* Re: [PATCH netdev] virtio-net: support XDP_TX when not more queues
2021-02-10 21:40 ` [PATCH netdev] virtio-net: support XDP_TX when not more queues Michael S. Tsirkin
@ 2021-02-11 11:00 ` Jesper Dangaard Brouer
2021-02-18 2:18 ` Jason Wang
1 sibling, 0 replies; 3+ messages in thread
From: Jesper Dangaard Brouer @ 2021-02-11 11:00 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: Xuan Zhuo, Jesper Dangaard Brouer, Daniel Borkmann, netdev,
John Fastabend, Alexei Starovoitov, virtualization, Marek Majtyka,
dust.li, brouer, Jakub Kicinski, bpf, David S. Miller
On Wed, 10 Feb 2021 16:40:41 -0500
"Michael S. Tsirkin" <mst@redhat.com> wrote:
> On Wed, Jan 13, 2021 at 04:08:57PM +0800, Xuan Zhuo wrote:
> > The number of queues implemented by many virtio backends is limited,
> > especially some machines have a large number of CPUs. In this case, it
> > is often impossible to allocate a separate queue for XDP_TX.
> >
> > This patch allows XDP_TX to run by reuse the existing SQ with
> > __netif_tx_lock() hold when there are not enough queues.
I'm a little puzzled about the choice of using the netdevice TXQ
lock __netif_tx_lock() / __netif_tx_unlock().
Can you explain more about this choice?
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
>
> I'd like to get some advice on whether this is ok from some
> XDP experts - previously my understanding was that it is
> preferable to disable XDP for such devices than
> use locks on XDP fast path.
I think it is acceptable, because the ndo_xdp_xmit / virtnet_xdp_xmit
takes a bulk of packets (currently 16).
Some drivers already does this.
It would have been nice if we could set a feature flag, that allow
users to see that this driver uses locking in the XDP transmit
(ndo_xdp_xmit) function call... but it seems like a pipe dream :-P
Code related to the locking
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index ba8e637..7a3b2a7 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
[...]
> > @@ -481,14 +484,34 @@ static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
> > return 0;
> > }
> >
> > -static struct send_queue *virtnet_xdp_sq(struct virtnet_info *vi)
> > +static struct send_queue *virtnet_get_xdp_sq(struct virtnet_info *vi)
> > {
> > unsigned int qp;
> > + struct netdev_queue *txq;
> > +
> > + if (vi->curr_queue_pairs > nr_cpu_ids) {
> > + qp = vi->curr_queue_pairs - vi->xdp_queue_pairs + smp_processor_id();
> > + } else {
> > + qp = smp_processor_id() % vi->curr_queue_pairs;
> > + txq = netdev_get_tx_queue(vi->dev, qp);
> > + __netif_tx_lock(txq, raw_smp_processor_id());
> > + }
> >
> > - qp = vi->curr_queue_pairs - vi->xdp_queue_pairs + smp_processor_id();
> > return &vi->sq[qp];
> > }
> >
> > +static void virtnet_put_xdp_sq(struct virtnet_info *vi)
> > +{
> > + unsigned int qp;
> > + struct netdev_queue *txq;
> > +
> > + if (vi->curr_queue_pairs <= nr_cpu_ids) {
> > + qp = smp_processor_id() % vi->curr_queue_pairs;
> > + txq = netdev_get_tx_queue(vi->dev, qp);
> > + __netif_tx_unlock(txq);
> > + }
> > +}
> > +
> > static int virtnet_xdp_xmit(struct net_device *dev,
> > int n, struct xdp_frame **frames, u32 flags)
> > {
