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Commit 94ad6e7e authored by Jiri Olsa's avatar Jiri Olsa Committed by Arnaldo Carvalho de Melo
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perf top: Use cond variable instead of a lock 



Use conditional variable logic to synchronize between the reading and
processing threads. Currently it's done by having mutex around rotation
code.

Using a POSIX cond variable to sync both threads after queues rotation:

  Process thread:

    - Detects data
    - Switches queues
    - Sets rotate variable
    - Waits in pthread_cond_wait()

  Read thread:

    - Detects rotate is set
    - Kicks the process thread with a pthread_cond_signal()

After this rotation is safely completed and both threads can continue
with the new queue.

Signed-off-by: default avatarJiri Olsa <jolsa@kernel.org>
Acked-by: default avatarDavid S. Miller <davem@davemloft.net>
Acked-by: default avatarNamhyung Kim <namhyung@kernel.org>
Tested-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-3rdeg23rv3brvy1pwt3igvyw@git.kernel.org


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 16c66bc1

tools/perf/builtin-top.c

+17 −7
Original line number Diff line number Diff line
@@ -846,13 +846,18 @@ static void perf_top__mmap_read_idx(struct perf_top *top, int idx) 
		if (ret && ret != -1)

			break;



		pthread_mutex_lock(&top->qe.lock);

		ret = ordered_events__queue(top->qe.in, event, timestamp, 0);

		pthread_mutex_unlock(&top->qe.lock);



		perf_mmap__consume(md);

		if (ret)

			break;



		perf_mmap__consume(md);



		if (top->qe.rotate) {

			pthread_mutex_lock(&top->qe.mutex);

			top->qe.rotate = false;

			pthread_cond_signal(&top->qe.cond);

			pthread_mutex_unlock(&top->qe.mutex);

		}

	}



	perf_mmap__read_done(md);
@@ -1059,9 +1064,12 @@ static void *process_thread(void *arg) 
			continue;

		}



		pthread_mutex_lock(&top->qe.lock);

		out = rotate_queues(top);

		pthread_mutex_unlock(&top->qe.lock);



		pthread_mutex_lock(&top->qe.mutex);

		top->qe.rotate = true;

		pthread_cond_wait(&top->qe.cond, &top->qe.mutex);

		pthread_mutex_unlock(&top->qe.mutex);



		if (ordered_events__flush(out, OE_FLUSH__TOP))

			pr_err("failed to process events\n");
@@ -1151,7 +1159,8 @@ static void init_process_thread(struct perf_top *top) 
	ordered_events__set_copy_on_queue(&top->qe.data[0], true);

	ordered_events__set_copy_on_queue(&top->qe.data[1], true);

	top->qe.in = &top->qe.data[0];

	pthread_mutex_init(&top->qe.lock, NULL);

	pthread_mutex_init(&top->qe.mutex, NULL);

	pthread_cond_init(&top->qe.cond, NULL);

}



static int __cmd_top(struct perf_top *top)
@@ -1271,6 +1280,7 @@ static int __cmd_top(struct perf_top *top) 
out_join:

	pthread_join(thread, NULL);

out_join_thread:

	pthread_cond_signal(&top->qe.cond);

	pthread_join(thread_process, NULL);

out_delete:

	perf_session__delete(top->session);

tools/perf/util/top.h

+3 −1
Original line number Diff line number Diff line
@@ -44,7 +44,9 @@ struct perf_top { 
	struct {

		struct ordered_events	*in;

		struct ordered_events	 data[2];

		pthread_mutex_t		 lock;

		bool			 rotate;

		pthread_mutex_t		 mutex;

		pthread_cond_t		 cond;

	} qe;

};