Commit fdaa767a authored Dec 07, 2017 by Toshiaki Makita Committed by David S. Miller Dec 08, 2017

virtio_net: Disable interrupts if napi_complete_done rescheduled napi



Since commit 39e6c820 ("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 cbdadbbf ("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

Signed-off-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 62cd2770

drivers/net/virtio_net.c

+6 −3

Original line number	Diff line number	Diff line
		@@ -261,9 +261,12 @@ static void virtqueue_napi_complete(struct napi_struct *napi,
		int opaque;

		opaque = virtqueue_enable_cb_prepare(vq);
		if (napi_complete_done(napi, processed) &&
		unlikely(virtqueue_poll(vq, opaque)))
		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)

Admin message