From patchwork Mon Mar 20 13:16:50 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: pengdonglin X-Patchwork-Id: 13181217 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5ED1DC6FD1D for ; Mon, 20 Mar 2023 13:18:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231795AbjCTNSW (ORCPT ); Mon, 20 Mar 2023 09:18:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42228 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231775AbjCTNSK (ORCPT ); Mon, 20 Mar 2023 09:18:10 -0400 Received: from mail-m118111.qiye.163.com (mail-m118111.qiye.163.com [115.236.118.111]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 88C8723869; Mon, 20 Mar 2023 06:17:52 -0700 (PDT) Received: from localhost.localdomain (unknown [117.133.56.22]) by mail-m118111.qiye.163.com (Hmail) with ESMTPA id 427315801C3; Mon, 20 Mar 2023 21:17:38 +0800 (CST) From: Donglin Peng To: mhiramat@kernel.org, rostedt@goodmis.org, linux@armlinux.org.uk, mark.rutland@arm.com, will@kernel.org, catalin.marinas@arm.com, palmer@dabbelt.com, paul.walmsley@sifive.com, tglx@linutronix.de, dave.hansen@linux.intel.com, x86@kernel.org, mingo@redhat.com, xiehuan09@gmail.com, dinghui@sangfor.com.cn, huangcun@sangfor.com.cn, dolinux.peng@gmail.com Cc: linux-trace-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Donglin Peng Subject: [PATCH v5 2/2] tracing: Add documentation for funcgraph-retval and graph_retval_hex Date: Mon, 20 Mar 2023 06:16:50 -0700 Message-Id: <20230320131650.482594-3-pengdonglin@sangfor.com.cn> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230320131650.482594-1-pengdonglin@sangfor.com.cn> References: <20230320131650.482594-1-pengdonglin@sangfor.com.cn> MIME-Version: 1.0 X-HM-Spam-Status: e1kfGhgUHx5ZQUpXWQgPGg8OCBgUHx5ZQUlOS1dZFg8aDwILHllBWSg2Ly tZV1koWUFITzdXWS1ZQUlXWQ8JGhUIEh9ZQVkZS0hMVk4YSEgdTE8dHU0dGlUTARMWGhIXJBQOD1 lXWRgSC1lBWUpKTFVKSEhVTk1VSUlZV1kWGg8SFR0UWUFZT0tIVUpISkJIT1VKS0tVS1kG X-HM-Sender-Digest: e1kMHhlZQR0aFwgeV1kSHx4VD1lBWUc6NQw6SDo4DD0VPRFJThQ8GAs# NzpPCzBVSlVKTUxCSEpDSU5CT0NNVTMWGhIXVQseFRwfFBUcFxIVOwgaFRwdFAlVGBQWVRgVRVlX WRILWUFZSkpMVUpISFVOTVVJSVlXWQgBWUFMS0pONwY+ X-HM-Tid: 0a86ff2b15712eb7kusn427315801c3 X-HM-MType: 1 Precedence: bulk List-ID: X-Mailing-List: linux-trace-kernel@vger.kernel.org Add documentation for the two newly introduced options for the function_graph tracer. The new option funcgraph-retval is used to control whether or not to display the return value. The new option graph_retval_hex is used to control the display format of the return value. Signed-off-by: Donglin Peng --- v5: - Describe the limitations of funcgraph-retval --- Documentation/trace/ftrace.rst | 75 ++++++++++++++++++++++++++++++++++ 1 file changed, 75 insertions(+) diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst index b927fb2b94dc..797841d15da9 100644 --- a/Documentation/trace/ftrace.rst +++ b/Documentation/trace/ftrace.rst @@ -1328,6 +1328,19 @@ Options for function_graph tracer: only a closing curly bracket "}" is displayed for the return of a function. + funcgraph-retval + When set, the return event will include the function and + its return value. Note that even if the function return + type is void, a return value will also be printed, you + should ignore it. This option is off by default. + + graph_retval_hex + Depend on function-retval. When set, the function return + value will be printed in hexadecimal format. If this is not + set and the return value looks like an error code, it will + be printed in signed decimal format, else in hexadecimal + format. This option is off by default. + sleep-time When running function graph tracer, to include the time a task schedules out in its function. @@ -2673,6 +2686,68 @@ It is default disabled. 0) 1.757 us | } /* kmem_cache_free() */ 0) 2.861 us | } /* putname() */ +The return value of each traced function can be displayed. This +feature can be very useful when you encounter system call failures +and want to locate the function that return errors firstly. + + - hide: echo nofuncgraph-retval > trace_options + - show: echo funcgraph-retval > trace_options + + Example with funcgraph-retval:: + + 1) | cgroup_migrate() { + 1) 0.651 us | cgroup_migrate_add_task(); /* = 0xffff93fcfd346c00 */ + 1) | cgroup_migrate_execute() { + 1) | cpu_cgroup_can_attach() { + 1) | cgroup_taskset_first() { + 1) 0.732 us | cgroup_taskset_next(); /* = 0xffff93fc8fb20000 */ + 1) 1.232 us | } /* cgroup_taskset_first = 0xffff93fc8fb20000 */ + 1) 0.380 us | sched_rt_can_attach(); /* = 0x0 */ + 1) 2.335 us | } /* cpu_cgroup_can_attach = -22 */ + 1) 4.369 us | } /* cgroup_migrate_execute = -22 */ + 1) 7.143 us | } /* cgroup_migrate = -22 */ + +The above example shows that the cgroup function cpu_cgroup_can_attach +returned the error code -22 firstly, then we can read the code of this +function to get the root cause. + +If the option graph_retval_hex is not set and the return value looks +like an error code, it will be printed in signed decimal format. In +other cases, it will be printed in hexadecimal format. + + - hexadecimal or signed decimal: echo nograph_retval_hex > trace_options + - hexadecimal: echo graph_retval_hex > trace_options + + Example with graph_retval_hex:: + + 1) | cgroup_migrate() { + 1) 0.651 us | cgroup_migrate_add_task(); /* = 0xffff93fcfd346c00 */ + 1) | cgroup_migrate_execute() { + 1) | cpu_cgroup_can_attach() { + 1) | cgroup_taskset_first() { + 1) 0.732 us | cgroup_taskset_next(); /* = 0xffff93fc8fb20000 */ + 1) 1.232 us | } /* cgroup_taskset_first = 0xffff93fc8fb20000 */ + 1) 0.380 us | sched_rt_can_attach(); /* = 0x0 */ + 1) 2.335 us | } /* cpu_cgroup_can_attach = 0xffffffea */ + 1) 4.369 us | } /* cgroup_migrate_execute = 0xffffffea */ + 1) 7.143 us | } /* cgroup_migrate = 0xffffffea */ + +There are some limitations when using the funcgraph-retval currently: + +- Even if the function return type is void, a return value will still + be printed, and you can just ignore it. + +- Even if the return value is not an error code actually, it may be + displayed as an error code. You should read the code to check. + For example, both 0xfe and 0xfffe are be interpreted as -2. + +- Only the value of the first return register will be recorded and + printed even if the return values may be stored in two registers + actually. For example, both the eax and edx are used to store a + 64 bit return value in the x86 architecture, and the eax stores + the low 32 bit, the edx stores the high 32 bit, however only the + value stored in eax will be recorded and printed. + You can put some comments on specific functions by using trace_printk() For example, if you want to put a comment inside the __might_sleep() function, you just have to include