SUNRPC: Remove the .svo_enqueue_xprt method

We have never been able to track down and address the underlying
cause of the performance issues with workqueue-based service
support. svo_enqueue_xprt is called multiple times per RPC, so
it adds instruction path length, but always ends up at the same
function: svc_xprt_do_enqueue(). We do not anticipate needing
this flexibility for dynamic nfsd thread management support.

As a micro-optimization, remove .svo_enqueue_xprt because
Spectre/Meltdown makes virtual function calls more costly.

This change essentially reverts commit b9e13cdf ("nfsd/sunrpc:
turn enqueueing a svc_xprt into a svc_serv operation").
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/lockd/svc.c

@@ -353,7 +353,6 @@ static struct notifier_block lockd_inet6addr_notifier = {
 static const struct svc_serv_ops lockd_sv_ops = {
 	.svo_shutdown		= svc_rpcb_cleanup,
 	.svo_function		= lockd,
-	.svo_enqueue_xprt	= svc_xprt_do_enqueue,
 	.svo_module		= THIS_MODULE,
 };
 

fs/nfs/callback.c

@@ -234,13 +234,11 @@ static int nfs_callback_up_net(int minorversion, struct svc_serv *serv,
 
 static const struct svc_serv_ops nfs40_cb_sv_ops = {
 	.svo_function		= nfs4_callback_svc,
-	.svo_enqueue_xprt	= svc_xprt_do_enqueue,
 	.svo_module		= THIS_MODULE,
 };
 #if defined(CONFIG_NFS_V4_1)
 static const struct svc_serv_ops nfs41_cb_sv_ops = {
 	.svo_function		= nfs41_callback_svc,
-	.svo_enqueue_xprt	= svc_xprt_do_enqueue,
 	.svo_module		= THIS_MODULE,
 };
 

fs/nfsd/nfssvc.c

@@ -615,7 +615,6 @@ static int nfsd_get_default_max_blksize(void)
 static const struct svc_serv_ops nfsd_thread_sv_ops = {
 	.svo_shutdown		= nfsd_last_thread,
 	.svo_function		= nfsd,
-	.svo_enqueue_xprt	= svc_xprt_do_enqueue,
 	.svo_module		= THIS_MODULE,
 };
 

include/linux/sunrpc/svc.h

@@ -61,9 +61,6 @@ struct svc_serv_ops {
 	/* function for service threads to run */
 	int		(*svo_function)(void *);
 
-	/* queue up a transport for servicing */
-	void		(*svo_enqueue_xprt)(struct svc_xprt *);
-
 	/* optional module to count when adding threads.
 	 * Thread function must call module_put_and_kthread_exit() to exit.
 	 */

include/linux/sunrpc/svc_xprt.h

@@ -131,7 +131,6 @@ int	svc_create_xprt(struct svc_serv *, const char *, struct net *,
 			const int, const unsigned short, int,
 			const struct cred *);
 void	svc_xprt_received(struct svc_xprt *xprt);
-void	svc_xprt_do_enqueue(struct svc_xprt *xprt);
 void	svc_xprt_enqueue(struct svc_xprt *xprt);
 void	svc_xprt_put(struct svc_xprt *xprt);
 void	svc_xprt_copy_addrs(struct svc_rqst *rqstp, struct svc_xprt *xprt);

net/sunrpc/svc_xprt.c

@@ -32,6 +32,7 @@ static int svc_deferred_recv(struct svc_rqst *rqstp);
 static struct cache_deferred_req *svc_defer(struct cache_req *req);
 static void svc_age_temp_xprts(struct timer_list *t);
 static void svc_delete_xprt(struct svc_xprt *xprt);
+static void svc_xprt_do_enqueue(struct svc_xprt *xprt);
 
 /* apparently the "standard" is that clients close
  * idle connections after 5 minutes, servers after
@@ -266,12 +267,12 @@ void svc_xprt_received(struct svc_xprt *xprt)
 	}
 
 	/* As soon as we clear busy, the xprt could be closed and
-	 * 'put', so we need a reference to call svc_enqueue_xprt with:
+	 * 'put', so we need a reference to call svc_xprt_do_enqueue with:
 	 */
 	svc_xprt_get(xprt);
 	smp_mb__before_atomic();
 	clear_bit(XPT_BUSY, &xprt->xpt_flags);
-	xprt->xpt_server->sv_ops->svo_enqueue_xprt(xprt);
+	svc_xprt_do_enqueue(xprt);
 	svc_xprt_put(xprt);
 }
 EXPORT_SYMBOL_GPL(svc_xprt_received);
@@ -423,7 +424,7 @@ static bool svc_xprt_ready(struct svc_xprt *xprt)
 	return false;
 }
 
-void svc_xprt_do_enqueue(struct svc_xprt *xprt)
+static void svc_xprt_do_enqueue(struct svc_xprt *xprt)
 {
 	struct svc_pool *pool;
 	struct svc_rqst	*rqstp = NULL;
@@ -467,7 +468,6 @@ void svc_xprt_do_enqueue(struct svc_xprt *xprt)
 	put_cpu();
 	trace_svc_xprt_enqueue(xprt, rqstp);
 }
-EXPORT_SYMBOL_GPL(svc_xprt_do_enqueue);
 
 /*
  * Queue up a transport with data pending. If there are idle nfsd
@@ -478,7 +478,7 @@ void svc_xprt_enqueue(struct svc_xprt *xprt)
 {
 	if (test_bit(XPT_BUSY, &xprt->xpt_flags))
 		return;
-	xprt->xpt_server->sv_ops->svo_enqueue_xprt(xprt);
+	svc_xprt_do_enqueue(xprt);
 }
 EXPORT_SYMBOL_GPL(svc_xprt_enqueue);