From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751437AbeDDI2s (ORCPT ); Wed, 4 Apr 2018 04:28:48 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:60014 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751314AbeDDI2o (ORCPT ); Wed, 4 Apr 2018 04:28:44 -0400 From: Ravi Bangoria To: mhiramat@kernel.org, oleg@redhat.com, peterz@infradead.org, srikar@linux.vnet.ibm.com, rostedt@goodmis.org Cc: acme@kernel.org, ananth@linux.vnet.ibm.com, akpm@linux-foundation.org, alexander.shishkin@linux.intel.com, alexis.berlemont@gmail.com, corbet@lwn.net, dan.j.williams@intel.com, jolsa@redhat.com, kan.liang@intel.com, kjlx@templeofstupid.com, kstewart@linuxfoundation.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, milian.wolff@kdab.com, mingo@redhat.com, namhyung@kernel.org, naveen.n.rao@linux.vnet.ibm.com, pc@us.ibm.com, tglx@linutronix.de, yao.jin@linux.intel.com, fengguang.wu@intel.com, jglisse@redhat.com, Ravi Bangoria Subject: [PATCH v2 0/9] trace_uprobe: Support SDT markers having reference count (semaphore) Date: Wed, 4 Apr 2018 14:01:01 +0530 X-Mailer: git-send-email 2.14.3 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 x-cbid: 18040408-0040-0000-0000-0000042A3EC4 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18040408-0041-0000-0000-0000262D6F75 Message-Id: <20180404083110.18647-1-ravi.bangoria@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-04-04_02:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1804040089 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Userspace Statically Defined Tracepoints[1] are dtrace style markers inside userspace applications. Applications like PostgreSQL, MySQL, Pthread, Perl, Python, Java, Ruby, Node.js, libvirt, QEMU, glib etc have these markers embedded in them. These markers are added by developer at important places in the code. Each marker source expands to a single nop instruction in the compiled code but there may be additional overhead for computing the marker arguments which expands to couple of instructions. In case the overhead is more, execution of it can be omitted by runtime if() condition when no one is tracing on the marker: if (reference_counter > 0) { Execute marker instructions; } Default value of reference counter is 0. Tracer has to increment the reference counter before tracing on a marker and decrement it when done with the tracing. Currently, perf tool has limited supports for SDT markers. I.e. it can not trace markers surrounded by reference counter. Also, it's not easy to add reference counter logic in userspace tool like perf, so basic idea for this patchset is to add reference counter logic in the trace_uprobe infrastructure. Ex,[2] # cat tick.c ... for (i = 0; i < 100; i++) { DTRACE_PROBE1(tick, loop1, i); if (TICK_LOOP2_ENABLED()) { DTRACE_PROBE1(tick, loop2, i); } printf("hi: %d\n", i); sleep(1); } ... Here tick:loop1 is marker without reference counter where as tick:loop2 is surrounded by reference counter condition. # perf buildid-cache --add /tmp/tick # perf probe sdt_tick:loop1 # perf probe sdt_tick:loop2 # perf stat -e sdt_tick:loop1,sdt_tick:loop2 -- /tmp/tick hi: 0 hi: 1 hi: 2 ^C Performance counter stats for '/tmp/tick': 3 sdt_tick:loop1 0 sdt_tick:loop2 2.747086086 seconds time elapsed Perf failed to record data for tick:loop2. Same experiment with this patch series: # ./perf buildid-cache --add /tmp/tick # ./perf probe sdt_tick:loop2 # ./perf stat -e sdt_tick:loop2 /tmp/tick hi: 0 hi: 1 hi: 2 ^C Performance counter stats for '/tmp/tick': 3 sdt_tick:loop2 2.561851452 seconds time elapsed Note: - 'reference counter' is called as 'semaphore' in original Dtrace (or Systemtap, bcc and even in ELF) documentation and code. But the term 'semaphore' is misleading in this context. This is just a counter used to hold number of tracers tracing on a marker. This is not really used for any synchronization. So we are referring it as 'reference counter' in kernel / perf code. v2 changes: - [PATCH v2 3/9] is new. build_map_info() has a side effect. One has to perform mmput() when he is done with the mm. Let free_map_info() take care of mmput() so that one does not need to worry about it. - [PATCH v2 6/9] sdt_update_ref_ctr(). No need to use memcpy(). Reference counter can be directly updated using normal assignment. - [PATCH v2 6/9] Check valid vma is returned by sdt_find_vma() before incrementing / decrementing a reference counter. - [PATCH v2 6/9] Introduce utility functions for taking write lock on dup_mmap_sem. Use these functions in trace_uprobe to avoide race with fork / dup_mmap(). - [PATCH v2 6/9] Don't check presence of mm in tu->sml at decrement time. Purpose of maintaining the list is to ensure increment happen only once for each {trace_uprobe,mm} tuple. - [PATCH v2 7/9] v1 was not removing mm from tu->sml when process exits and tracing is still on. This leads to a problem if same address gets used by new mm. Use mmu_notifier to remove such mm from the list. This guarantees that all mm which has been added to tu->sml will be removed from list either when tracing ends or when process goes away. - [PATCH v2 7/9] Patch description was misleading. Change it. Add more generic python example. - [PATCH v2 7/9] Convert sml_rw_sem into mutex sml_lock. - [PATCH v2 7/9] Use builtin linked list in sdt_mm_list instead of defining it's own pointer chain. - Change the order of last two patches. - [PATCH v2 9/9] Check availability of ref_ctr_offset support by trace_uprobe infrastructure before using it. This ensures newer perf tool will still work on older kernels which does not support trace_uprobe with reference counter. - Other changes as suggested by Masami, Oleg and Steve. v1 can be found at: https://lkml.org/lkml/2018/3/13/432 [1] https://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation [2] https://github.com/iovisor/bcc/issues/327#issuecomment-200576506 [3] https://lkml.org/lkml/2017/12/6/976 Oleg Nesterov (1): Uprobe: Move mmput() into free_map_info() Ravi Bangoria (8): Uprobe: Export vaddr <-> offset conversion functions mm: Prefix vma_ to vaddr_to_offset() and offset_to_vaddr() Uprobe: Rename map_info to uprobe_map_info Uprobe: Export uprobe_map_info along with uprobe_{build/free}_map_info() trace_uprobe: Support SDT markers having reference count (semaphore) trace_uprobe/sdt: Fix multiple update of same reference counter trace_uprobe/sdt: Document about reference counter perf probe: Support SDT markers having reference counter (semaphore) Documentation/trace/uprobetracer.txt | 16 ++- include/linux/mm.h | 12 ++ include/linux/uprobes.h | 19 +++ kernel/events/uprobes.c | 79 ++++++----- kernel/trace/trace.c | 2 +- kernel/trace/trace_uprobe.c | 261 ++++++++++++++++++++++++++++++++++- tools/perf/util/probe-event.c | 18 ++- tools/perf/util/probe-event.h | 1 + tools/perf/util/probe-file.c | 34 ++++- tools/perf/util/probe-file.h | 1 + tools/perf/util/symbol-elf.c | 46 ++++-- tools/perf/util/symbol.h | 7 + 12 files changed, 431 insertions(+), 65 deletions(-) -- 1.8.3.1