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Message-ID: <CACGkMEv+=k+RvbN2kWp85f9NWPYOPQtqkThdjvOrf5mWonBqvw@mail.gmail.com>
Date: Mon, 4 Mar 2024 14:55:53 +0800
From: Jason Wang <jasowang@...hat.com>
To: Yunjian Wang <wangyunjian@...wei.com>
Cc: mst@...hat.com, willemdebruijn.kernel@...il.com, kuba@...nel.org,
bjorn@...nel.org, magnus.karlsson@...el.com, maciej.fijalkowski@...el.com,
jonathan.lemon@...il.com, davem@...emloft.net, bpf@...r.kernel.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
virtualization@...ts.linux.dev, xudingke@...wei.com, liwei395@...wei.com
Subject: Re: [PATCH net-next v2 3/3] tun: AF_XDP Tx zero-copy support
On Wed, Feb 28, 2024 at 7:06 PM Yunjian Wang <wangyunjian@...wei.com> wrote:
>
> This patch set allows TUN to support the AF_XDP Tx zero-copy feature,
> which can significantly reduce CPU utilization for XDP programs.
>
> Since commit fc72d1d54dd9 ("tuntap: XDP transmission"), the pointer
> ring has been utilized to queue different types of pointers by encoding
> the type into the lower bits. Therefore, we introduce a new flag,
> TUN_XDP_DESC_FLAG(0x2UL), which allows us to enqueue XDP descriptors
> and differentiate them from XDP buffers and sk_buffs. Additionally, a
> spin lock is added for enabling and disabling operations on the xsk pool.
>
> The performance testing was performed on a Intel E5-2620 2.40GHz machine.
> Traffic were generated/send through TUN(testpmd txonly with AF_XDP)
> to VM (testpmd rxonly in guest).
>
> +------+---------+---------+---------+
> | | copy |zero-copy| speedup |
> +------+---------+---------+---------+
> | UDP | Mpps | Mpps | % |
> | 64 | 2.5 | 4.0 | 60% |
> | 512 | 2.1 | 3.6 | 71% |
> | 1024 | 1.9 | 3.3 | 73% |
> +------+---------+---------+---------+
>
> Signed-off-by: Yunjian Wang <wangyunjian@...wei.com>
> ---
> drivers/net/tun.c | 177 +++++++++++++++++++++++++++++++++++++++--
> drivers/vhost/net.c | 4 +
> include/linux/if_tun.h | 32 ++++++++
> 3 files changed, 208 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index bc80fc1d576e..7f4ff50b532c 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -63,6 +63,7 @@
> #include <net/rtnetlink.h>
> #include <net/sock.h>
> #include <net/xdp.h>
> +#include <net/xdp_sock_drv.h>
> #include <net/ip_tunnels.h>
> #include <linux/seq_file.h>
> #include <linux/uio.h>
> @@ -86,6 +87,7 @@ static void tun_default_link_ksettings(struct net_device *dev,
> struct ethtool_link_ksettings *cmd);
>
> #define TUN_RX_PAD (NET_IP_ALIGN + NET_SKB_PAD)
> +#define TUN_XDP_BATCH 64
>
> /* TUN device flags */
>
> @@ -146,6 +148,9 @@ struct tun_file {
> struct tun_struct *detached;
> struct ptr_ring tx_ring;
> struct xdp_rxq_info xdp_rxq;
> + struct xsk_buff_pool *xsk_pool;
> + spinlock_t pool_lock; /* Protects xsk pool enable/disable */
> + u32 nb_descs;
> };
>
> struct tun_page {
> @@ -614,6 +619,8 @@ void tun_ptr_free(void *ptr)
> struct xdp_frame *xdpf = tun_ptr_to_xdp(ptr);
>
> xdp_return_frame(xdpf);
> + } else if (tun_is_xdp_desc_frame(ptr)) {
> + return;
> } else {
> __skb_array_destroy_skb(ptr);
> }
> @@ -631,6 +638,37 @@ static void tun_queue_purge(struct tun_file *tfile)
> skb_queue_purge(&tfile->sk.sk_error_queue);
> }
>
> +static void tun_set_xsk_pool(struct tun_file *tfile, struct xsk_buff_pool *pool)
> +{
> + if (!pool)
> + return;
> +
> + spin_lock(&tfile->pool_lock);
> + xsk_pool_set_rxq_info(pool, &tfile->xdp_rxq);
> + tfile->xsk_pool = pool;
> + spin_unlock(&tfile->pool_lock);
> +}
> +
> +static void tun_clean_xsk_pool(struct tun_file *tfile)
> +{
> + spin_lock(&tfile->pool_lock);
