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authorLars Ellenberg <lars.ellenberg@linbit.com>2010-10-29 23:32:01 +0200
committerJens Axboe <jaxboe@fusionio.com>2010-11-27 19:50:43 +0100
commitc13f7e1a94007c4381814e7daf033e3e8f0663f3 (patch)
tree38115a45b39cd53204268238b8dc6e5bbfd9bafc /drivers/block
parent19650e8580987c0ffabc2fe2cbc16b944789df8b (diff)
downloadop-kernel-dev-c13f7e1a94007c4381814e7daf033e3e8f0663f3.zip
op-kernel-dev-c13f7e1a94007c4381814e7daf033e3e8f0663f3.tar.gz
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>
Diffstat (limited to 'drivers/block')
-rw-r--r--drivers/block/drbd/drbd_receiver.c14
1 files changed, 8 insertions, 6 deletions
diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index 89d8a7c..24487d4 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)) {
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