[ng_socket] Don't take the SOCKBUF_LOCK() twice in the RX data path.

[afedorov]

Summary

This is just a minor optimization, but it's sensitive. This gives an improvement of 30-50 kpps.

Description:
sbappendaddr() takes the lock internally.
sorwakeup() also takes the lock internally.
So, the lock is taken twice.

ngs_rcvmsg () already does this in the manner suggested by the patch.

Test Plan

We have been using these changes for over six months without any visible issues.

[kp]

I'm not particularly familiar with this code, but the patch does look correct to me.

sys/netgraph/ng_socket.c

1038–1040

That might want a comment to explain that sorwakeup_locked() releases the lock.

[afedorov]

Add a comment about locking.

[afedorov]

sys/netgraph/ng_socket.c

1038–1040

Yes, I thought about it)) While I'm here, add the same comment to ngs_rcvmsg().

[markj]

sys/netgraph/ng_socket.c

1032

Indentation on the second line should be by four spaces.

[afedorov]

Fix indentation.

[donner]

This patch seems to complicate things at the first glance.
But in the end, the sowakeup() call itself is the problem.
It requires to be called while holding the lock and releases it.

Usually lock should be hold as short as possible, so the function ngs_recmsg() seems to hold the lock unnecessary long. But there might be other races.

So, okay from me.

[vmaffione]

Not familiar with the code, but it looks ok to me.