Add perf context support for ARMv7

Instead of closing the perf context after the page has been mapped, keep it open so it can be used with the read() system call if the architecture does not support direct access from user-space.

Signed-off-by Julien Desfossez <[email protected]>

---
liblttng-ust/lttng-context-perf-counters.c | 65 +++++++++++++++++++++++-------

1 file changed, 50 insertions(+), 15 deletions(-)

liblttng-ust/lttng-context-perf-counters.c +1 -0

index 97ddf97..db756d6 100644
@@ -55,6 +55,7 @@ struct lttng_perf_counter_thread_field {
 	struct perf_event_mmap_page *pc;
 	struct cds_list_head thread_field_node;	/* Per-field list of thread fields
 	(node) */
 	struct cds_list_head rcu_field_node;	/* RCU per-thread list of fields (node) */
+	int fd;					/* Perf FD */
 };
 

struct lttng_perf_counter_thread {

liblttng-ust/lttng-context-perf-counters.c +5 -0

@@ -90,6 +91,11 @@ uint64_t rdpmc(unsigned int counter)
 	return low | ((uint64_t) high) << 32;
 }
 
+static bool arch_perf_use_read(void)
+{
+	return false;
+}
+
 #else /* defined(__x86_64__) || defined(__i386__) */
 
 #error "Perf event counters are only supported on x86 so far."

@@ -131,27 +137,51 @@ int sys_perf_event_open(struct perf_event_attr *attr,
 }
 

static

liblttng-ust/lttng-context-perf-counters.c +1 -1

-struct perf_event_mmap_page *setup_perf(struct perf_event_attr *attr)
+int open_perf_fd(struct perf_event_attr *attr)

{

liblttng-ust/lttng-context-perf-counters.c +1 -2

-	void *perf_addr;
-	int fd, ret;
+	int fd;

	fd = sys_perf_event_open(attr, 0, -1, -1, 0);
	if (fd < 0)

liblttng-ust/lttng-context-perf-counters.c +10 -1

-		return NULL;
+		return -1;
+
+	return fd;
+}
+
+static
+struct perf_event_mmap_page *setup_perf(
+		struct lttng_perf_counter_thread_field *thread_field)
+{
+	void *perf_addr;

perf_addr = mmap(NULL, sizeof(struct perf_event_mmap_page),

liblttng-ust/lttng-context-perf-counters.c +1 -1

-			PROT_READ, MAP_SHARED, fd, 0);
+			PROT_READ, MAP_SHARED, thread_field->fd, 0);

	if (perf_addr == MAP_FAILED)

liblttng-ust/lttng-context-perf-counters.c +5 -4

-		return NULL;
-	ret = close(fd);
-	if (ret) {
-		perror("Error closing LTTng-UST perf memory mapping FD");
+		perf_addr = NULL;
+
+	if (!arch_perf_use_read()) {
+		close_perf_fd(thread_field->fd);
+		thread_field->fd = -1;

	}

liblttng-ust/lttng-context-perf-counters.c +2 -0

+
+end:

	return perf_addr;
}

static

liblttng-ust/lttng-context-perf-counters.c +13 -0

+void close_perf_fd(int fd)
+{
+	int ret;
+
+	if (fd < 0)
+		return;
+
+	ret = close(fd);
+	if (ret)
+		perror("Error closing LTTng-UST perf memory mapping FD");
+}
+
+static

void unmap_perf_page(struct perf_event_mmap_page *pc)

{
	int ret;

liblttng-ust/lttng-context-perf-counters.c +7 -2

@@ -221,8 +251,13 @@ struct lttng_perf_counter_thread_field *
 	if (!thread_field)
 		abort();
 	thread_field->field = perf_field;
-	thread_field->pc = setup_perf(&perf_field->attr);
-	/* Note: thread_field->pc can be NULL if setup_perf() fails. */
+	thread_field->fd = open_perf_fd(&perf_field->attr);
+	if (thread_field->fd >= 0)
+		thread_field->pc = setup_perf(thread_field);
+	/*
+	 * Note: thread_field->pc can be NULL if setup_perf() fails.
+	 * Also, thread_field->fd can be -1 if open_perf_fd fails.
+	 */
 	ust_lock_nocheck();
 	cds_list_add_rcu(&thread_field->rcu_field_node,
 			&perf_thread->rcu_field_list);

@@ -293,6 +328,7 @@ static

void lttng_destroy_perf_thread_field(
struct lttng_perf_counter_thread_field *thread_field)
{

liblttng-ust/lttng-context-perf-counters.c +1 -0

+	close_perf_fd(thread_field->fd);

	unmap_perf_page(thread_field->pc);
	cds_list_del_rcu(&thread_field->rcu_field_node);
	cds_list_del(&thread_field->thread_field_node);

liblttng-ust/lttng-context-perf-counters.c +3 -5

@@ -341,7 +377,6 @@ int lttng_add_perf_counter_to_ctx(uint32_t type,
 {
 	struct lttng_ctx_field *field;
 	struct lttng_perf_counter_field *perf_field;
-	struct perf_event_mmap_page *tmp_pc;
 	char *name_alloc;
 	int ret;
 

@@ -389,12 +424,12 @@ int lttng_add_perf_counter_to_ctx(uint32_t type,
 	field->u.perf_counter = perf_field;
 
 	/* Ensure that this perf counter can be used in this process. */
-	tmp_pc = setup_perf(&perf_field->attr);
-	if (!tmp_pc) {
+	ret = open_perf_fd(&perf_field->attr);
+	if (ret < 0) {
 		ret = -ENODEV;
 		goto setup_error;
 	}
-	unmap_perf_page(tmp_pc);
+	close_perf_fd(ret);
 
 	/*
 	 * Contexts can only be added before tracing is started, so we
--

1.9.1

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