Commit c13f7e1a authored by Lars Ellenberg's avatar Lars Ellenberg Committed by Jens Axboe

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: default avatarPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: default avatarLars Ellenberg <lars.ellenberg@linbit.com>
parent 19650e85
......@@ -3627,15 +3627,17 @@ static void drbdd(struct drbd_conf *mdev)
}
shs = drbd_cmd_handler[cmd].pkt_size - sizeof(union p_header);
if (packet_size - shs > 0 && !drbd_cmd_handler[cmd].expect_payload) {
dev_err(DEV, "No payload expected %s l:%d\n", cmdname(cmd), packet_size);
goto err_out;
}
if (shs) {
rv = drbd_recv(mdev, &header->h80.payload, shs);
if (unlikely(rv != shs)) {
dev_err(DEV, "short read while reading sub header: rv=%d\n", rv);
goto err_out;
}
if (packet_size - shs > 0 && !drbd_cmd_handler[cmd].expect_payload) {
dev_err(DEV, "No payload expected %s l:%d\n", cmdname(cmd), packet_size);
goto err_out;
}
rv = drbd_cmd_handler[cmd].function(mdev, cmd, packet_size - shs);
......
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