smb: client: spread cifsd threads through available CPUs

Spawn cifsd thread on each available CPU.
Iterate in a round-robin fashion, but prefer the next one without a
cifsd instance running.

~10% performance improvement is observed on heavy workloads with
multichannel enabled.

Signed-off-by: Enzo Matsumiya <ematsumiya@suse.de>

2 files changed, 66 insertions, 15 deletions

diff --git a/fs/smb/client/cifsglob.h b/fs/smb/client/cifsglob.h
index 3b32116b0b49..d50466930c13 100644
--- a/fs/smb/client/cifsglob.h
+++ b/fs/smb/client/cifsglob.h
@@ -744,6 +744,7 @@ struct TCP_Server_Info {
 	struct mutex _srv_mutex;
 	unsigned int nofs_flag;
 	struct task_struct *tsk;
+	unsigned int tsk_cpu;
 	char server_GUID[16];
 	__u16 sec_mode;
 	bool sign; /* is signing enabled on this connection? */
diff --git a/fs/smb/client/connect.c b/fs/smb/client/connect.c
index 6bf04d9a5491..af728cfccf54 100644
--- a/fs/smb/client/connect.c
+++ b/fs/smb/client/connect.c
@@ -65,6 +65,17 @@ static void tlink_rb_insert(struct rb_root *root, struct tcon_link *new_tlink);
 static void cifs_prune_tlinks(struct work_struct *work);
 
 /*
+ * Stores current CPU being used by cifsd.
+ * Updated after succesfully spawning a new cifsd thread.
+ */
+static int cifsd_cur_cpu;
+/*
+ * Stores which CPUs have a cifsd thread running on it.
+ * Set/clear follows server->tsk lifetime.
+ */
+static struct cpumask cifsd_cpu_load;
+
+/*
  * Resolve hostname and set ip addr in tcp ses. Useful for hostnames that may
  * get their ip addresses changed at some point.
  *
@@ -1123,6 +1134,7 @@ clean_demultiplex_info(struct TCP_Server_Info *server)
 		 */
 	}
 
+	cpumask_clear_cpu(server->tsk_cpu, &cifsd_cpu_load);
 	put_net(cifs_net_ns(server));
 	kfree(server->leaf_fullpath);
 	kfree(server->hostname);
@@ -1722,8 +1734,57 @@ cifs_put_tcp_session(struct TCP_Server_Info *server, int from_reconnect)
 	server->session_key.len = 0;
 
 	task = xchg(&server->tsk, NULL);
-	if (task)
+	if (task) {
+		cpumask_clear_cpu(server->tsk_cpu, &cifsd_cpu_load);
 		send_sig(SIGKILL, task, 1);
+	}
+}
+
+static inline int cifsd_get_next_cpu(void)
+{
+	struct cpumask avail = {};
+	int cpu;
+
+	/* Try to get the next CPU without a cifsd instance. */
+	cpumask_andnot(&avail, cpu_online_mask, &cifsd_cpu_load);
+	if (cpumask_empty(&avail))
+		goto next_rr;
+
+	cpu = cpumask_next(cifsd_cur_cpu, &cifsd_cpu_load);
+	if (likely(cpu < nr_cpu_ids))
+		return cpu;
+next_rr:
+	/* All CPUs are running cifsd, just get the next round-robin. */
+	cpu = cpumask_next_wrap(cifsd_cur_cpu, cpu_online_mask);
+	if (likely(cpu < nr_cpu_ids))
+		return cpu;
+
+	/* Shouldn't reach as wrap above took care of returning something valid, but... */
+	return 0;
+}
+
+static int cifsd_start(struct TCP_Server_Info *server)
+{
+	int cpu, ret = 0;
+
+	/*
+	 * Since we're in a cifs function already, we know that this will succeed.
+	 * No need for try_module_get().
+	 */
+	__module_get(THIS_MODULE);
+	cpu = cifsd_get_next_cpu();
+	server->tsk = kthread_run_on_cpu(cifs_demultiplex_thread, server, cpu, "cifsd");
+	if (!IS_ERR(server->tsk)) {
+		cpumask_set_cpu(cifsd_cur_cpu, &cifsd_cpu_load);
+		server->tsk_cpu = cifsd_cur_cpu = cpu;
+	} else {
+		ret = PTR_ERR(server->tsk);
+		server->tsk = NULL;
+		cifs_dbg(VFS, "error %d create cifsd thread\n", ret);
+		module_put(THIS_MODULE);
+	}
+
+	return ret;
 }
 
 struct TCP_Server_Info *
@@ -1851,19 +1912,10 @@ cifs_get_tcp_session(struct smb3_fs_context *ctx,
 		goto out_err_crypto_release;
 	}
 smbd_connected:
-	/*
-	 * since we're in a cifs function already, we know that
-	 * this will succeed. No need for try_module_get().
-	 */
-	__module_get(THIS_MODULE);
-	tcp_ses->tsk = kthread_run(cifs_demultiplex_thread,
-				  tcp_ses, "cifsd");
-	if (IS_ERR(tcp_ses->tsk)) {
-		rc = PTR_ERR(tcp_ses->tsk);
-		cifs_dbg(VFS, "error %d create cifsd thread\n", rc);
-		module_put(THIS_MODULE);
+	rc = cifsd_start(tcp_ses);
+	if (rc)
 		goto out_err_crypto_release;
-	}
+
 	tcp_ses->min_offload = ctx->min_offload;
 	tcp_ses->retrans = ctx->retrans;
 	/*
@@ -1894,9 +1946,7 @@ smbd_connected:
 
 out_err_crypto_release:
 	cifs_crypto_secmech_release(tcp_ses);
-
 	put_net(cifs_net_ns(tcp_ses));
-
 out_err:
 	if (tcp_ses) {
 		if (SERVER_IS_CHAN(tcp_ses))