> + if (tfile->xsk_pool) {
> + void *ptr;
> +
> + while ((ptr = ptr_ring_consume(&tfile->tx_ring)) != NULL)
> + tun_ptr_free(ptr);
> +
> + if (tfile->nb_descs) {
> + xsk_tx_completed(tfile->xsk_pool, tfile->nb_descs);
> + if (xsk_uses_need_wakeup(tfile->xsk_pool))
> + xsk_set_tx_need_wakeup(tfile->xsk_pool);
> + tfile->nb_descs = 0;
> + }
> + tfile->xsk_pool = NULL;
> + }
> + spin_unlock(&tfile->pool_lock);
> +}
> +
> static void __tun_detach(struct tun_file *tfile, bool clean)
> {
> struct tun_file *ntfile;
> @@ -648,6 +686,11 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
> u16 index = tfile->queue_index;
> BUG_ON(index >= tun->numqueues);
>
> + ntfile = rtnl_dereference(tun->tfiles[tun->numqueues - 1]);
> + /* Stop xsk zc xmit */
> + tun_clean_xsk_pool(tfile);
> + tun_clean_xsk_pool(ntfile);
> +
> rcu_assign_pointer(tun->tfiles[index],
> tun->tfiles[tun->numqueues - 1]);
> ntfile = rtnl_dereference(tun->tfiles[index]);
> @@ -668,6 +711,7 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
> tun_flow_delete_by_queue(tun, tun->numqueues + 1);
> /* Drop read queue */
> tun_queue_purge(tfile);
> + tun_set_xsk_pool(ntfile, xsk_get_pool_from_qid(tun->dev, index));
> tun_set_real_num_queues(tun);
> } else if (tfile->detached && clean) {
> tun = tun_enable_queue(tfile);
> @@ -801,6 +845,7 @@ static int tun_attach(struct tun_struct *tun, struct file *file,
>
> if (tfile->xdp_rxq.queue_index != tfile->queue_index)
> tfile->xdp_rxq.queue_index = tfile->queue_index;
> + tun_set_xsk_pool(tfile, xsk_get_pool_from_qid(dev, tfile->queue_index));
> } else {
> /* Setup XDP RX-queue info, for new tfile getting attached */
> err = xdp_rxq_info_reg(&tfile->xdp_rxq,
> @@ -1221,11 +1266,50 @@ static int tun_xdp_set(struct net_device *dev, struct bpf_prog *prog,
> return 0;
> }
>
> +static int tun_xsk_pool_enable(struct net_device *netdev,
> + struct xsk_buff_pool *pool,
> + u16 qid)
> +{
> + struct tun_struct *tun = netdev_priv(netdev);
> + struct tun_file *tfile;
> +
> + if (qid >= tun->numqueues)
> + return -EINVAL;
> +
> + tfile = rtnl_dereference(tun->tfiles[qid]);
> + tun_set_xsk_pool(tfile, pool);
> +
> + return 0;
> +}
> +
> +static int tun_xsk_pool_disable(struct net_device *netdev, u16 qid)
> +{
> + struct tun_struct *tun = netdev_priv(netdev);
> + struct tun_file *tfile;
> +
> + if (qid >= MAX_TAP_QUEUES)
> + return -EINVAL;
> +
> + tfile = rtnl_dereference(tun->tfiles[qid]);
> + if (tfile)
> + tun_clean_xsk_pool(tfile);
> + return 0;
> +}
> +
> +static int tun_xsk_pool_setup(struct net_device *dev, struct xsk_buff_pool *pool,
> + u16 qid)
> +{
> + return pool ? tun_xsk_pool_enable(dev, pool, qid) :
> + tun_xsk_pool_disable(dev, qid);
> +}
> +
> static int tun_xdp(struct net_device *dev, struct netdev_bpf *xdp)
> {
> switch (xdp->command) {
> case XDP_SETUP_PROG:
> return tun_xdp_set(dev, xdp->prog, xdp->extack);
> + case XDP_SETUP_XSK_POOL:
> + return tun_xsk_pool_setup(dev, xdp->xsk.pool, xdp->xsk.queue_id);
> default:
> return -EINVAL;
> }
> @@ -1330,6 +1414,19 @@ static int tun_xdp_tx(struct net_device *dev, struct xdp_buff *xdp)
> return nxmit;
> }
>
> +static int tun_xsk_wakeup(struct net_device *dev, u32 qid, u32 flags)
> +{
> + struct tun_struct *tun = netdev_priv(dev);
> + struct tun_file *tfile;
> +
> + rcu_read_lock();
> + tfile = rcu_dereference(tun->tfiles[qid]);
> + if (tfile)
> + __tun_xdp_flush_tfile(tfile);
> + rcu_read_unlock();
> + return 0;
> +}
I may miss something but why not simply queue xdp frames into ptr ring
then we don't need tricks for peek?
Thanks
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