net: avoid a pair of dst_hold()/dst_release() in ip_push_pending_frames()
We can reduce pressure on dst entry refcount that slowdown UDP transmit path on SMP machines. This pressure is visible on RTP servers when delivering content to mediagateways, especially big ones, handling thousand of streams. Several cpus send UDP frames to the same destination, hence use the same dst entry. This patch makes ip_push_pending_frames() steal the refcount its callers had to take when filling inet->cork.dst. This doesnt avoid all refcounting, but still gives speedups on SMP, on UDP/RAW transmit path. Signed-off-by: NEric Dumazet <dada1@cosmosbay.com> Signed-off-by: NDavid S. Miller <davem@davemloft.net>
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