From patchwork Tue Apr 20 22:47:11 2010 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Miller X-Patchwork-Id: 50602 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 7FCB3B7D11 for ; Wed, 21 Apr 2010 08:47:11 +1000 (EST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753186Ab0DTWrJ (ORCPT ); Tue, 20 Apr 2010 18:47:09 -0400 Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:48177 "EHLO sunset.davemloft.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751702Ab0DTWrJ (ORCPT ); Tue, 20 Apr 2010 18:47:09 -0400 Received: from localhost (localhost [127.0.0.1]) by sunset.davemloft.net (Postfix) with ESMTP id B348724C090; Tue, 20 Apr 2010 15:47:11 -0700 (PDT) Date: Tue, 20 Apr 2010 15:47:11 -0700 (PDT) Message-Id: <20100420.154711.11246950.davem@davemloft.net> To: rostedt@goodmis.org CC: fweisbec@gmail.com, linux-kernel@vger.kernel.org, sparclinux@vger.kernel.org Subject: [PATCH] ring-buffer: Make non-consuming read less expensive with lots of cpus. From: David Miller X-Mailer: Mew version 6.3 on Emacs 23.1 / Mule 6.0 (HANACHIRUSATO) Mime-Version: 1.0 Sender: sparclinux-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: sparclinux@vger.kernel.org When performing a non-consuming read, a synchronize_sched() is performed once for every cpu which is actively tracing. This is very expensive, and can make it take several seconds to open up the 'trace' file with lots of cpus. Only one synchronize_sched() call is actually necessary. What is desired is for all cpus to see the disabling state change. So we transform the existing sequence: for_each_cpu() { ring_buffer_read_start(); } where each ring_buffer_start() call performs a synchronize_sched(), into the following: for_each_cpu() { ring_buffer_read_prepare(); } ring_buffer_read_prepare_sync(); for_each_cpu() { ring_buffer_read_start(); } wherein only the single ring_buffer_read_prepare_sync() call needs to do the synchronize_sched(). The first phase, via ring_buffer_read_prepare(), allocates the 'iter' memory and increments ->record_disabled. In the second phase, ring_buffer_read_prepare_sync() makes sure this ->record_disabled state is visible fully to all cpus. And in the final third phase, the ring_buffer_read_start() calls reset the 'iter' objects allocated in the first phase since we now know that none of the cpus are adding trace entries any more. This makes openning the 'trace' file nearly instantaneous on a sparc64 Niagara2 box with 128 cpus tracing. Signed-off-by: David S. Miller --- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index 5fcc31e..827848e 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -125,7 +125,9 @@ struct ring_buffer_event * ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts); struct ring_buffer_iter * -ring_buffer_read_start(struct ring_buffer *buffer, int cpu); +ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu); +void ring_buffer_read_prepare_sync(void); +void ring_buffer_read_start(struct ring_buffer_iter *iter); void ring_buffer_read_finish(struct ring_buffer_iter *iter); struct ring_buffer_event * diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 41ca394..ca4be22 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -3276,23 +3276,30 @@ ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts) EXPORT_SYMBOL_GPL(ring_buffer_consume); /** - * ring_buffer_read_start - start a non consuming read of the buffer + * ring_buffer_read_prepare - Prepare for a non consuming read of the buffer * @buffer: The ring buffer to read from * @cpu: The cpu buffer to iterate over * - * This starts up an iteration through the buffer. It also disables - * the recording to the buffer until the reading is finished. - * This prevents the reading from being corrupted. This is not - * a consuming read, so a producer is not expected. + * This performs the initial preparations necessary to iterate + * through the buffer. Memory is allocated, buffer recording + * is disabled, and the iterator pointer is returned to the caller. * - * Must be paired with ring_buffer_finish. + * Disabling buffer recordng prevents the reading from being + * corrupted. This is not a consuming read, so a producer is not + * expected. + * + * After a sequence of ring_buffer_read_prepare calls, the user is + * expected to make at least one call to ring_buffer_prepare_sync. + * Afterwards, ring_buffer_read_start is invoked to get things going + * for real. + * + * This overall must be paired with ring_buffer_finish. */ struct ring_buffer_iter * -ring_buffer_read_start(struct ring_buffer *buffer, int cpu) +ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu) { struct ring_buffer_per_cpu *cpu_buffer; struct ring_buffer_iter *iter; - unsigned long flags; if (!cpumask_test_cpu(cpu, buffer->cpumask)) return NULL; @@ -3306,15 +3313,52 @@ ring_buffer_read_start(struct ring_buffer *buffer, int cpu) iter->cpu_buffer = cpu_buffer; atomic_inc(&cpu_buffer->record_disabled); + + return iter; +} +EXPORT_SYMBOL_GPL(ring_buffer_read_prepare); + +/** + * ring_buffer_read_prepare_sync - Synchronize a set of prepare calls + * + * All previously invoked ring_buffer_read_prepare calls to prepare + * iterators will be synchronized. Afterwards, read_buffer_read_start + * calls on those iterators are allowed. + */ +void +ring_buffer_read_prepare_sync(void) +{ synchronize_sched(); +} +EXPORT_SYMBOL_GPL(ring_buffer_read_prepare_sync); + +/** + * ring_buffer_read_start - start a non consuming read of the buffer + * @iter: The iterator returned by ring_buffer_read_prepare + * + * This finalizes the startup of an iteration through the buffer. + * The iterator comes from a call to ring_buffer_read_prepare and + * an intervening ring_buffer_read_prepare_sync must have been + * performed. + * + * Must be paired with ring_buffer_finish. + */ +void +ring_buffer_read_start(struct ring_buffer_iter *iter) +{ + struct ring_buffer_per_cpu *cpu_buffer; + unsigned long flags; + + if (!iter) + return; + + cpu_buffer = iter->cpu_buffer; spin_lock_irqsave(&cpu_buffer->reader_lock, flags); arch_spin_lock(&cpu_buffer->lock); rb_iter_reset(iter); arch_spin_unlock(&cpu_buffer->lock); spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); - - return iter; } EXPORT_SYMBOL_GPL(ring_buffer_read_start); diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 44f916a..3f161d8 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -2166,15 +2166,20 @@ __tracing_open(struct inode *inode, struct file *file) if (iter->cpu_file == TRACE_PIPE_ALL_CPU) { for_each_tracing_cpu(cpu) { - iter->buffer_iter[cpu] = - ring_buffer_read_start(iter->tr->buffer, cpu); + ring_buffer_read_prepare(iter->tr->buffer, cpu); + } + ring_buffer_read_prepare_sync(); + for_each_tracing_cpu(cpu) { + ring_buffer_read_start(iter->buffer_iter[cpu]); tracing_iter_reset(iter, cpu); } } else { cpu = iter->cpu_file; iter->buffer_iter[cpu] = - ring_buffer_read_start(iter->tr->buffer, cpu); + ring_buffer_read_prepare(iter->tr->buffer, cpu); + ring_buffer_read_prepare_sync(); + ring_buffer_read_start(iter->buffer_iter[cpu]); tracing_iter_reset(iter, cpu); }