Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755513AbcCNKCU (ORCPT ); Mon, 14 Mar 2016 06:02:20 -0400 Received: from szxga03-in.huawei.com ([119.145.14.66]:29957 "EHLO szxga03-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933964AbcCNKBW (ORCPT ); Mon, 14 Mar 2016 06:01:22 -0400 From: Wang Nan To: , CC: , Wang Nan , He Kuang , Alexei Starovoitov , "Arnaldo Carvalho de Melo" , Brendan Gregg , "Jiri Olsa" , Masami Hiramatsu , Namhyung Kim , Zefan Li , Subject: [PATCH 4/5] perf core: Add backward attribute to perf event Date: Mon, 14 Mar 2016 09:59:44 +0000 Message-ID: <1457949585-191064-5-git-send-email-wangnan0@huawei.com> X-Mailer: git-send-email 1.8.3.4 In-Reply-To: <1457949585-191064-1-git-send-email-wangnan0@huawei.com> References: <1457949585-191064-1-git-send-email-wangnan0@huawei.com> MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.107.193.248] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A090205.56E68BA5.0047,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2013-05-26 15:14:31, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: c0d6dd0e4cb188dad62af1b94fd8c861 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3276 Lines: 90 In perf_event_attr a new bit 'write_backward' is appended to indicate this event should write ring buffer from its end to beginning. In perf_output_begin(), prepare ring buffer according this bit. This patch introduces small overhead into perf_output_begin(): an extra memory read and a conditional branch. Further patch can remove this overhead by using custom output handler. Signed-off-by: Wang Nan Cc: He Kuang Cc: Alexei Starovoitov Cc: Arnaldo Carvalho de Melo Cc: Brendan Gregg Cc: Jiri Olsa Cc: Masami Hiramatsu Cc: Namhyung Kim Cc: Peter Zijlstra Cc: Zefan Li Cc: pi3orama@163.com --- include/linux/perf_event.h | 5 +++++ include/uapi/linux/perf_event.h | 3 ++- kernel/events/core.c | 7 +++++++ kernel/events/ring_buffer.c | 2 ++ 4 files changed, 16 insertions(+), 1 deletion(-) diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index d5f99cd..2bf23c9 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -1037,6 +1037,11 @@ static inline bool has_aux(struct perf_event *event) return event->pmu->setup_aux; } +static inline bool is_write_backward(struct perf_event *event) +{ + return !!event->attr.write_backward; +} + extern int perf_output_begin(struct perf_output_handle *handle, struct perf_event *event, unsigned int size); extern void perf_output_end(struct perf_output_handle *handle); diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h index a3c1903..43fc8d2 100644 --- a/include/uapi/linux/perf_event.h +++ b/include/uapi/linux/perf_event.h @@ -340,7 +340,8 @@ struct perf_event_attr { comm_exec : 1, /* flag comm events that are due to an exec */ use_clockid : 1, /* use @clockid for time fields */ context_switch : 1, /* context switch data */ - __reserved_1 : 37; + write_backward : 1, /* Write ring buffer from end to beginning */ + __reserved_1 : 36; union { __u32 wakeup_events; /* wakeup every n events */ diff --git a/kernel/events/core.c b/kernel/events/core.c index ed69532..3da3e38 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -8199,6 +8199,13 @@ perf_event_set_output(struct perf_event *event, struct perf_event *output_event) goto out; /* + * Either writing ring buffer from beginning or from end. + * Mixing is not allowed. + */ + if (is_write_backward(output_event) != is_write_backward(event)) + goto out; + + /* * If both events generate aux data, they must be on the same PMU */ if (has_aux(event) && has_aux(output_event) && diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index 37c11c6..80b1fa7 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -233,6 +233,8 @@ out: int perf_output_begin(struct perf_output_handle *handle, struct perf_event *event, unsigned int size) { + if (unlikely(is_write_backward(event))) + return __perf_output_begin(handle, event, size, true); return __perf_output_begin(handle, event, size, false); } -- 1.8.3.4