tree 38115a45b39cd53204268238b8dc6e5bbfd9bafc
parent 19650e8580987c0ffabc2fe2cbc16b944789df8b
author Lars Ellenberg <lars.ellenberg@linbit.com> 1288387921 +0200
committer Jens Axboe <jaxboe@fusionio.com> 1290883843 +0100

drbd: don't recvmsg with zero length

This should fix a performance degradation we observed recently.

If we don't expect any subheader, we should not call into the tcp stack,
as that may add considerable latency if there is no data available at
this point.

For a synthetic synchronous write load with single outstanding writes,
this additional latency when processing the "unplug remote" packet
added up to a performance degradation factor >= 10.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>