trec.txt > new file mode 100644 > index 0000000..2275edd > --- /dev/null > +++ b/Documentation/trec.txt > @@ -0,0 +1,87 @@ > +Title : Trace Records > +Authors : Wink Saville > + > +CONTENTS > + > +1. Concepts > +2. Architectures Supported > +3. Configuring > +4. API Reference > +5. Overhead > +6. TODO > + > + > +1. Concepts > + > +Trace records are a light weight tracing technique that time stamps lightweight ... timestamps > +small amounts of information and stores them in a buffer. TREC's are > +light enough that they may be sprinkled most anywhere in the kernel > +and have very little performance impact. > + > +For instance they can be placed in the scheduler and ISR's to watch > +the interaction between ISR's and the scheduler. They can be placed > +in memory handling routines to determine how and when memory is > +allocated and freed. > + > +In the current default configuration the trec's are dumped by calling > +trec_print_snapshot when die() or panic() are called as well as when is > +the kernel itself page faults in do_page_fault. > + > +If CONFIG_MAGIC_SYSRQ is the 'y' command will execute trec_snapshot ^ enabled, > +and the 'z' command will print the current snapshot. > + > +A general macro TREC allows trec_write to be invoked as a macro and > +TRECC allows it to be invoked conditionally. See include/linux/trec.h > +for the current set of macros. > + > +2. Architectures Supported > + > +Should support all architectures has been tested only on: ^ ; > + > +- X86_64 > + > + > +3. Configuring > + > +Since trec's are implemented as a device driver they are configured > +by enabling support in the "Device Drivers" section of as they could ^ ?? > +be used early being a module is not supported. > + > + > +4. API Reference > + > +Trec supports the following API: > + > +void trec_init(void): > + > + Initialize the module, this may be called before the driver is loaded ^ ; (or maybe :) > + if it is desired to use trec's early. > + > +void trec_write(unsigned long pc, int pid, unsigned long v1, unsigned long v2); > + > + This is the routine used to write into the buffer. pc is the program counter end above line with , > + pid is the process id and v1 and v2 are two parameters. > + > +void trec_snapshot(void); > + > + Calling this function takes a snapshot of the current trec buffer so that it > + will not be modified. This is called prior to printing the snapshot via > + trec_print_snapshot. > + > +void trec_print_snapshot(void); > + > + Print the snapshot. > + > +5. Overhead > + > +Measured on a 2.4GHZ Core 2 Duo the readings between two TREC's is > +270 tics of the rdtsc or about 0.1us. No attempt has been made to > +optimize and less information can be collected if the overhead > +is still to high. too > + > + > +6. TODO > + > +a. Add code to dump trec to user space > +b. Enhance to allow runtime registration and runtime enable disable. > + --- ~Randy *** Remember to use Documentation/SubmitChecklist when testing your code ***