From c13f7e1a94007c4381814e7daf033e3e8f0663f3 Mon Sep 17 00:00:00 2001 From: Lars Ellenberg Date: Fri, 29 Oct 2010 23:32:01 +0200 Subject: [PATCH] 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 Signed-off-by: Lars Ellenberg --- drivers/block/drbd/drbd_receiver.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c index 89d8a7cc4054..24487d4fb202 100644 --- a/drivers/block/drbd/drbd_receiver.c +++ b/drivers/block/drbd/drbd_receiver.c @@ -3627,17 +3627,19 @@ static void drbdd(struct drbd_conf *mdev) } shs = drbd_cmd_handler[cmd].pkt_size - sizeof(union p_header); - 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; } + 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; + } + } + rv = drbd_cmd_handler[cmd].function(mdev, cmd, packet_size - shs); if (unlikely(!rv)) { -- 2.20.1