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Message-ID: <CACGkMEud8Q7fOn85GHGB0D7vcaTQihMYYhSaL=uGh=g1WHZ=HA@mail.gmail.com>
Date: Wed, 6 Mar 2024 10:11:59 +0800
From: Jason Wang <jasowang@...hat.com>
To: wangyunjian <wangyunjian@...wei.com>
Cc: "mst@...hat.com" <mst@...hat.com>,
"willemdebruijn.kernel@...il.com" <willemdebruijn.kernel@...il.com>, "kuba@...nel.org" <kuba@...nel.org>,
"bjorn@...nel.org" <bjorn@...nel.org>, "magnus.karlsson@...el.com" <magnus.karlsson@...el.com>,
"maciej.fijalkowski@...el.com" <maciej.fijalkowski@...el.com>,
"jonathan.lemon@...il.com" <jonathan.lemon@...il.com>, "davem@...emloft.net" <davem@...emloft.net>,
"bpf@...r.kernel.org" <bpf@...r.kernel.org>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
"virtualization@...ts.linux.dev" <virtualization@...ts.linux.dev>, xudingke <xudingke@...wei.com>,
"liwei (DT)" <liwei395@...wei.com>
Subject: Re: [PATCH net-next v2 3/3] tun: AF_XDP Tx zero-copy support
On Mon, Mar 4, 2024 at 7:24 PM wangyunjian <wangyunjian@...wei.com> wrote:
>
>
>
> > -----Original Message-----
> > From: Jason Wang [mailto:jasowang@...hat.com]
> > Sent: Monday, March 4, 2024 2:56 PM
> > To: wangyunjian <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 <xudingke@...wei.com>; liwei (DT)
> > <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?
>
> The current implementation is implemented with reference to other NIC's drivers
> (ixgbe, ice, dpaa2, mlx5), which use XDP descriptors directly.
Well, they all do the same thing which is translate XDP descriptors to
the vendor specific descriptor format.
For TUN, the ptr_ring is the "vendor specific" format.
> Converting XDP
> descriptors to XDP frames does not seem to be very beneficial.
Get rid of the trick for peek like what is done in this patch?
Thanks
>
> Thanks
> >
> > Thanks
>
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