accel_perf: check accel engine usage in accel_perf_start function.

In accel_done function, we use g_using_sw_engine to
determine to directly call _accel_done or use thread message
passing way.

However when we get the capability and determine the
value of g_using_sw_engine in mulitple cases. We do not
protect the value of g_num_workers. Then if we use CPU mode
to do test, g_using_sw_engine will not set to be false
in racing condition. Since the value of g_num_workers can be
> 1 when we do the check, i.e., it is a TOC2TOU issue.

The solution is that we check the g_using_sw_engine in
accel_perf_start function.

Fixes issue spdk#2084

Change-Id: I55c18e0443120adb698d5bd27d4522df09f6dcab
Signed-off-by: Ziye Yang <[email protected]>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/9151
Community-CI: Broadcom CI <[email protected]>
Community-CI: Mellanox Build Bot
Tested-by: SPDK CI Jenkins <[email protected]>
Reviewed-by: Jim Harris <[email protected]>
Reviewed-by: Ben Walker <[email protected]>

examples/accel/perf/accel_perf.c

@@ -820,7 +820,6 @@ _init_thread(void *arg1)
 	struct accel_batch *tmp;
 	struct accel_batch *worker_batch = NULL;
 	struct display_info *display = arg1;
-	uint64_t capabilities;
 
 	worker = calloc(1, sizeof(*worker));
 	if (worker == NULL) {
@@ -841,15 +840,6 @@ _init_thread(void *arg1)
 	pthread_mutex_unlock(&g_workers_lock);
 	worker->ch = spdk_accel_engine_get_io_channel();
 
-	if (g_num_workers == 1) {
-		capabilities = spdk_accel_get_capabilities(worker->ch);
-		if ((capabilities & g_workload_selection) != g_workload_selection) {
-			g_using_sw_engine = true;
-			SPDK_WARNLOG("The selected workload is not natively supported by the current engine\n");
-			SPDK_WARNLOG("The software engine will be used instead.\n\n");
-		}
-	}
-
 	TAILQ_INIT(&worker->tasks_pool);
 
 	if (g_ops_per_batch > 0) {
@@ -1004,6 +994,25 @@ accel_done(void *cb_arg, int status)
 	}
 }
 
+static inline void
+identify_accel_engine_usage(void)
+{
+	struct spdk_io_channel *ch;
+	uint64_t capabilities;
+
+	ch = spdk_accel_engine_get_io_channel();
+	assert(ch != NULL);
+
+	capabilities = spdk_accel_get_capabilities(ch);
+	if ((capabilities & g_workload_selection) != g_workload_selection) {
+		g_using_sw_engine = true;
+		SPDK_WARNLOG("The selected workload is not natively supported by the current engine\n");
+		SPDK_WARNLOG("The software engine will be used instead.\n\n");
+	}
+
+	spdk_put_io_channel(ch);
+}
+
 static void
 accel_perf_start(void *arg1)
 {
@@ -1014,6 +1023,8 @@ accel_perf_start(void *arg1)
 	struct spdk_thread *thread;
 	struct display_info *display;
 
+	identify_accel_engine_usage();
+
 	g_tsc_rate = spdk_get_ticks_hz();
 	g_tsc_end = spdk_get_ticks() + g_time_in_sec * g_tsc_rate;