[DTrace-devel] [PATCH] Review perf_event_open() calls

[eugene.loh at oracle.com]

From: Eugene Loh <eugene.loh at oracle.com>

Our perf_event_open() calls should be cleaned up a little.  The issues
are minor, with no user-observable effects, but cleaner code is better.

Set size in "struct perf_event_attr".

Use flag PERF_FLAG_FD_CLOEXEC.

Use PERF_SAMPLE_RAW only for the perf_event buffer to which BPF programs
will write.

Distribute perf_events evenly among CPUs.  (Note that perf_event buffers
and profile-n events are one-per-CPU.  Further, tick-n events are
distributed randomly for load balancing.  The only change needed is to
distribute tp_attach() randomly over CPUs rather than mapping them all
to CPU 0.)

Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
---
 libdtrace/dt_peb.c          | 1 +
 libdtrace/dt_prov_profile.c | 3 +--
 libdtrace/dt_prov_sdt.c     | 8 ++++++--
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/libdtrace/dt_peb.c b/libdtrace/dt_peb.c
index 0ef1c419..b8c49e2f 100644
--- a/libdtrace/dt_peb.c
+++ b/libdtrace/dt_peb.c
@@ -75,6 +75,7 @@ dt_peb_open(dt_peb_t *peb)
 	memset(&attr, 0, sizeof(attr));
 	attr.config = PERF_COUNT_SW_BPF_OUTPUT;
 	attr.type = PERF_TYPE_SOFTWARE;
+	attr.size = sizeof(struct perf_event_attr);
 	attr.sample_type = PERF_SAMPLE_RAW;
 	attr.sample_period = 1;
 	attr.wakeup_events = 1;
diff --git a/libdtrace/dt_prov_profile.c b/libdtrace/dt_prov_profile.c
index 8541bee6..22cd968a 100644
--- a/libdtrace/dt_prov_profile.c
+++ b/libdtrace/dt_prov_profile.c
@@ -293,7 +293,6 @@ static int attach(dtrace_hdl_t *dtp, const dt_probe_t *prp, int bpf_fd)
 	memset(&attr, 0, sizeof(attr));
 	attr.type = PERF_TYPE_SOFTWARE;
 	attr.config = PERF_COUNT_SW_CPU_CLOCK;
-	attr.sample_type = PERF_SAMPLE_RAW;
 	attr.size = sizeof(struct perf_event_attr);
 	attr.wakeup_events = 1;
 	attr.freq = 0;
@@ -307,7 +306,7 @@ static int attach(dtrace_hdl_t *dtp, const dt_probe_t *prp, int bpf_fd)
 			j = rand() % dtp->dt_conf.num_online_cpus;
 
 		fd = perf_event_open(&attr, -1, dtp->dt_conf.cpus[j].cpu_id,
-				     -1, 0);
+				     -1, PERF_FLAG_FD_CLOEXEC);
 		if (fd < 0)
 			continue;
 		if (ioctl(fd, PERF_EVENT_IOC_SET_BPF, bpf_fd) < 0) {
diff --git a/libdtrace/dt_prov_sdt.c b/libdtrace/dt_prov_sdt.c
index 4b2ac31b..8775103f 100644
--- a/libdtrace/dt_prov_sdt.c
+++ b/libdtrace/dt_prov_sdt.c
@@ -77,14 +77,18 @@ int tp_attach(dtrace_hdl_t *dtp, const dt_probe_t *prp, int bpf_fd)
 	if (datap->event_fd == -1) {
 		int			fd;
 		struct perf_event_attr	attr = { 0, };
+		int			cpu_index, cpu;
+
+		cpu_index = rand() % dtp->dt_conf.num_online_cpus;
+		cpu = dtp->dt_conf.cpus[cpu_index].cpu_id;
 
 		attr.type = PERF_TYPE_TRACEPOINT;
-		attr.sample_type = PERF_SAMPLE_RAW;
+		attr.size = sizeof(struct perf_event_attr);
 		attr.sample_period = 1;
 		attr.wakeup_events = 1;
 		attr.config = datap->event_id;
 
-		fd = perf_event_open(&attr, -1, 0, -1, 0);
+		fd = perf_event_open(&attr, -1, cpu, -1, PERF_FLAG_FD_CLOEXEC);
 		if (fd < 0)
 			return dt_set_errno(dtp, errno);
 
-- 
2.18.4