Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756068AbcC2Myh (ORCPT ); Tue, 29 Mar 2016 08:54:37 -0400 Received: from casper.infradead.org ([85.118.1.10]:47280 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752375AbcC2Mye (ORCPT ); Tue, 29 Mar 2016 08:54:34 -0400 Date: Tue, 29 Mar 2016 14:54:23 +0200 From: Peter Zijlstra To: Wang Nan Cc: Alexei Starovoitov , Arnaldo Carvalho de Melo , linux-kernel@vger.kernel.org, Brendan Gregg , He Kuang , Jiri Olsa , Masami Hiramatsu , Namhyung Kim , pi3orama@163.com, Zefan Li Subject: Re: [PATCH 1/4] perf core: Introduce new ioctl options to pause and resume ring buffer Message-ID: <20160329125423.GJ3408@twins.programming.kicks-ass.net> References: <1459147292-239310-1-git-send-email-wangnan0@huawei.com> <1459147292-239310-2-git-send-email-wangnan0@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1459147292-239310-2-git-send-email-wangnan0@huawei.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1780 Lines: 57 On Mon, Mar 28, 2016 at 06:41:29AM +0000, Wang Nan wrote: > Add new ioctl() to pause/resume ring-buffer output. > > In some situations we want to read from ring buffer only when we > ensure nothing can write to the ring buffer during reading. Without > this patch we have to turn off all events attached to this ring buffer > to achieve this. > > This patch is for supporting overwrite ring buffer. Following > commits will introduce new methods support reading from overwrite ring > buffer. Before reading, caller must ensure the ring buffer is frozen, or > the reading is unreliable. > > Signed-off-by: Wang Nan I made the below changes. --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -4346,7 +4346,7 @@ static long _perf_ioctl(struct perf_even rcu_read_lock(); rb = rcu_dereference(event->rb); - if (!event->rb) { + if (!event->rb || !event->nr_pages) { rcu_read_unlock(); return -EINVAL; } --- a/kernel/events/internal.h +++ b/kernel/events/internal.h @@ -66,9 +66,7 @@ static inline void rb_free_rcu(struct rc rb_free(rb); } -static inline void -rb_toggle_paused(struct ring_buffer *rb, - bool pause) +static inline void rb_toggle_paused(struct ring_buffer *rb, bool pause) { if (!pause && rb->nr_pages) rb->paused = 0; --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -248,7 +248,12 @@ ring_buffer_init(struct ring_buffer *rb, spin_lock_init(&rb->event_lock); init_irq_work(&rb->irq_work, rb_irq_work); - rb->paused = rb->nr_pages ? 0 : 1; + /* + * perf_output_begin() only checks rb->paused, therefore + * rb->paused must be true if we have no pages for output. + */ + if (!rb->nr_pages) + rb->paused = 1; } static void ring_buffer_put_async(struct ring_buffer *rb)