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 4a4f8c8e79fa12dc84a8c83cefbf964dd40e1aa2..e335ece47dec791c8fe82f11845950f3867d1836 100644 (file)
--- 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;