Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932978AbZAPLES (ORCPT ); Fri, 16 Jan 2009 06:04:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755324AbZAPLEB (ORCPT ); Fri, 16 Jan 2009 06:04:01 -0500 Received: from mga03.intel.com ([143.182.124.21]:62946 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751134AbZAPLD6 (ORCPT ); Fri, 16 Jan 2009 06:03:58 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.37,276,1231142400"; d="scan'208";a="100685824" Date: Fri, 16 Jan 2009 12:03:54 +0100 From: Markus Metzger To: linux-kernel@vger.kernel.org, mingo@elte.hu, tglx@linutronix.de, hpa@zytor.com Cc: markus.t.metzger@intel.com, markus.t.metzger@gmail.com, srostedt@redhat.com Subject: [patch 5/5] x86, ftrace, hw-branch-tracer: documentation Message-ID: <20090116120354.A30366@sedona.ch.intel.com> Mime-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.2.5i Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4864 Lines: 117 Document the hw-branch-tracer in the ftrace documentation. Signed-off-by: Markus Metzger --- Index: ftrace/Documentation/ftrace.txt =================================================================== --- ftrace.orig/Documentation/ftrace.txt 2008-12-11 11:23:48.000000000 +0100 +++ ftrace/Documentation/ftrace.txt 2009-01-16 10:58:07.000000000 +0100 @@ -165,6 +165,8 @@ nop - This is not a tracer. To remove all tracers from tracing simply echo "nop" into current_tracer. + hw-branch-tracer - traces branches on all cpu's in a circular buffer. + Examples of using the tracer ---------------------------- @@ -1152,6 +1154,78 @@ return 0; } + +hw-branch-tracer (x86 only) +--------------------------- + +This tracer uses the x86 last branch tracing hardware feature to +collect a branch trace on all cpus with relatively low overhead. + +The tracer uses a fixed-size circular buffer per cpu and only +traces ring 0 branches. The trace file dumps that buffer in the +following format: + +# tracer: hw-branch-tracer +# +# CPU# TO <- FROM + 0 scheduler_tick+0xb5/0x1bf <- task_tick_idle+0x5/0x6 + 2 run_posix_cpu_timers+0x2b/0x72a <- run_posix_cpu_timers+0x25/0x72a + 0 scheduler_tick+0x139/0x1bf <- scheduler_tick+0xed/0x1bf + 0 scheduler_tick+0x17c/0x1bf <- scheduler_tick+0x148/0x1bf + 2 run_posix_cpu_timers+0x9e/0x72a <- run_posix_cpu_timers+0x5e/0x72a + 0 scheduler_tick+0x1b6/0x1bf <- scheduler_tick+0x1aa/0x1bf + + +The tracer may be used to dump the trace for the oops'ing cpu on a +kernel oops into the system log. To enable this, ftrace_dump_on_oops +must be set. To set ftrace_dump_on_oops, one can either use the sysctl +function or set it via the proc system interface. + + sysctl kernel.ftrace_dump_on_oops=1 + +or + + echo 1 > /proc/sys/kernel/ftrace_dump_on_oops + + +Here's an example of such a dump after a null pointer dereference in a +kernel module: + +[57848.105921] BUG: unable to handle kernel NULL pointer dereference at 0000000000000000 +[57848.106019] IP: [] open+0x6/0x14 [oops] +[57848.106019] PGD 2354e9067 PUD 2375e7067 PMD 0 +[57848.106019] Oops: 0002 [#1] SMP +[57848.106019] last sysfs file: /sys/devices/pci0000:00/0000:00:1e.0/0000:20:05.0/local_cpus +[57848.106019] Dumping ftrace buffer: +[57848.106019] --------------------------------- +[...] +[57848.106019] 0 chrdev_open+0xe6/0x165 <- cdev_put+0x23/0x24 +[57848.106019] 0 chrdev_open+0x117/0x165 <- chrdev_open+0xfa/0x165 +[57848.106019] 0 chrdev_open+0x120/0x165 <- chrdev_open+0x11c/0x165 +[57848.106019] 0 chrdev_open+0x134/0x165 <- chrdev_open+0x12b/0x165 +[57848.106019] 0 open+0x0/0x14 [oops] <- chrdev_open+0x144/0x165 +[57848.106019] 0 page_fault+0x0/0x30 <- open+0x6/0x14 [oops] +[57848.106019] 0 error_entry+0x0/0x5b <- page_fault+0x4/0x30 +[57848.106019] 0 error_kernelspace+0x0/0x31 <- error_entry+0x59/0x5b +[57848.106019] 0 error_sti+0x0/0x1 <- error_kernelspace+0x2d/0x31 +[57848.106019] 0 page_fault+0x9/0x30 <- error_sti+0x0/0x1 +[57848.106019] 0 do_page_fault+0x0/0x881 <- page_fault+0x1a/0x30 +[...] +[57848.106019] 0 do_page_fault+0x66b/0x881 <- is_prefetch+0x1ee/0x1f2 +[57848.106019] 0 do_page_fault+0x6e0/0x881 <- do_page_fault+0x67a/0x881 +[57848.106019] 0 oops_begin+0x0/0x96 <- do_page_fault+0x6e0/0x881 +[57848.106019] 0 trace_hw_branch_oops+0x0/0x2d <- oops_begin+0x9/0x96 +[...] +[57848.106019] 0 ds_suspend_bts+0x2a/0xe3 <- ds_suspend_bts+0x1a/0xe3 +[57848.106019] --------------------------------- +[57848.106019] CPU 0 +[57848.106019] Modules linked in: oops +[57848.106019] Pid: 5542, comm: cat Tainted: G W 2.6.28 #23 +[57848.106019] RIP: 0010:[] [] open+0x6/0x14 [oops] +[57848.106019] RSP: 0018:ffff880235457d48 EFLAGS: 00010246 +[...] + + dynamic ftrace -------------- --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. 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