Revert "lib/event: do not spawn a thread for each reactor"

This reverts commit 72eed604b4.

spdk_vhost_init() relies on having a thread on each reactor.
Without the revert, every vhost controller is created on the same
core and even passing --cpumask when creating does not affect it.

Proper fix would be to change spdk_vhost_init(),
but would require additional testing. For now revert the patch
that spawned always idle threads.

Signed-off-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Change-Id: I0dbd6c9fe1d9d23ada260da8fc7b48086223c632
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/6186
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>
Community-CI: Mellanox Build Bot

lib/event/reactor.c

@@ -1010,8 +1010,10 @@ void
 spdk_reactors_start(void)
 {
 	struct spdk_reactor *reactor;
+	struct spdk_cpuset tmp_cpumask = {};
 	uint32_t i, current_core;
 	int rc;
+	char thread_name[32];
 
 	g_rusage_period = (CONTEXT_SWITCH_MONITOR_PERIOD * spdk_get_ticks_hz()) / SPDK_SEC_TO_USEC;
 	g_reactor_state = SPDK_REACTOR_STATE_RUNNING;
@@ -1030,6 +1032,14 @@ spdk_reactors_start(void)
 				assert(false);
 				return;
 			}
+
+			/* For now, for each reactor spawn one thread. */
+			snprintf(thread_name, sizeof(thread_name), "reactor_%u", reactor->lcore);
+
+			spdk_cpuset_zero(&tmp_cpumask);
+			spdk_cpuset_set_cpu(&tmp_cpumask, i, true);
+
+			spdk_thread_create(thread_name, &tmp_cpumask);
 		}
 		spdk_cpuset_set_cpu(&g_reactor_core_mask, i, true);
 	}

test/spdkcli/match_files/spdkcli_details_vhost_ctrl.test.match

@@ -14,7 +14,7 @@
       }
     ]
   },
-  "cpumask": "$(S)",
+  "cpumask": "0x3",
   "ctrlr": "vhost_scsi1",
   "delay_base_us": 20,
   "iops_threshold": 1000000,