From: Stephen Hemminger <stephen@networkplumber.org>
Date: Fri, 26 Jan 2024 00:25:11 +0000 (-0800)
Subject: net/tun: use reciprocal_scale
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=3f3ebe53620818f6e9b029850cb47b96a4ac5b3b;p=linux.git

net/tun: use reciprocal_scale

Use the inline function reciprocal_scale rather than open coding
the scale optimization.  Also, remove unnecessary initializations.
Resulting compiled code is unchanged (according to godbolt).

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20240126002550.169608-1-stephen@networkplumber.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 4a4f8c8e79fa1..e335ece47dec7 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -54,6 +54,7 @@
 #include <linux/if_tun.h>
 #include <linux/if_vlan.h>
 #include <linux/crc32.h>
+#include <linux/math.h>
 #include <linux/nsproxy.h>
 #include <linux/virtio_net.h>
 #include <linux/rcupdate.h>
@@ -523,8 +524,7 @@ static inline void tun_flow_save_rps_rxhash(struct tun_flow_entry *e, u32 hash)
 static u16 tun_automq_select_queue(struct tun_struct *tun, struct sk_buff *skb)
 {
 	struct tun_flow_entry *e;
-	u32 txq = 0;
-	u32 numqueues = 0;
+	u32 txq, numqueues;
 
 	numqueues = READ_ONCE(tun->numqueues);
 
@@ -534,8 +534,7 @@ static u16 tun_automq_select_queue(struct tun_struct *tun, struct sk_buff *skb)
 		tun_flow_save_rps_rxhash(e, txq);
 		txq = e->queue_index;
 	} else {
-		/* use multiply and shift instead of expensive divide */
-		txq = ((u64)txq * numqueues) >> 32;
+		txq = reciprocal_scale(txq, numqueues);
 	}
 
 	return txq;