Re: [PATCH net-next v4 08/10] virtio-net: xsk zero copy xmit setup

[Jason Wang <jasowang@redhat.com>]

在 2021/4/14 下午3:36, Magnus Karlsson 写道:
> On Tue, Apr 13, 2021 at 9:58 AM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
>> xsk is a high-performance packet receiving and sending technology.
>>
>> This patch implements the binding and unbinding operations of xsk and
>> the virtio-net queue for xsk zero copy xmit.
>>
>> The xsk zero copy xmit depends on tx napi. So if tx napi is not true,
>> an error will be reported. And the entire operation is under the
>> protection of rtnl_lock.
>>
>> If xsk is active, it will prevent ethtool from modifying tx napi.
>>
>> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
>> Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
>> ---
>>   drivers/net/virtio_net.c | 78 +++++++++++++++++++++++++++++++++++++++-
>>   1 file changed, 77 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index f52a25091322..8242a9e9f17d 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -22,6 +22,7 @@
>>   #include <net/route.h>
>>   #include <net/xdp.h>
>>   #include <net/net_failover.h>
>> +#include <net/xdp_sock_drv.h>
>>
>>   static int napi_weight = NAPI_POLL_WEIGHT;
>>   module_param(napi_weight, int, 0444);
>> @@ -133,6 +134,11 @@ struct send_queue {
>>          struct virtnet_sq_stats stats;
>>
>>          struct napi_struct napi;
>> +
>> +       struct {
>> +               /* xsk pool */
>> +               struct xsk_buff_pool __rcu *pool;
>> +       } xsk;
>>   };
>>
>>   /* Internal representation of a receive virtqueue */
>> @@ -2249,8 +2255,19 @@ static int virtnet_set_coalesce(struct net_device *dev,
>>          if (napi_weight ^ vi->sq[0].napi.weight) {
>>                  if (dev->flags & IFF_UP)
>>                          return -EBUSY;
>> -               for (i = 0; i < vi->max_queue_pairs; i++)
>> +               for (i = 0; i < vi->max_queue_pairs; i++) {
>> +                       /* xsk xmit depend on the tx napi. So if xsk is active,
>> +                        * prevent modifications to tx napi.
>> +                        */
>> +                       rcu_read_lock();
>> +                       if (rcu_dereference(vi->sq[i].xsk.pool)) {
>> +                               rcu_read_unlock();
>> +                               continue;
>> +                       }
>> +                       rcu_read_unlock();
>> +
>>                          vi->sq[i].napi.weight = napi_weight;
>> +               }
>>          }
>>
>>          return 0;
>> @@ -2518,11 +2535,70 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
>>          return err;
>>   }
>>
>> +static int virtnet_xsk_pool_enable(struct net_device *dev,
>> +                                  struct xsk_buff_pool *pool,
>> +                                  u16 qid)
>> +{
>> +       struct virtnet_info *vi = netdev_priv(dev);
>> +       struct send_queue *sq;
>> +
>> +       if (qid >= vi->curr_queue_pairs)
>> +               return -EINVAL;
> Your implementation is the first implementation that only supports
> zerocopy for one out of Rx and Tx, and this will currently confuse the
> control plane in some situations since it assumes that both Rx and Tx
> are enabled by a call to this NDO. For example: user space creates an
> xsk socket with both an Rx and a Tx ring, then calls bind with the
> XDP_ZEROCOPY flag. In this case, the call should fail if the device is
> virtio-net since it only supports zerocopy for Tx. But it should
> succeed if the user only created a Tx ring since that makes it a
> Tx-only socket which can be supported.
>
> So you need to introduce a new interface in xdp_sock_drv.h that can be
> used to ask if this socket has Rx enabled and if so fail the call (at
> least one of them has to be enabled, otherwise the bind call would
> fail before this ndo is called). Then the logic above will act on that
> and try to fall back to copy mode (if allowed). Such an interface
> (with an added "is_tx_enabled") might in the future be useful for
> physical NIC drivers too if they would like to save on resources for
> Tx-only and Rx-only sockets. Currently, they all just assume every
> socket is Rx and Tx.


So if there's no blocker for implementing the zerocopy RX, I think we'd 
better to implement it in this series without introducing new APIs for 
the upper layer.

Thanks


>
> Thanks: Magnus
>
>> +
>> +       sq = &vi->sq[qid];
>> +
>> +       /* xsk zerocopy depend on the tx napi.
>> +        *
>> +        * xsk zerocopy xmit is driven by the tx interrupt. When the device is
>> +        * not busy, napi will be called continuously to send data. When the
>> +        * device is busy, wait for the notification interrupt after the
>> +        * hardware has finished processing the data, and continue to send data
>> +        * in napi.
>> +        */
>> +       if (!sq->napi.weight)
>> +               return -EPERM;
>> +
>> +       rcu_read_lock();
>> +       /* Here is already protected by rtnl_lock, so rcu_assign_pointer is
>> +        * safe.
>> +        */
>> +       rcu_assign_pointer(sq->xsk.pool, pool);
>> +       rcu_read_unlock();
>> +
>> +       return 0;
>> +}
>> +
>> +static int virtnet_xsk_pool_disable(struct net_device *dev, u16 qid)
>> +{
>> +       struct virtnet_info *vi = netdev_priv(dev);
>> +       struct send_queue *sq;
>> +
>> +       if (qid >= vi->curr_queue_pairs)
>> +               return -EINVAL;
>> +
>> +       sq = &vi->sq[qid];
>> +
>> +       /* Here is already protected by rtnl_lock, so rcu_assign_pointer is
>> +        * safe.
>> +        */
>> +       rcu_assign_pointer(sq->xsk.pool, NULL);
>> +
>> +       synchronize_net(); /* Sync with the XSK wakeup and with NAPI. */
>> +
>> +       return 0;
>> +}
>> +
>>   static int virtnet_xdp(struct net_device *dev, struct netdev_bpf *xdp)
>>   {
>>          switch (xdp->command) {
>>          case XDP_SETUP_PROG:
>>                  return virtnet_xdp_set(dev, xdp->prog, xdp->extack);
>> +       case XDP_SETUP_XSK_POOL:
>> +               if (xdp->xsk.pool)
>> +                       return virtnet_xsk_pool_enable(dev, xdp->xsk.pool,
>> +                                                      xdp->xsk.queue_id);
>> +               else
>> +                       return virtnet_xsk_pool_disable(dev, xdp->xsk.queue_id);
>>          default:
>>                  return -EINVAL;
>>          }
>> --
>> 2.31.0
>>