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Miller" , He Kuang , Jiri Olsa , Li Zefan , Masami Hiramatsu , Namhyung Kim , Peter Zijlstra , , Will Deacon , , Wang Nan Subject: [PATCH 21/54] perf core: Add backward attribute to perf event Date: Mon, 25 Jan 2016 09:56:08 +0000 Message-ID: <1453715801-7732-22-git-send-email-wangnan0@huawei.com> X-Mailer: git-send-email 1.8.3.4 In-Reply-To: <1453715801-7732-1-git-send-email-wangnan0@huawei.com> References: <1453715801-7732-1-git-send-email-wangnan0@huawei.com> MIME-Version: 1.0 X-Originating-IP: [10.107.193.248] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A020201.56A5F187.0090, ss=1, re=0.000, recu=0.000, reip=0.000, cl=1, cld=1, fgs=0, ip=0.0.0.0, so=2013-06-18 04:22:30, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: 57d0288e036e7a13be72c6741ed81c01 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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(-) -- 1.8.3.4 diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index f9828a4..54c3fb2 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -1032,6 +1032,11 @@ 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 f79c4be..8ad22a5 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -8107,6 +8107,13 @@ 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 0684e880..28543e1 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); }