Patch "virtio_net: Disable interrupts if napi_complete_done rescheduled napi" has been added to the 4.15-stable tree

This is a note to let you know that I've just added the patch titled

virtio_net: Disable interrupts if napi_complete_done rescheduled napi

to the 4.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
virtio_net-disable-interrupts-if-napi_complete_done-rescheduled-napi.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Toshiaki Makita <[email protected]>
Date: Thu, 7 Dec 2017 13:15:15 +0900
Subject: virtio_net: Disable interrupts if napi_complete_done rescheduled napi

From: Toshiaki Makita <[email protected]>

[ Upstream commit fdaa767aefc1685f9a41e91f447c9aea94103df6 ]

Since commit 39e6c8208d7b ("net: solve a NAPI race") napi has been able to be rescheduled within napi_complete_done() even in non-busypoll case, but virtnet_poll() always enabled interrupts before complete, and when napi was rescheduled within napi_complete_done() it did not disable interrupts.
This caused more interrupts when event idx is disabled.

According to commit cbdadbbf0c79 ("virtio_net: fix race in RX VQ processing") we cannot place virtqueue_enable_cb_prepare() after NAPI_STATE_SCHED is cleared, so disable interrupts again if napi_complete_done() returned false.

Tested with vhost-user of OVS 2.7 on host, which does not have the event idx feature.

* Before patch:

$ netperf -t UDP_STREAM -H 192.168.150.253 -l 60 -- -m 1472
MIGRATED UDP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.150.253 () port 0 AF_INET
Socket  Message  Elapsed      Messages
Size    Size     Time         Okay Errors   Throughput
bytes   bytes    secs            #      #   10^6bits/sec

212992    1472   60.00     32763206      0    6430.32
212992           60.00     23384299           4589.56

Interrupts on guest: 9872369
Packets/interrupt:   2.37

* After patch

$ netperf -t UDP_STREAM -H 192.168.150.253 -l 60 -- -m 1472
MIGRATED UDP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.150.253 () port 0 AF_INET
Socket  Message  Elapsed      Messages
Size    Size     Time         Okay Errors   Throughput
bytes   bytes    secs            #      #   10^6bits/sec

212992    1472   60.00     32794646      0    6436.49
212992           60.00     32793501           6436.27

Interrupts on guest: 4941299
Packets/interrupt:   6.64

---
 drivers/net/virtio_net.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

@@ -261,9 +261,12 @@ static void virtqueue_napi_complete(stru
 	int opaque;
 
 	opaque = virtqueue_enable_cb_prepare(vq);
-	if (napi_complete_done(napi, processed) &&
-	    unlikely(virtqueue_poll(vq, opaque)))
-		virtqueue_napi_schedule(napi, vq);
+	if (napi_complete_done(napi, processed)) {
+		if (unlikely(virtqueue_poll(vq, opaque)))
+			virtqueue_napi_schedule(napi, vq);
+	} else {
+		virtqueue_disable_cb(vq);
+	}
 }
 
 static void skb_xmit_done(struct virtqueue *vq)

Patches currently in stable-queue which might be from [email protected] are

queue-4.15/virtio_net-disable-interrupts-if-napi_complete_done-rescheduled-napi.patch