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Message-ID: <cff8d1b7-8267-75a0-cfef-5330a1442742@redhat.com>
Date: Tue, 9 Mar 2021 10:47:26 +0800
From: Jason Wang <jasowang@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: "Michael S. Tsirkin" <mst@...hat.com>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Jesper Dangaard Brouer <hawk@...nel.org>,
John Fastabend <john.fastabend@...il.com>,
virtualization@...ts.linux-foundation.org, bpf@...r.kernel.org,
netdev@...r.kernel.org
Subject: Re: [PATCH v7 net-next] virtio-net: support XDP when not more queues
On 2021/3/9 10:31 上午, Xuan Zhuo wrote:
> On Tue, 9 Mar 2021 10:17:16 +0800, Jason Wang <jasowang@...hat.com> wrote:
>> On 2021/3/8 4:52 下午, 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/XDP_REDIRECT, then xdp cannot be loaded to work, even xdp does
>>> not use the XDP_TX/XDP_REDIRECT.
>>>
>>> This patch allows XDP_TX/XDP_REDIRECT to run by reuse the existing SQ
>>> with __netif_tx_lock() hold when there are not enough queues.
>>>
>>> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
>>> Reviewed-by: Dust Li <dust.li@...ux.alibaba.com>
>>> ---
>>> v7: 1. use macros to implement get/put
>>> 2. remove 'flag'. (suggested by Jason Wang)
>>>
>>> v6: 1. use __netif_tx_acquire()/__netif_tx_release(). (suggested by Jason Wang)
>>> 2. add note for why not lock. (suggested by Jason Wang)
>>> 3. Use variable 'flag' to record with or without locked. It is not safe to
>>> use curr_queue_pairs in "virtnet_put_xdp_sq", because it may changed after
>>> "virtnet_get_xdp_sq".
>>>
>>> v5: change subject from 'support XDP_TX when not more queues'
>>>
>>> v4: make sparse happy
>>> suggested by Jakub Kicinski
>>>
>>> v3: add warning when no more queues
>>> suggested by Jesper Dangaard Brouer
>>>
>>> drivers/net/virtio_net.c | 55 ++++++++++++++++++++++++++++++++++++------------
>>> 1 file changed, 42 insertions(+), 13 deletions(-)
>>>
>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>>> index ba8e637..5ce40ec 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;
>>>
>>> @@ -481,12 +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)
>>> -{
>>> - unsigned int qp;
>>> -
>>> - qp = vi->curr_queue_pairs - vi->xdp_queue_pairs + smp_processor_id();
>>> - return &vi->sq[qp];
>>> +/* when vi->curr_queue_pairs > nr_cpu_ids, the txq/sq is only used for xdp tx on
>>> + * the current cpu, so it does not need to be locked.
>>> + */
>>> +#define virtnet_xdp_get_sq(vi) ({ \
>>> + struct netdev_queue *txq; \
>>> + typeof(vi) v = (vi); \
>>
>> Any reason for not using vi directly?
>>
>> Other looks good.
>>
>> Thanks
> Using vi directly, I got an error by checkpatch.pl:
>
> Macro argument reuse 'vi' - possible side-effects
>
> more info: https://gcc.gnu.org/onlinedocs/cpp/Duplication-of-Side-Effects.html
>
> Thanks.
Ok.
Acked-by: Jason Wang <jasowang@...hat.com>
Thanks
>
>>
>>> + unsigned int qp; \
>>> + if (v->curr_queue_pairs > nr_cpu_ids) { \
>>> + qp = v->curr_queue_pairs - v->xdp_queue_pairs; \
>>> + qp += smp_processor_id(); \
>>> + txq = netdev_get_tx_queue(v->dev, qp); \
>>> + __netif_tx_acquire(txq); \
>>> + } else { \
>>> + qp = smp_processor_id() % v->curr_queue_pairs; \
>>> + txq = netdev_get_tx_queue(v->dev, qp); \
>>> + __netif_tx_lock(txq, raw_smp_processor_id()); \
>>> + } \
>>> + v->sq + qp; \
>>> +})
>>> +
>>> +#define virtnet_xdp_put_sq(vi, q) { \
>>> + struct netdev_queue *txq; \
>>> + typeof(vi) v = (vi); \
>>> + txq = netdev_get_tx_queue(v->dev, (q) - v->sq); \
>>> + if (v->curr_queue_pairs > nr_cpu_ids) \
>>> + __netif_tx_release(txq); \
>>> + else \
>>> + __netif_tx_unlock(txq); \
>>> }
>>>
>>> static int virtnet_xdp_xmit(struct net_device *dev,
>>> @@ -512,7 +537,7 @@ static int virtnet_xdp_xmit(struct net_device *dev,
>>> if (!xdp_prog)
>>> return -ENXIO;
>>>
>>> - sq = virtnet_xdp_sq(vi);
>>> + sq = virtnet_xdp_get_sq(vi);
>>>
>>> if (unlikely(flags & ~XDP_XMIT_FLAGS_MASK)) {
>>> ret = -EINVAL;
>>> @@ -560,12 +585,13 @@ static int virtnet_xdp_xmit(struct net_device *dev,
>>> sq->stats.kicks += kicks;
>>> u64_stats_update_end(&sq->stats.syncp);
>>>
>>> + virtnet_xdp_put_sq(vi, sq);
>>> 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 +1483,13 @@ 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_xdp_get_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_xdp_put_sq(vi, sq);
>>> }
>>>
>>> return received;
>>> @@ -2417,10 +2444,9 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
>>>
>>> /* 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",
>>> + netdev_warn(dev, "XDP request %i queues but max is %i. XDP_TX and XDP_REDIRECT will operate in a slower locked tx mode.\n",
>>> curr_qp + xdp_qp, vi->max_queue_pairs);
>>> - return -ENOMEM;
>>> + xdp_qp = 0;
>>> }
>>>
>>> old_prog = rtnl_dereference(vi->rq[0].xdp_prog);
>>> @@ -2454,11 +2480,14 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
>>> vi->xdp_queue_pairs = xdp_qp;
>>>
>>> if (prog) {
>>> + vi->xdp_enabled = true;
>>> 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);
>>> }
>>> + } else {
>>> + vi->xdp_enabled = false;
>>> }
>>>
>>> for (i = 0; i < vi->max_queue_pairs; i++) {
>>> @@ -2526,7 +2555,7 @@ 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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