From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 37E1EC4360C for ; Tue, 8 Oct 2019 22:08:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0715921721 for ; Tue, 8 Oct 2019 22:08:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="apob5AbB" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727219AbfJHWIg (ORCPT ); Tue, 8 Oct 2019 18:08:36 -0400 Received: from mail-qk1-f194.google.com ([209.85.222.194]:34541 "EHLO mail-qk1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725848AbfJHWIf (ORCPT ); Tue, 8 Oct 2019 18:08:35 -0400 Received: by mail-qk1-f194.google.com with SMTP id q203so380877qke.1 for ; Tue, 08 Oct 2019 15:08:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=HmAnv2AMByGJTLMx+qaFli2c0QMCdv+/kYbiz4UgAmk=; b=apob5AbBipyRBd2op800GqI+J3geM97O9qUL8TEHFGjZQ9Ct9rSEd6RCPqXIw/B/6U +Fl2YtAzVwinPzdJhnroeou3OV5rfQxjmCrkyyu8bCiN+jYOX5TJMg7q5TPXUi8a39Qr k/iiFhxy7pjz4V2Vdxv2WhgPZvNcOmdlegmMCM1CRZCbq2NQjK9F710wB3Ybyk7emOGD j6VWMoGMomMn5GWlHfOvEIEmDzm8Lm5Vpr2b9LnhRmgU3VlGtKHoZ6zJKvI6yatVxoYs Sgv6NaMCi+xl4GmckZSckUOxoxp48poEdb/ymaLdXg0NoslTp6B/oK6DIZ+ee9s/xlE2 sdqQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=HmAnv2AMByGJTLMx+qaFli2c0QMCdv+/kYbiz4UgAmk=; b=iuisNwK6n33/YXRfM+5/y7LhM/yAeH/QqkBicSyar5axK1JO8JDfe9U2YObl3De4AN sAjL0QjZQd3H4MtyfrGfN/Q6pwSgpjwtHJCnr0axidv36T/AlxdLqvz/Aqx1Y+c3OHvQ G+e8LjtPgq9T06nuwcXNXTSrfXx6rFxGDcF91EvSbsYC+hR7NgHcLsjK33noL5rdCYlI +C6X8IHpzzUQiGxUJIHmwnlNJMx1uNBiyZbdom90eGbqSDg45EExMac5gunBDdOeZI7+ fLWo2btHrnrZbqiq6yLNe8Kdr6+22Ou+nGIwzy4U9BJ3YSQHds7iJnbhuY7Y4xHz2Tg8 JstQ== X-Gm-Message-State: APjAAAUodM8a3Sm8dgHlc0ryAXkKRxLCKdZqDlRWn6QWl/v6kaBzrjUX 9V5Ol7vfnLmyJQTmutcmwfkSETo= X-Google-Smtp-Source: APXvYqx8BBPkGRkbkxh51Vda0hCmWGbmLbELTdsyOqsj9DzXxQ6aCNFcOQJ0F7RqIwwmeEUyw4LEFw== X-Received: by 2002:a05:620a:2092:: with SMTP id e18mr454323qka.222.1570572513461; Tue, 08 Oct 2019 15:08:33 -0700 (PDT) Received: from localhost.localdomain ([92.117.168.143]) by smtp.gmail.com with ESMTPSA id m19sm42346qke.22.2019.10.08.15.08.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Oct 2019 15:08:32 -0700 (PDT) From: "Viktor Rosendahl (BMW)" To: Steven Rostedt , Ingo Molnar , linux-kernel@vger.kernel.org Cc: Joel Fernandes , "Viktor Rosendahl (BMW)" Subject: [PATCH v8 1/4] ftrace: Implement fs notification for tracing_max_latency Date: Wed, 9 Oct 2019 00:08:21 +0200 Message-Id: <20191008220824.7911-2-viktor.rosendahl@gmail.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20191008220824.7911-1-viktor.rosendahl@gmail.com> References: <20191008220824.7911-1-viktor.rosendahl@gmail.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This patch implements the feature that the tracing_max_latency file, e.g. /sys/kernel/debug/tracing/tracing_max_latency will receive notifications through the fsnotify framework when a new latency is available. One particularly interesting use of this facility is when enabling threshold tracing, through /sys/kernel/debug/tracing/tracing_thresh, together with the preempt/irqsoff tracers. This makes it possible to implement a user space program that can, with equal probability, obtain traces of latencies that occur immediately after each other in spite of the fact that the preempt/irqsoff tracers operate in overwrite mode. This facility works with the hwlat, preempt/irqsoff, and wakeup tracers. The tracers may call the latency_fsnotify() from places such as __schedule() or do_idle(); this makes it impossible to call queue_work() directly without risking a deadlock. The same would happen with a softirq, kernel thread or tasklet. For this reason we use the irq_work mechanism to call queue_work(). This patch creates a new workqueue. The reason for doing this is that I wanted to use the WQ_UNBOUND and WQ_HIGHPRI flags. My thinking was that WQ_UNBOUND might help with the latency in some important cases. If we use: queue_work(system_highpri_wq, &tr->fsnotify_work); then the work will (almost) always execute on the same CPU but if we are unlucky that CPU could be too busy while there could be another CPU in the system that would be able to process the work soon enough. queue_work_on() could be used to queue the work on another CPU but it seems difficult to select the right CPU. Signed-off-by: Viktor Rosendahl (BMW) Reviewed-by: Joel Fernandes (Google) --- kernel/trace/trace.c | 75 +++++++++++++++++++++++++++++++++++++- kernel/trace/trace.h | 18 +++++++++ kernel/trace/trace_hwlat.c | 4 +- 3 files changed, 94 insertions(+), 3 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 252f79c435f8..f8ca307f66cf 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -44,6 +44,9 @@ #include #include #include +#include +#include +#include #include "trace.h" #include "trace_output.h" @@ -1479,6 +1482,74 @@ static ssize_t trace_seq_to_buffer(struct trace_seq *s, void *buf, size_t cnt) } unsigned long __read_mostly tracing_thresh; +static const struct file_operations tracing_max_lat_fops; + +#if (defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)) && \ + defined(CONFIG_FSNOTIFY) + +static struct workqueue_struct *fsnotify_wq; + +static void latency_fsnotify_workfn(struct work_struct *work) +{ + struct trace_array *tr = container_of(work, struct trace_array, + fsnotify_work); + fsnotify(tr->d_max_latency->d_inode, FS_MODIFY, + tr->d_max_latency->d_inode, FSNOTIFY_EVENT_INODE, NULL, 0); +} + +static void latency_fsnotify_workfn_irq(struct irq_work *iwork) +{ + struct trace_array *tr = container_of(iwork, struct trace_array, + fsnotify_irqwork); + queue_work(fsnotify_wq, &tr->fsnotify_work); +} + +static void trace_create_maxlat_file(struct trace_array *tr, + struct dentry *d_tracer) +{ + INIT_WORK(&tr->fsnotify_work, latency_fsnotify_workfn); + init_irq_work(&tr->fsnotify_irqwork, latency_fsnotify_workfn_irq); + tr->d_max_latency = trace_create_file("tracing_max_latency", 0644, + d_tracer, &tr->max_latency, + &tracing_max_lat_fops); +} + +__init static int latency_fsnotify_init(void) +{ + fsnotify_wq = alloc_workqueue("tr_max_lat_wq", + WQ_UNBOUND | WQ_HIGHPRI, 0); + if (!fsnotify_wq) { + pr_err("Unable to allocate tr_max_lat_wq\n"); + return -ENOMEM; + } + return 0; +} + +late_initcall_sync(latency_fsnotify_init); + +void latency_fsnotify(struct trace_array *tr) +{ + if (!fsnotify_wq) + return; + /* + * We cannot call queue_work(&tr->fsnotify_work) from here because it's + * possible that we are called from __schedule() or do_idle(), which + * could cause a deadlock. + */ + irq_work_queue(&tr->fsnotify_irqwork); +} + +/* + * (defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)) && \ + * defined(CONFIG_FSNOTIFY) + */ +#else + +#define trace_create_maxlat_file(tr, d_tracer) \ + trace_create_file("tracing_max_latency", 0644, d_tracer, \ + &tr->max_latency, &tracing_max_lat_fops) + +#endif #ifdef CONFIG_TRACER_MAX_TRACE /* @@ -1518,6 +1589,7 @@ __update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu) /* record this tasks comm */ tracing_record_cmdline(tsk); + latency_fsnotify(tr); } /** @@ -8550,8 +8622,7 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer) create_trace_options_dir(tr); #if defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER) - trace_create_file("tracing_max_latency", 0644, d_tracer, - &tr->max_latency, &tracing_max_lat_fops); + trace_create_maxlat_file(tr, d_tracer); #endif if (ftrace_create_function_files(tr, d_tracer)) diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index f801d154ff6a..591c7a873235 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -16,6 +16,8 @@ #include #include #include +#include +#include #ifdef CONFIG_FTRACE_SYSCALLS #include /* For NR_SYSCALLS */ @@ -264,6 +266,11 @@ struct trace_array { #endif #if defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER) unsigned long max_latency; +#ifdef CONFIG_FSNOTIFY + struct dentry *d_max_latency; + struct work_struct fsnotify_work; + struct irq_work fsnotify_irqwork; +#endif #endif struct trace_pid_list __rcu *filtered_pids; /* @@ -784,6 +791,17 @@ void update_max_tr_single(struct trace_array *tr, struct task_struct *tsk, int cpu); #endif /* CONFIG_TRACER_MAX_TRACE */ +#if (defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)) && \ + defined(CONFIG_FSNOTIFY) + +void latency_fsnotify(struct trace_array *tr); + +#else + +static void latency_fsnotify(struct trace_array *tr) { } + +#endif + #ifdef CONFIG_STACKTRACE void __trace_stack(struct trace_array *tr, unsigned long flags, int skip, int pc); diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c index fa95139445b2..9c379261ee89 100644 --- a/kernel/trace/trace_hwlat.c +++ b/kernel/trace/trace_hwlat.c @@ -254,8 +254,10 @@ static int get_sample(void) trace_hwlat_sample(&s); /* Keep a running maximum ever recorded hardware latency */ - if (sample > tr->max_latency) + if (sample > tr->max_latency) { tr->max_latency = sample; + latency_fsnotify(tr); + } } out: -- 2.17.1