From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756936AbcCDNnf (ORCPT ); Fri, 4 Mar 2016 08:43:35 -0500 Received: from mga09.intel.com ([134.134.136.24]:48213 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755873AbcCDNn3 (ORCPT ); Fri, 4 Mar 2016 08:43:29 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.22,535,1449561600"; d="scan'208";a="59824660" From: Alexander Shishkin To: Peter Zijlstra Cc: Ingo Molnar , linux-kernel@vger.kernel.org, vince@deater.net, eranian@google.com, Arnaldo Carvalho de Melo , Alexander Shishkin , Mathieu Poirier Subject: [PATCH v2 3/5] perf: Document aux api usage Date: Fri, 4 Mar 2016 15:42:47 +0200 Message-Id: <1457098969-21595-4-git-send-email-alexander.shishkin@linux.intel.com> X-Mailer: git-send-email 2.7.0 In-Reply-To: <1457098969-21595-1-git-send-email-alexander.shishkin@linux.intel.com> References: <1457098969-21595-1-git-send-email-alexander.shishkin@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In order to ensure safe aux buffer management, we rely on the assumption that pmu::stop() stops its ongoing aux transaction and not just the hw. This patch documents this requirement for perf_aux_output_{begin,end}() apis. Signed-off-by: Alexander Shishkin Cc: Mathieu Poirier --- kernel/events/ring_buffer.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index fb7f5bce27..b5feb7ebb9 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -252,6 +252,10 @@ ring_buffer_init(struct ring_buffer *rb, long watermark, int flags) * The ordering is similar to that of perf_output_{begin,end}, with * the exception of (B), which should be taken care of by the pmu * driver, since ordering rules will differ depending on hardware. + * + * Call this from pmu::start(); see the comment in perf_aux_output_end() + * about its use in pmu callbacks. Both can also be called from the PMI + * handler if needed. */ void *perf_aux_output_begin(struct perf_output_handle *handle, struct perf_event *event) @@ -323,6 +327,7 @@ void *perf_aux_output_begin(struct perf_output_handle *handle, return handle->rb->aux_priv; err_put: + /* can't be last */ rb_free_aux(rb); err: @@ -337,6 +342,10 @@ err: * aux_head and posting a PERF_RECORD_AUX into the perf buffer. It is the * pmu driver's responsibility to observe ordering rules of the hardware, * so that all the data is externally visible before this is called. + * + * Note: this has to be called from pmu::stop() callback, as the assumption + * of the aux buffer management code is that after pmu::stop(), the aux + * transaction must be stopped and therefore drop the aux reference count. */ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size, bool truncated) @@ -376,6 +385,7 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size, handle->event = NULL; local_set(&rb->aux_nest, 0); + /* can't be last */ rb_free_aux(rb); ring_buffer_put(rb); } -- 2.7.0