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linux/include/net
Eric Dumazet f3483c8e1d net: rfs: hash function change
RFS is using two kinds of hash tables.

First one is controlled by /proc/sys/net/core/rps_sock_flow_entries = 2^N
and using the N low order bits of the l4 hash is good enough.

Then each RX queue has its own hash table, controlled by
/sys/class/net/eth1/queues/rx-$q/rps_flow_cnt = 2^X

Current hash function, using the X low order bits is suboptimal,
because RSS is usually using Func(hash) = (hash % power_of_two);

For example, with 32 RX queues, 6 low order bits have no entropy
for a given queue.

Switch this hash function to hash_32(hash, log) to increase
chances to use all possible slots and reduce collisions.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tom Herbert <tom@herbertland.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250321171309.634100-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2025-03-25 08:24:13 -07:00
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