Gh0st
/
linux
mirror of https://github.com/torvalds/linux.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

net: optimize eth_type_trans() vs CONFIG_STACKPROTECTOR_STRONG=y 

Some platforms exhibit very high costs with CONFIG_STACKPROTECTOR_STRONG=y
when a function needs to pass the address of a local variable to external
functions.

eth_type_trans() (and its callers) is showing this anomaly on AMD EPYC 7B12
platforms (and maybe others).

We could :

1) inline eth_type_trans()

   This would help if its callers also has the same issue, and the canary cost
   would be paid by the callers already.

   This is a bit cumbersome because netdev_uses_dsa() is pulling
   whole <net/dsa.h> definitions.

2) Compile net/ethernet/eth.c with -fno-stack-protector

   This would weaken security.

3) Hack eth_type_trans() to temporarily use skb->dev as a place holder
   if skb_header_pointer() needs to pull 2 bytes not present in skb->head.

This patch implements 3), and brings a 5% improvement on TX/RX intensive
workload (tcp_rr 10,000 flows) on AMD EPYC 7B12.

Removing CONFIG_STACKPROTECTOR_STRONG on this platform can improve
performance by 25 %.
This means eth_type_trans() issue is not an isolated artifact.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20251121061725.206675-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet 2025-11-21 06:17:25 +00:00 committed by Jakub Kicinski
parent e254c212cd
commit ec1e48e97f
1 changed files with 8 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
net/ethernet/eth.c
View File

@ -154,9 +154,9 @@ EXPORT_SYMBOL(eth_get_headlen);
*/ */
__be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev) __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev)
{ {
unsigned short _service_access_point;
const unsigned short *sap; const unsigned short *sap;
const struct ethhdr *eth; const struct ethhdr *eth;
__be16 res;
skb->dev = dev; skb->dev = dev;
skb_reset_mac_header(skb); skb_reset_mac_header(skb);
@ -181,15 +181,15 @@ __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev)
* the protocol design and runs IPX over 802.3 without an 802.2 LLC * the protocol design and runs IPX over 802.3 without an 802.2 LLC
* layer. We look for FFFF which isn't a used 802.2 SSAP/DSAP. This * layer. We look for FFFF which isn't a used 802.2 SSAP/DSAP. This
* won't work for fault tolerant netware but does for the rest. * won't work for fault tolerant netware but does for the rest.
* We use skb->dev as temporary storage to not hit
* CONFIG_STACKPROTECTOR_STRONG=y costs on some platforms.
*/ */
sap = skb_header_pointer(skb, 0, sizeof(*sap), &_service_access_point); sap = skb_header_pointer(skb, 0, sizeof(*sap), &skb->dev);
if (sap && *sap == 0xFFFF) res = (sap && *sap == 0xFFFF) ? htons(ETH_P_802_3) : htons(ETH_P_802_2);
return htons(ETH_P_802_3);
/* /* restore skb->dev in case it was mangled by skb_header_pointer(). */
* Real 802.2 LLC skb->dev = dev;
*/ return res;
return htons(ETH_P_802_2);
} }
EXPORT_SYMBOL(eth_type_trans); EXPORT_SYMBOL(eth_type_trans);