Commit 37b0ea8f authored by Eric Dumazet's avatar Eric Dumazet Committed by Jakub Kicinski
Browse files

net: expand NETDEV_RSS_KEY_LEN to 256 bytes 



NETDEV_RSS_KEY_LEN has been set to 52 bytes in 2014, until now.

Jakub suggested we bump the size to 128 bytes or more.

Some drivers (like idpf) were already working around the core limit.

Since this change might cause some issues in admin scripts,
bump it directly to 256 in one go.

tjbp26:~# cat /proc/sys/net/core/netdev_rss_key | wc -c
768

tjbp26:~# ethtool -x eth1
RX flow hash indirection table for eth1 with 32 RX ring(s):
...
RSS hash key:
fe:16:5b:2f:93:85:c2:c9:c1:ef:bd:60:c6:e0:2b:99:4d:bf:b7:14:c8:1e:8d:cb:31:17:51:da:55:eb:91:d9:9e:f9:89:9b:44:a1:dc:08:72:3a:b3:d6:31:86:9a:fe:02:3a:0d:eb:a1:7c:f5:a3:51:3b:08:56:c9:3f:71:69:01:ba:70:38
RSS hash function:
    toeplitz: on
    xor: off
    crc32: off

Suggested-by: default avatarJakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/netdev/20260122075206.504ec591@kernel.org/


Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reviewed-by: default avatarWillem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20260122190349.2771064-1-edumazet@google.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent a113a8ac

Documentation/admin-guide/sysctl/net.rst

+7 −6
Original line number Diff line number Diff line
@@ -314,21 +314,22 @@ Default: 1000 
netdev_rss_key

--------------



RSS (Receive Side Scaling) enabled drivers use a 40 bytes host key that is

randomly generated.

RSS (Receive Side Scaling) enabled drivers use a host key that

is randomly generated.

Some user space might need to gather its content even if drivers do not

provide ethtool -x support yet.



::



  myhost:~# cat /proc/sys/net/core/netdev_rss_key

  84:50:f4:00:a8:15:d1:a7:e9:7f:1d:60:35:c7:47:25:42:97:74:ca:56:bb:b6:a1:d8: ... (52 bytes total)

  84:50:f4:00:a8:15:d1:a7:e9:7f:1d:60:35:c7:47:25:42:97:74:ca:56:bb:b6:a1:d8: ... (256 bytes total)



File contains nul bytes if no driver ever called netdev_rss_key_fill() function.

File contains all nul bytes if no driver ever called netdev_rss_key_fill()

function.



Note:

  /proc/sys/net/core/netdev_rss_key contains 52 bytes of key,

  but most drivers only use 40 bytes of it.

  /proc/sys/net/core/netdev_rss_key contains 256 bytes of key,

  but many drivers only use 40 or 52 bytes of it.



::

include/linux/netdevice.h

+1 −2
Original line number Diff line number Diff line
@@ -5166,8 +5166,7 @@ void *netdev_lower_dev_get_private(struct net_device *dev, 
void netdev_lower_state_changed(struct net_device *lower_dev,

				void *lower_state_info);



/* RSS keys are 40 or 52 bytes long */

#define NETDEV_RSS_KEY_LEN 52

#define NETDEV_RSS_KEY_LEN 256

extern u8 netdev_rss_key[NETDEV_RSS_KEY_LEN] __read_mostly;

void netdev_rss_key_fill(void *buffer, size_t len);

net/core/sysctl_net_core.c

+8 −2
Original line number Diff line number Diff line
@@ -325,10 +325,16 @@ static int proc_do_dev_weight(const struct ctl_table *table, int write, 
static int proc_do_rss_key(const struct ctl_table *table, int write,

			   void *buffer, size_t *lenp, loff_t *ppos)

{

	struct ctl_table fake_table;

	char buf[NETDEV_RSS_KEY_LEN * 3];

	struct ctl_table fake_table;

	char *pos = buf;



	for (int i = 0; i < NETDEV_RSS_KEY_LEN; i++) {

		pos = hex_byte_pack(pos, netdev_rss_key[i]);

		*pos++ = ':';

	}

	*(--pos) = 0;



	snprintf(buf, sizeof(buf), "%*phC", NETDEV_RSS_KEY_LEN, netdev_rss_key);

	fake_table.data = buf;

	fake_table.maxlen = sizeof(buf);

	return proc_dostring(&fake_table, write, buffer, lenp, ppos);