> > @@ -512,7 +535,7 @@ static int virtnet_xdp_xmit(struct net_device *dev,
> > if (!xdp_prog)
> > return -ENXIO;
> >
> > - sq = virtnet_xdp_sq(vi);
> > + sq = virtnet_get_xdp_sq(vi);
> >
> > if (unlikely(flags & ~XDP_XMIT_FLAGS_MASK)) {
> > ret = -EINVAL;
> > @@ -560,12 +583,13 @@ static int virtnet_xdp_xmit(struct net_device *dev,
> > sq->stats.kicks += kicks;
> > u64_stats_update_end(&sq->stats.syncp);
> >
> > + virtnet_put_xdp_sq(vi);
> > return ret;
> > }
> >
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
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^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH netdev] virtio-net: support XDP_TX when not more queues
2021-02-10 21:40 ` [PATCH netdev] virtio-net: support XDP_TX when not more queues Michael S. Tsirkin
2021-02-11 11:00 ` Jesper Dangaard Brouer
@ 2021-02-18 2:18 ` Jason Wang
1 sibling, 0 replies; 3+ messages in thread
From: Jason Wang @ 2021-02-18 2:18 UTC (permalink / raw)
To: Michael S. Tsirkin, Xuan Zhuo
Cc: Jesper Dangaard Brouer, Daniel Borkmann, netdev, John Fastabend,
Alexei Starovoitov, virtualization, dust.li, Jakub Kicinski, bpf,
David S. Miller
On 2021/2/11 5:40 上午, Michael S. Tsirkin wrote:
> On Wed, Jan 13, 2021 at 04:08:57PM +0800, Xuan Zhuo wrote:
>> The number of queues implemented by many virtio backends is limited,
>> especially some machines have a large number of CPUs. In this case, it
>> is often impossible to allocate a separate queue for XDP_TX.
>>
>> This patch allows XDP_TX to run by reuse the existing SQ with
>> __netif_tx_lock() hold when there are not enough queues.
>>
>> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
>> Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
> I'd like to get some advice on whether this is ok from some
> XDP experts - previously my understanding was that it is
> preferable to disable XDP for such devices than
> use locks on XDP fast path.
I think this is acceptable on the device that changing the number of
queues is not easy. For virtio-net, it probably requires a lot of
changes in the management.
Another example is TUN which use TX lock for XDP.
Thanks
>
>> ---
>> drivers/net/virtio_net.c | 47 +++++++++++++++++++++++++++++++++++------------
>> 1 file changed, 35 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index ba8e637..7a3b2a7 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -195,6 +195,9 @@ struct virtnet_info {
>> /* # of XDP queue pairs currently used by the driver */
>> u16 xdp_queue_pairs;
>>
>> + /* xdp_queue_pairs may be 0, when xdp is already loaded. So add this. */
>> + bool xdp_enabled;
>> +
>> /* I like... big packets and I cannot lie! */
>> bool big_packets;
>>
>> @@ -481,14 +484,34 @@ static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
>> return 0;
>> }
>>
>> -static struct send_queue *virtnet_xdp_sq(struct virtnet_info *vi)
>> +static struct send_queue *virtnet_get_xdp_sq(struct virtnet_info *vi)
>> {
>> unsigned int qp;
>> + struct netdev_queue *txq;
>> +
>> + if (vi->curr_queue_pairs > nr_cpu_ids) {
>> + qp = vi->curr_queue_pairs - vi->xdp_queue_pairs + smp_processor_id();
>> + } else {
>> + qp = smp_processor_id() % vi->curr_queue_pairs;
