[PATCH] net/tun: use reciprocal_scale

[PATCH] net/tun: use reciprocal_scale

[Stephen Hemminger]

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>
---
 drivers/net/tun.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 4a4f8c8e79fa..e335ece47dec 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;
-- 
2.43.0

Re: [PATCH] net/tun: use reciprocal_scale

[Willem de Bruijn]

Stephen Hemminger wrote:
> 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>

Targeting net-next

Reviewed-by: Willem de Bruijn <willemb@google.com>

Re: [PATCH] net/tun: use reciprocal_scale

[Jason Wang]

On Fri, Jan 26, 2024 at 8:26 AM Stephen Hemminger
<stephen@networkplumber.org> wrote:
>
> 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>

Acked-by: Jason Wang <jasowang@redhat.com>

Thanks

Re: [PATCH] net/tun: use reciprocal_scale

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Paolo Abeni <pabeni@redhat.com>:

On Thu, 25 Jan 2024 16:25:11 -0800 you wrote:
> 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>
> ---
>  drivers/net/tun.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)

Here is the summary with links:
  - net/tun: use reciprocal_scale
    https://git.kernel.org/netdev/net-next/c/3f3ebe536208

You are awesome, thank you!
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