SUNRPC: Optimise transport balancing code

Moves the balancing code to avoid doing cursor changes on every search
iteration.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

diff --git a/net/sunrpc/xprtmultipath.c b/net/sunrpc/xprtmultipath.c
index f3ecd0bee4840bb783436146101cabe6ec98ff98..78c075a68c0479060869aab8355470a88dfe5e2c 100644 (file)
--- a/net/sunrpc/xprtmultipath.c
+++ b/net/sunrpc/xprtmultipath.c
@@ -19,7 +19,7 @@
 #include <linux/sunrpc/addr.h>
 #include <linux/sunrpc/xprtmultipath.h>
 
-typedef struct rpc_xprt *(*xprt_switch_find_xprt_t)(struct list_head *head,
+typedef struct rpc_xprt *(*xprt_switch_find_xprt_t)(struct rpc_xprt_switch *xps,
                const struct rpc_xprt *cur);
 
 static const struct rpc_xprt_iter_ops rpc_xprt_iter_singular;
@@ -291,22 +291,15 @@ struct rpc_xprt *xprt_switch_find_next_entry(struct list_head *head,
 }
 
 static
-struct rpc_xprt *xprt_switch_set_next_cursor(struct list_head *head,
+struct rpc_xprt *xprt_switch_set_next_cursor(struct rpc_xprt_switch *xps,
                struct rpc_xprt **cursor,
                xprt_switch_find_xprt_t find_next)
 {
-       struct rpc_xprt *cur, *pos, *old;
+       struct rpc_xprt *pos, *old;
 
-       cur = READ_ONCE(*cursor);
-       for (;;) {
-               old = cur;
-               pos = find_next(head, old);
-               if (pos == NULL)
-                       break;
-               cur = cmpxchg_relaxed(cursor, old, pos);
-               if (cur == old)
-                       break;
-       }
+       old = smp_load_acquire(cursor);
+       pos = find_next(xps, old);
+       smp_store_release(cursor, pos);
        return pos;
 }
 
@@ -318,13 +311,11 @@ struct rpc_xprt *xprt_iter_next_entry_multiple(struct rpc_xprt_iter *xpi,
 
        if (xps == NULL)
                return NULL;
-       return xprt_switch_set_next_cursor(&xps->xps_xprt_list,
-                       &xpi->xpi_cursor,
-                       find_next);
+       return xprt_switch_set_next_cursor(xps, &xpi->xpi_cursor, find_next);
 }
 
 static
-struct rpc_xprt *xprt_switch_find_next_entry_roundrobin(struct list_head *head,
+struct rpc_xprt *__xprt_switch_find_next_entry_roundrobin(struct list_head *head,
                const struct rpc_xprt *cur)
 {
        struct rpc_xprt *ret;
@@ -336,31 +327,49 @@ struct rpc_xprt *xprt_switch_find_next_entry_roundrobin(struct list_head *head,
 }
 
 static
-struct rpc_xprt *xprt_iter_next_entry_roundrobin(struct rpc_xprt_iter *xpi)
+struct rpc_xprt *xprt_switch_find_next_entry_roundrobin(struct rpc_xprt_switch *xps,
+               const struct rpc_xprt *cur)
 {
-       struct rpc_xprt_switch *xps = rcu_dereference(xpi->xpi_xpswitch);
+       struct list_head *head = &xps->xps_xprt_list;
        struct rpc_xprt *xprt;
-       unsigned long xprt_queuelen;
-       unsigned long xps_queuelen;
+       unsigned int nactive;
 
-       do {
-               xprt = xprt_iter_next_entry_multiple(xpi,
-                       xprt_switch_find_next_entry_roundrobin);
-               if (xprt == NULL)
+       for (;;) {
+               unsigned long xprt_queuelen, xps_queuelen;
+
+               xprt = __xprt_switch_find_next_entry_roundrobin(head, cur);
+               if (!xprt)
                        break;
                xprt_queuelen = atomic_long_read(&xprt->queuelen);
-               if (xprt_queuelen <= 2)
-                       break;
                xps_queuelen = atomic_long_read(&xps->xps_queuelen);
+               nactive = READ_ONCE(xps->xps_nactive);
                /* Exit loop if xprt_queuelen <= average queue length */
-       } while (xprt_queuelen * READ_ONCE(xps->xps_nactive) > xps_queuelen);
+               if (xprt_queuelen * nactive <= xps_queuelen)
+                       break;
+               cur = xprt;
+       }
        return xprt;
 }
 
+static
+struct rpc_xprt *xprt_iter_next_entry_roundrobin(struct rpc_xprt_iter *xpi)
+{
+       return xprt_iter_next_entry_multiple(xpi,
+                       xprt_switch_find_next_entry_roundrobin);
+}
+
+static
+struct rpc_xprt *xprt_switch_find_next_entry_all(struct rpc_xprt_switch *xps,
+               const struct rpc_xprt *cur)
+{
+       return xprt_switch_find_next_entry(&xps->xps_xprt_list, cur);
+}
+
 static
 struct rpc_xprt *xprt_iter_next_entry_all(struct rpc_xprt_iter *xpi)
 {
-       return xprt_iter_next_entry_multiple(xpi, xprt_switch_find_next_entry);
+       return xprt_iter_next_entry_multiple(xpi,
+                       xprt_switch_find_next_entry_all);
 }
 
 /*