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

[Feifei Wang]

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: jer...@marvell.com
Cc: sta...@dpdk.org

Signed-off-by: Feifei Wang <feifei.wa...@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.w...@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