[dpdk-dev] [RFC PATCH v1 1/6] app/eventdev: fix SMP barrier bugs for perf test

[Feifei Wang <feifei.wang2@arm.com>]

This patch fixes RTE SMP barrier bugs for the perf test of eventdev.

For the "perf_process_last_stage" function, wmb after storing
processed_pkts should be moved before it. This is because the worker
lcore should ensure it has really finished data processing, e.g. event
stored into buffers, before the shared variables "w->processed_pkts"are
stored.

For the "perf_process_last_stage_latency", on the one hand, the wmb
should be moved before storing into "w->processed_pkts". The reason is
the same as above. But on the other hand, for "w->latency", wmb is
unnecessary due to data dependency.

Fixes: 2369f73329f8 ("app/testeventdev: add perf queue worker functions")
Cc: jerinj@marvell.com
Cc: stable@dpdk.org

Signed-off-by: Feifei Wang <feifei.wang2@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
---
 app/test-eventdev/test_perf_common.h | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/app/test-eventdev/test_perf_common.h b/app/test-eventdev/test_perf_common.h
index ff9705df8..e7233e5a5 100644
--- a/app/test-eventdev/test_perf_common.h
+++ b/app/test-eventdev/test_perf_common.h
@@ -97,8 +97,13 @@ perf_process_last_stage(struct rte_mempool *const pool,
 		void *bufs[], int const buf_sz, uint8_t count)
 {
 	bufs[count++] = ev->event_ptr;
-	w->processed_pkts++;
+
+	/* wmb here ensures event_prt is stored before
+	 * updating the number of processed packets
+	 * for worker lcores
+	 */
 	rte_smp_wmb();
+	w->processed_pkts++;
 
 	if (unlikely(count == buf_sz)) {
 		count = 0;
@@ -116,6 +121,12 @@ perf_process_last_stage_latency(struct rte_mempool *const pool,
 	struct perf_elt *const m = ev->event_ptr;
 
 	bufs[count++] = ev->event_ptr;
+
+	/* wmb here ensures event_prt is stored before
+	 * updating the number of processed packets
+	 * for worker lcores
+	 */
+	rte_smp_wmb();
 	w->processed_pkts++;
 
 	if (unlikely(count == buf_sz)) {
@@ -127,7 +138,6 @@ perf_process_last_stage_latency(struct rte_mempool *const pool,
 	}
 
 	w->latency += latency;
-	rte_smp_wmb();
 	return count;
 }
 
-- 
2.17.1