sheep: cache eventfd for local request in thread local storage

Creating a fd must be serialized because of the minimum available fd
allocation rule of Posix, so current implementation of the local
request is bad for multicore scalability.

Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>

sheep/request.c

@@ -544,10 +544,16 @@ worker_fn int exec_local_req(struct sd_req *rq, void *data)
 {
 	struct request *req;
 	int ret;
+	static __thread int efd = -1;
 
 	req = alloc_local_request(data, rq->data_length);
 	req->rq = *rq;
-	req->local_req_efd = eventfd(0, 0);
+
+	if (unlikely(efd == -1))
+		efd = eventfd(0, 0);
+
+	req->local_req_efd = efd;
+
 	if (req->local_req_efd < 0) {
 		sd_err("eventfd failed, %m");
 		/* Fake the result to ask for retry */
@@ -561,7 +567,6 @@ worker_fn int exec_local_req(struct sd_req *rq, void *data)
 	/* fill rq with response header as exec_req does */
 	memcpy(rq, &req->rp, sizeof(req->rp));
 
-	close(req->local_req_efd);
 	ret = req->rp.result;
 	free_local_request(req);