>> + txq = netdev_get_tx_queue(vi->dev, qp);
>> + __netif_tx_lock(txq, raw_smp_processor_id());
>> + }
>>
>> - qp = vi->curr_queue_pairs - vi->xdp_queue_pairs + smp_processor_id();
>> return &vi->sq[qp];
>> }
>>
>> +static void virtnet_put_xdp_sq(struct virtnet_info *vi)
>> +{
>> + unsigned int qp;
>> + struct netdev_queue *txq;
>> +
>> + if (vi->curr_queue_pairs <= nr_cpu_ids) {
>> + qp = smp_processor_id() % vi->curr_queue_pairs;
>> + txq = netdev_get_tx_queue(vi->dev, qp);
>> + __netif_tx_unlock(txq);
>> + }
>> +}
>> +
>> static int virtnet_xdp_xmit(struct net_device *dev,
>> int n, struct xdp_frame **frames, u32 flags)
>> {
>> @@ -512,7 +535,7 @@ static int virtnet_xdp_xmit(struct net_device *dev,
>> if (!xdp_prog)
>> return -ENXIO;
>>
>> - sq = virtnet_xdp_sq(vi);
>> + sq = virtnet_get_xdp_sq(vi);
>>
>> if (unlikely(flags & ~XDP_XMIT_FLAGS_MASK)) {
>> ret = -EINVAL;
>> @@ -560,12 +583,13 @@ static int virtnet_xdp_xmit(struct net_device *dev,
>> sq->stats.kicks += kicks;
>> u64_stats_update_end(&sq->stats.syncp);
>>
>> + virtnet_put_xdp_sq(vi);
>> return ret;
>> }
>>
>> static unsigned int virtnet_get_headroom(struct virtnet_info *vi)
>> {
>> - return vi->xdp_queue_pairs ? VIRTIO_XDP_HEADROOM : 0;
>> + return vi->xdp_enabled ? VIRTIO_XDP_HEADROOM : 0;
>> }
>>
>> /* We copy the packet for XDP in the following cases:
>> @@ -1457,12 +1481,13 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
>> xdp_do_flush();
>>
>> if (xdp_xmit & VIRTIO_XDP_TX) {
>> - sq = virtnet_xdp_sq(vi);
>> + sq = virtnet_get_xdp_sq(vi);
>> if (virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq)) {
>> u64_stats_update_begin(&sq->stats.syncp);
>> sq->stats.kicks++;
>> u64_stats_update_end(&sq->stats.syncp);
>> }
>> + virtnet_put_xdp_sq(vi);
>> }
>>
>> return received;
>> @@ -2416,12 +2441,8 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
>> xdp_qp = nr_cpu_ids;
>>
>> /* XDP requires extra queues for XDP_TX */
>> - if (curr_qp + xdp_qp > vi->max_queue_pairs) {
>> - NL_SET_ERR_MSG_MOD(extack, "Too few free TX rings available");
>> - netdev_warn(dev, "request %i queues but max is %i\n",
>> - curr_qp + xdp_qp, vi->max_queue_pairs);
>> - return -ENOMEM;
>> - }
>> + if (curr_qp + xdp_qp > vi->max_queue_pairs)
>> + xdp_qp = 0;
>>
>> old_prog = rtnl_dereference(vi->rq[0].xdp_prog);
>> if (!prog && !old_prog)
>> @@ -2453,12 +2474,14 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
>> netif_set_real_num_rx_queues(dev, curr_qp + xdp_qp);
>> vi->xdp_queue_pairs = xdp_qp;
>>
>> + vi->xdp_enabled = false;
>> if (prog) {
>> for (i = 0; i < vi->max_queue_pairs; i++) {
>> rcu_assign_pointer(vi->rq[i].xdp_prog, prog);
>> if (i == 0 && !old_prog)
>> virtnet_clear_guest_offloads(vi);
>> }
>> + vi->xdp_enabled = true;
>> }
>>
>> for (i = 0; i < vi->max_queue_pairs; i++) {
>> @@ -2526,7 +2549,7 @@ static int virtnet_set_features(struct net_device *dev,
>> int err;
>>
>> if ((dev->features ^ features) & NETIF_F_LRO) {
>> - if (vi->xdp_queue_pairs)
>> + if (vi->xdp_enabled)
>> return -EBUSY;
>>
>> if (features & NETIF_F_LRO)
>> --
>> 1.8.3.1
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^ permalink raw reply [flat|nested] 3+ messages in thread