net: cache for same cpu skb_attempt_defer_free

net: cache for same cpu skb_attempt_defer_free

Optimise skb_attempt_defer_free() when run by the same CPU the skb was
allocated on. Instead of __kfree_skb() -> kmem_cache_free() we can
disable softirqs and put the buffer into cpu local caches.

CPU bound TCP ping pong style benchmarking (i.e. netbench) showed a 1%
throughput increase (392.2 -> 396.4 Krps). Cross checking with profiles,
the total CPU share of skb_attempt_defer_free() dropped by 0.6%. Note,
I'd expect the win doubled with rx only benchmarks, as the optimisation
is for the receive path, but the test spends >55% of CPU doing writes.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/a887463fb219d973ec5ad275e31194812571f1f5.1712711977.git.asml.silence@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>