From patchwork Thu Jun 16 08:44:58 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Daniel Bristot de Oliveira X-Patchwork-Id: 12883565 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 DC68DC43334 for ; Thu, 16 Jun 2022 08:47:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1376263AbiFPIrS (ORCPT ); Thu, 16 Jun 2022 04:47:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36558 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1376264AbiFPIqx (ORCPT ); Thu, 16 Jun 2022 04:46:53 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2F9595DD39; Thu, 16 Jun 2022 01:46:31 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id ECA5461D74; Thu, 16 Jun 2022 08:46:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 24486C385A2; Thu, 16 Jun 2022 08:46:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1655369190; bh=r3LQRxsB4zvMJAbVYAKgMVYZMxuBkCguR2Xd1O6Gqto=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ZQpUvZVMbha3cDI+oZladehpZNwnxt/I10aiGs74dcvV7UO3yi9Uty8Oqa4mnGeNS 52KIYOkQ8WjNXY3FwMYqU+RP0f1PzANjDe7pJTn/J/aqCEAcBUU7qBj+xUsA6Lc69J uJ5U8Eu38vYK6aR0X0cLFHl3noTa82euSfsWBofFWWAOW0t/pFfhIEzrlqnw3YIxVG MIZCzoKO+jJ9UGe4XjCnTy+si8pNFzZU91MuoBdUcksM4MWrCqum8mbghUCy7mpE/3 YQxhti9YnXzZXWNBJUlCk8mO6GusqoQD8K87KNDJw3TnZU0lwrN2t6knndqsI9AksG dJT6YTpoOOyMw== From: Daniel Bristot de Oliveira To: Steven Rostedt Cc: Daniel Bristot de Oliveira , Wim Van Sebroeck , Guenter Roeck , Jonathan Corbet , Ingo Molnar , Thomas Gleixner , Peter Zijlstra , Will Deacon , Catalin Marinas , Marco Elver , Dmitry Vyukov , "Paul E. McKenney" , Shuah Khan , Gabriele Paoloni , Juri Lelli , Clark Williams , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-devel@vger.kernel.org Subject: [PATCH V4 16/20] Documentation/rv: Add deterministic automata instrumentation documentation Date: Thu, 16 Jun 2022 10:44:58 +0200 Message-Id: <30171062e035a5cf0e64cfa9cbb8e56376ec5101.1655368610.git.bristot@kernel.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-trace-devel@vger.kernel.org Add the da_monitor_instrumentation.rst. It describes the basics of RV monitor instrumentation. Cc: Wim Van Sebroeck Cc: Guenter Roeck Cc: Jonathan Corbet Cc: Steven Rostedt Cc: Ingo Molnar Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Will Deacon Cc: Catalin Marinas Cc: Marco Elver Cc: Dmitry Vyukov Cc: "Paul E. McKenney" Cc: Shuah Khan Cc: Gabriele Paoloni Cc: Juri Lelli Cc: Clark Williams Cc: linux-doc@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-trace-devel@vger.kernel.org Signed-off-by: Daniel Bristot de Oliveira --- .../trace/rv/da_monitor_instrumentation.rst | 223 ++++++++++++++++++ 1 file changed, 223 insertions(+) create mode 100644 Documentation/trace/rv/da_monitor_instrumentation.rst diff --git a/Documentation/trace/rv/da_monitor_instrumentation.rst b/Documentation/trace/rv/da_monitor_instrumentation.rst new file mode 100644 index 000000000000..994110050d93 --- /dev/null +++ b/Documentation/trace/rv/da_monitor_instrumentation.rst @@ -0,0 +1,223 @@ +Deterministic Automata Instrumentation +======================================== + +This document introduces some concepts behind the **Deterministic Automata +(DA)** monitor instrumentation. + +The synthesis of automata-based models into the Linux *RV monitor* abstraction +is automated by a tool named dot2k, and the "rv/da_monitor.h" provided +by the RV interface. + +For example, given a file "wip.dot", representing a per-cpu monitor, with +this content:: + + digraph state_automaton { + center = true; + size = "7,11"; + rankdir = LR; + {node [shape = circle] "non_preemptive"}; + {node [shape = plaintext, style=invis, label=""] "__init_preemptive"}; + {node [shape = doublecircle] "preemptive"}; + {node [shape = circle] "preemptive"}; + "__init_preemptive" -> "preemptive"; + "non_preemptive" [label = "non_preemptive"]; + "non_preemptive" -> "non_preemptive" [ label = "sched_waking" ]; + "non_preemptive" -> "preemptive" [ label = "preempt_enable" ]; + "preemptive" [label = "preemptive"]; + "preemptive" -> "non_preemptive" [ label = "preempt_disable" ]; + { rank = min ; + "__init_preemptive"; + "preemptive"; + } + } + +That is the "DOT" representation of this automata model:: + + preempt_enable + +---------------------------------+ + v | + #============# preempt_disable +------------------+ + --> H preemptive H -----------------> | non_preemptive | + #============# +------------------+ + ^ sched_waking | + +--------------+ + + +Run the dot2k tool with the model, specifying that it is a "per-cpu" +model:: + + $ dot2k -d ~/wip.dot -t per_cpu + +This will create a directory named "wip/" with the following files: + +- model.h: the wip in C +- wip.h: tracepoints that report the execution of the events by the + monitor +- wip.c: the RV monitor + +The monitor instrumentation should be done entirely in the RV monitor, +in the example above, in the wip.c file. + +The RV monitor instrumentation section +-------------------------------------- + +The RV monitor file created by dot2k, with the name "$MODEL_NAME.c" +will include a section dedicated to instrumentation. + +In the example of the wip.dot above, it