From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 6881 invoked by alias); 20 Feb 2012 06:00:05 -0000 Received: (qmail 6734 invoked by uid 22791); 20 Feb 2012 06:00:02 -0000 X-SWARE-Spam-Status: No, hits=-2.8 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00 X-Spam-Check-By: sourceware.org Received: from localhost (HELO sourceware.org) (127.0.0.1) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Mon, 20 Feb 2012 05:59:49 +0000 From: "brendan.gregg at joyent dot com" To: systemtap@sourceware.org Subject: [Bug documentation/13713] New: MAXTRACE/MAXBACKTRACE undocumented feature Date: Mon, 20 Feb 2012 06:00:00 -0000 X-Bugzilla-Reason: AssignedTo X-Bugzilla-Type: new X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: systemtap X-Bugzilla-Component: documentation X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: brendan.gregg at joyent dot com X-Bugzilla-Status: NEW X-Bugzilla-Priority: P2 X-Bugzilla-Assigned-To: systemtap at sourceware dot org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Changed-Fields: Message-ID: X-Bugzilla-URL: http://sourceware.org/bugzilla/ Auto-Submitted: auto-generated Content-Type: text/plain; charset="UTF-8" MIME-Version: 1.0 Mailing-List: contact systemtap-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Post: List-Help: , Sender: systemtap-owner@sourceware.org X-SW-Source: 2012-q1/txt/msg00155.txt.bz2 http://sourceware.org/bugzilla/show_bug.cgi?id=13713 Bug #: 13713 Summary: MAXTRACE/MAXBACKTRACE undocumented feature Product: systemtap Version: unspecified Status: NEW Severity: normal Priority: P2 Component: documentation AssignedTo: systemtap@sourceware.org ReportedBy: brendan.gregg@joyent.com Classification: Unclassified I was to file a bug about backtrace() being truncated to 20 entries (21, including the current function), but after some digging realized that this can be tuned - it's just not in the documentation. MAXTRACE - number of stack frames - can be increased to trace stack back traces longer than 20. If it helps, here is an example of a long stack (after increasing MAXTRACE): 0xffffffffa003f009 : tcp_packet+0x29/0x14e0 [nf_conntrack] 0xffffffffa003a72b : nf_conntrack_in+0x3bb/0xaf0 [nf_conntrack] 0xffffffffa0058691 : ipv4_conntrack_in+0x21/0x30 [nf_conntrack_ipv4] 0xffffffff814fdfb5 : nf_iterate+0x85/0xc0 [kernel] 0xffffffff814fe065 : nf_hook_slow+0x75/0x150 [kernel] 0xffffffff81508a44 : ip_rcv+0x224/0x300 [kernel] 0xffffffff814d2633 : __netif_receive_skb+0x523/0x5c0 [kernel] 0xffffffff814d3230 : netif_receive_skb+0x80/0x90 [kernel] 0xffffffffa001fe69 : virtnet_poll+0x5c9/0x830 [virtio_net] 0xffffffff814d3a7b : net_rx_action+0x12b/0x270 [kernel] 0xffffffff81075378 : __do_softirq+0xb8/0x230 [kernel] 0xffffffff815ebbec : call_softirq+0x1c/0x30 [kernel] 0xffffffff81016275 : do_softirq+0x65/0xa0 [kernel] 0xffffffff810748e4 : local_bh_enable+0x94/0xa0 [kernel] 0xffffffff814d4f02 : dev_queue_xmit+0x1c2/0x600 [kernel] 0xffffffff8150d10b : ip_finish_output+0x16b/0x2f0 [kernel] 0xffffffff8150dc68 : ip_output+0x98/0xa0 [kernel] 0xffffffff8150d369 : ip_local_out+0x29/0x30 [kernel] 0xffffffff8150d4bf : ip_queue_xmit+0x14f/0x3f0 [kernel] 0xffffffff815248f4 : tcp_transmit_skb+0x3e4/0x8d0 [kernel] 0xffffffff81525447 : tcp_write_xmit+0xf7/0xa20 [kernel] 0xffffffff81525da0 : tcp_push_one+0x30/0x40 [kernel] 0xffffffff81517635 : tcp_sendmsg+0xcb5/0xd90 [kernel] 0xffffffff8153c7e4 : inet_sendmsg+0x64/0xb0 [kernel] 0xffffffff814bb39a : sock_aio_write+0x13a/0x160 [kernel] 0xffffffff811786c2 : do_sync_write+0xd2/0x110 [kernel] 0xffffffff8117905d : vfs_write+0x16d/0x180 [kernel] 0xffffffff811792ca : sys_write+0x4a/0x90 [kernel] 0xffffffff815e9982 : system_call_fastpath+0x16/0x1b [kernel] Without increasing MAXTRACE, this is truncated. If this is the correct tunable, its existence can be added to the function::backtrace man page (which currently just has MAXSTRINGLEN). 20 frames is often enough, but sometimes isn't. There is another tunable, MAXBACKTRACE (set to 20), which can't be redefined using -D. It didn't affect the stack length when I tried tuning it on my system, but it looks related, so may need to in some situations. If it matters, I was testing on: # stap -V Systemtap translator/driver (version 1.6/0.152 non-git sources) Copyright (C) 2005-2011 Red Hat, Inc. and others This is free software; see the source for copying conditions. enabled features: AVAHI LIBRPM LIBSQLITE3 NSS BOOST_SHARED_PTR TR1_UNORDERED_MAP NLS # uname -a Linux 9d219ce8-cf52-409f-a14a-b210850f3231 3.2.6-3.fc16.x86_64 #1 SMP Mon Feb 13 20:35:42 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux # cat /etc/redhat-release Fedora release 16 (Verne) This is Fedora as a guest running under KVM. SystemTap was installed via yum. -- Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are the assignee for the bug.