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net: expand NETDEV_RSS_KEY_LEN to 256 bytes

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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: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/netdev/20260122075206.504ec591@kernel.org/
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20260122190349.2771064-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet
2026-01-22 19:03:49 +00:00
committed by Jakub Kicinski
parent a113a8ac50
commit 37b0ea8fef
3 changed files with 16 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

13
Documentation/admin-guide/sysctl/net.rst
View File

@@ -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.
::

3
include/linux/netdevice.h
View File

@@ -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);

10
net/core/sysctl_net_core.c
View File

@@ -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);