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perf/ring_buffer: Introduce new ioctl options to pause and resume the ring-buffer

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Add new ioctl() to pause/resume ring-buffer output.

In some situations we want to read from the 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 a prerequisite to enable overwrite support for the
perf ring-buffer support. 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 <wangnan0@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <pi3orama@163.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: Zefan Li <lizefan@huawei.com>
Link: http://lkml.kernel.org/r/1459147292-239310-2-git-send-email-wangnan0@huawei.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Wang Nan 2016-03-28 06:41:29 +00:00 committed by Ingo Molnar
parent 0a74c5b3d2
commit 86e7972f69
4 changed files with 34 additions and 1 deletions
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1
include/uapi/linux/perf_event.h
View file

@ -401,6 +401,7 @@ struct perf_event_attr {
#define PERF_EVENT_IOC_SET_FILTER _IOW('$', 6, char *)
#define PERF_EVENT_IOC_ID _IOR('$', 7, __u64 *)
#define PERF_EVENT_IOC_SET_BPF _IOW('$', 8, __u32)
#define PERF_EVENT_IOC_PAUSE_OUTPUT _IOW('$', 9, __u32)
enum perf_event_ioc_flags {
PERF_IOC_FLAG_GROUP = 1U << 0,

13
kernel/events/core.c
View file

@ -4379,6 +4379,19 @@ static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned lon
case PERF_EVENT_IOC_SET_BPF:
return perf_event_set_bpf_prog(event, arg);
case PERF_EVENT_IOC_PAUSE_OUTPUT: {
struct ring_buffer *rb;
rcu_read_lock();
rb = rcu_dereference(event->rb);
if (!rb || !rb->nr_pages) {
rcu_read_unlock();
return -EINVAL;
}
rb_toggle_paused(rb, !!arg);
rcu_read_unlock();
return 0;
}
default:
return -ENOTTY;
}

9
kernel/events/internal.h
View file

@ -17,6 +17,7 @@ struct ring_buffer {
#endif
int nr_pages; /* nr of data pages */
int overwrite; /* can overwrite itself */
int paused; /* can write into ring buffer */
atomic_t poll; /* POLL_ for wakeups */
@ -64,6 +65,14 @@ static inline void rb_free_rcu(struct rcu_head *rcu_head)
rb_free(rb);
}
static inline void rb_toggle_paused(struct ring_buffer *rb, bool pause)
{
if (!pause && rb->nr_pages)
rb->paused = 0;
else
rb->paused = 1;
}
extern struct ring_buffer *
rb_alloc(int nr_pages, long watermark, int cpu, int flags);
extern void perf_event_wakeup(struct perf_event *event);

12
kernel/events/ring_buffer.c
View file

@ -125,8 +125,11 @@ int perf_output_begin(struct perf_output_handle *handle,
if (unlikely(!rb))
goto out;
if (unlikely(!rb->nr_pages))
if (unlikely(rb->paused)) {
if (rb->nr_pages)
local_inc(&rb->lost);
goto out;
}
handle->rb = rb;
handle->event = event;
@ -241,6 +244,13 @@ ring_buffer_init(struct ring_buffer *rb, long watermark, int flags)
INIT_LIST_HEAD(&rb->event_list);
spin_lock_init(&rb->event_lock);
/*
* 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;
}
/*