Backported from X.org:

 commit 9bf46610a9d20962854016032de4567974e87957
 Author: Chris Wilson <chris@chris-wilson.co.uk>
 Date:   Fri Jun 21 22:58:31 2013 +0100

    os: Immediately queue initial WriteToClient

    If we immediately put the WriteToClient() buffer into the socket's write
    queue, not only do we benefit from sending the response back to client
    earlier, but we also avoid the overhead of copying the data into our own
    staging buffer and causing extra work in the next select(). The write is
    effectively free as typically we may only send one reply per client per
    select() call, so the cost of the FlushClient() is the same.

    shmget10:   26400 -> 110000
    getimage10: 25000 -> 108000

    shmget500:   3160 -> 13500
    getimage500: 1000 -> 1010

    The knock-on effect is that on a mostly idle composited desktop, the CPU
    overhead is dominated by the memmove in WriteToClient, which is in turn
    eliminated by this patch.
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Backported-to-NX-by: Mike Gabriel <mike.gabriel@das-netzwerkteam.de>