Messages in this thread | | | Date | Mon, 16 Jan 2023 14:41:40 +0100 | Subject | Re: [PATCH v3 4/4] virtio_net: disable cb aggressively | From | Laurent Vivier <> |
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Hi Michael,
On 5/26/21 10:24, Michael S. Tsirkin wrote: > There are currently two cases where we poll TX vq not in response to a > callback: start xmit and rx napi. We currently do this with callbacks > enabled which can cause extra interrupts from the card. Used not to be > a big issue as we run with interrupts disabled but that is no longer the > case, and in some cases the rate of spurious interrupts is so high > linux detects this and actually kills the interrupt. > > Fix up by disabling the callbacks before polling the tx vq. > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com> > --- > drivers/net/virtio_net.c | 16 ++++++++++++---- > 1 file changed, 12 insertions(+), 4 deletions(-) > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index c29f42d1e04f..a83dc038d8af 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -1433,7 +1433,10 @@ static void virtnet_poll_cleantx(struct receive_queue *rq) > return; > > if (__netif_tx_trylock(txq)) { > - free_old_xmit_skbs(sq, true); > + do { > + virtqueue_disable_cb(sq->vq); > + free_old_xmit_skbs(sq, true); > + } while (unlikely(!virtqueue_enable_cb_delayed(sq->vq))); > > if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS) > netif_tx_wake_queue(txq); > @@ -1605,12 +1608,17 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev) > struct netdev_queue *txq = netdev_get_tx_queue(dev, qnum); > bool kick = !netdev_xmit_more(); > bool use_napi = sq->napi.weight; > + unsigned int bytes = skb->len; > > /* Free up any pending old buffers before queueing new ones. */ > - free_old_xmit_skbs(sq, false); > + do { > + if (use_napi) > + virtqueue_disable_cb(sq->vq); > > - if (use_napi && kick) > - virtqueue_enable_cb_delayed(sq->vq); > + free_old_xmit_skbs(sq, false); > + > + } while (use_napi && kick && > + unlikely(!virtqueue_enable_cb_delayed(sq->vq))); > > /* timestamp packet in software */ > skb_tx_timestamp(skb);
This patch seems to introduce a problem with QEMU connected to passt using netdev stream backend.
When I run an iperf3 test I get after 1 or 2 seconds of test:
[ 254.035559] NETDEV WATCHDOG: ens3 (virtio_net): transmit queue 0 timed out ... [ 254.060962] virtio_net virtio1 ens3: TX timeout on queue: 0, sq: output.0, vq: 0x1, name: output.0, 8856000 usecs ago [ 259.155150] virtio_net virtio1 ens3: TX timeout on queue: 0, sq: output.0, vq: 0x1, name: output.0, 13951000 usecs ago
In QEMU, I can see in virtio_net_tx_bh() the function virtio_net_flush_tx() has flushed all the queue entries and re-enabled the queue notification with virtio_queue_set_notification() and tries to flush again the queue and as it is empty it does nothing more and then rely on a kernel notification to re-enable the bottom half function. As this notification never comes the queue is stuck and kernel add entries but QEMU doesn't remove them:
2812 static void virtio_net_tx_bh(void *opaque) 2813 { ... 2833 ret = virtio_net_flush_tx(q);
-> flush the queue and ret is not an error and not n->tx_burst (that would re-schedule the function)
... 2850 virtio_queue_set_notification(q->tx_vq, 1);
-> re-enable the queue notification
2851 ret = virtio_net_flush_tx(q); 2852 if (ret == -EINVAL) { 2853 return; 2854 } else if (ret > 0) { 2855 virtio_queue_set_notification(q->tx_vq, 0); 2856 qemu_bh_schedule(q->tx_bh); 2857 q->tx_waiting = 1; 2858 }
-> ret is 0, exit the function without re-scheduling the function. ... 2859 }
If I revert this patch in the kernel (a7766ef18b33 ("virtio_net: disable cb aggressively")), it works fine.
How to reproduce it:
I start passt (https://passt.top/passt):
passt -f
and then QEMU
qemu-system-x86_64 ... --netdev stream,id=netdev0,server=off,addr.type=unix,addr.path=/tmp/passt_1.socket -device virtio-net,mac=9a:2b:2c:2d:2e:2f,netdev=netdev0
Host side:
sysctl -w net.core.rmem_max=134217728 sysctl -w net.core.wmem_max=134217728 iperf3 -s
Guest side:
sysctl -w net.core.rmem_max=536870912 sysctl -w net.core.wmem_max=536870912
ip link set dev $DEV mtu 256 iperf3 -c $HOST -t10 -i0 -Z -P 8 -l 1M --pacing-timer 1000000 -w 4M
Any idea of what is the problem?
Thanks, Laurent
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