will look like:: + + /* + * This is the instrumentation part of the monitor. + * + * This is the section where manual work is required. Here the kernel events + * are translated into model's event. + * + */ + static void handle_preempt_disable(void *data, /* XXX: fill header */) + { + da_handle_event_wip(preempt_disable_wip); + } + + static void handle_preempt_enable(void *data, /* XXX: fill header */) + { + da_handle_event_wip(preempt_enable_wip); + } + + static void handle_sched_waking(void *data, /* XXX: fill header */) + { + da_handle_event_wip(sched_waking_wip); + } + + static int start_wip(void) + { + int retval; + + retval = da_monitor_init_wip(); + if (retval) + return retval; + + rv_attach_trace_probe("wip", /* XXX: tracepoint */, handle_preempt_disable); + rv_attach_trace_probe("wip", /* XXX: tracepoint */, handle_preempt_enable); + rv_attach_trace_probe("wip", /* XXX: tracepoint */, handle_sched_waking); + + return 0; + } + +The comment at the top of the section explains the general idea: the +instrumentation section translates *kernel events* into the *events +accepted by the model*. + +Tracing callback functions +----------------------------- + +The first three functions are skeletons for callback *handler functions* for +each of the three events from the wip model. The developer does not +necessarily need to use them: they are just starting points. + +Using the example of:: + + void handle_preempt_disable(void *data, /* XXX: fill header */) + { + da_handle_event_wip(preempt_disable_wip); + } + +The "preempt_disable" event from the model conects directly to the +"preemptirq:preempt_disable". The "preemptirq:preempt_disable" event +has the following signature, from "include/trace/events/preemptirq.h":: + + TP_PROTO(unsigned long ip, unsigned long parent_ip) + +Hence, the "handle_preempt_disable()" function will look like:: + + void handle_preempt_disable(void *data, unsigned long ip, unsigned long parent_ip) + +In this case, the kernel even translates one to one with the automata event, +and indeed, no other change is needed for this function. + +The next handler function, "handle_preempt_enable()" has the same argument +list from the "handle_preempt_disable()". The difference is that the +"preempt_enable" event will be used to synchronize the system to the model. + +Initially, the *model* is placed in the initial state. However, the *system* +might, or might not be in the initial state. The monitor cannot start +processing events until it knows that the system reached the initial state. +Otherwise the monitor and the system could be out-of-sync. + +Looking at the automata definition, it is possible to see that the system +and the model are expected to return to the initial state after the +"preempt_enable" execution. Hence, it can be used to synchronize the +system and the model at the initialization of the monitoring section. + +The initialization is informed via an special handle function, the +"da_handle_init_event_$(MONITOR)(event)", in this case:: + + da_handle_event_wip(preempt_disable_wip); + +So, the callback function will look like:: + + void handle_preempt_enable(void *data, unsigned long ip, unsigned long parent_ip) + { + da_handle_init_event_wip(preempt_enable_wip); + } + +Finally, the "handle_sched_waking()" will look like:: + + void handle_sched_waking(void *data, struct task_struct *task) + { + da_handle_event_wip(sched_waking_wip); + } + +And the explanation is left for the reader as an exercise. + +Start and Stop functions +------------------------ + +dot2k automatically creates two special functions:: + + start_$MODELNAME() + stop_$MODELNAME() + +These functions are called when the monitor is enabled and disabled, +respectivelly. + +They should be used to *attach* and *detach* the instrumentation to the running +system. The developer must add to the relative function all that is needed to +*attach* and *detach* its monitor to the system. + +For the wip case, these functions were named:: + + start_wip() + stop_wip() + +But no change was required because: by default, these functions *attach* and +*detach* the tracepoints_to_attach, which was enough for this case. + +Instrumentation helpers +-------------------------- + +To complete the instrumentation, the *handler functions* need to be attached to a +kernel event, at the monitoring start phase. + +The RV interface also facilitates this step. For example, the macro "rv_attach_trace_probe()" +is used to connect the wip model events to the relative kernel event. dot2k automatically +adds "rv_attach_trace_probe()" function call for each model event in the start phase, as +a suggestion. + +For example, from the wip sample model:: + + static int start_wip(void) + { + int retval; + + retval = da_monitor_init_wip(); + if (retval) + return retval; + + rv_attach_trace_probe("wip", /* XXX: tracepoint */, handle_preempt_disable); + rv_attach_trace_probe("wip", /* XXX: tracepoint */, handle_preempt_enable); + rv_attach_trace_probe("wip", /* XXX: tracepoint */, handle_sched_waking); + + return 0; + } + +The probes then need to be detached at the stop phase.