Re: [net-next PATCH v2 2/4] net: Enable Tx queue selection based on Rx queues

[Tom Herbert <tom@herbertland.com>]

On Tue, May 15, 2018 at 6:26 PM, Amritha Nambiar
<amritha.nambiar@intel.com> wrote:
> This patch adds support to pick Tx queue based on the Rx queue map
> configuration set by the admin through the sysfs attribute
> for each Tx queue. If the user configuration for receive
> queue map does not apply, then the Tx queue selection falls back
> to CPU map based selection and finally to hashing.
>
> Signed-off-by: Amritha Nambiar <amritha.nambiar@intel.com>
> Signed-off-by: Sridhar Samudrala <sridhar.samudrala@intel.com>
> ---
>  include/net/sock.h       |   18 ++++++++++++++++++
>  net/core/dev.c           |   36 +++++++++++++++++++++++++++++-------
>  net/core/sock.c          |    5 +++++
>  net/ipv4/tcp_input.c     |    7 +++++++
>  net/ipv4/tcp_ipv4.c      |    1 +
>  net/ipv4/tcp_minisocks.c |    1 +
>  6 files changed, 61 insertions(+), 7 deletions(-)
>
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 4f7c584..0613f63 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -139,6 +139,8 @@ typedef __u64 __bitwise __addrpair;
>   *     @skc_node: main hash linkage for various protocol lookup tables
>   *     @skc_nulls_node: main hash linkage for TCP/UDP/UDP-Lite protocol
>   *     @skc_tx_queue_mapping: tx queue number for this connection
> + *     @skc_rx_queue_mapping: rx queue number for this connection
> + *     @skc_rx_ifindex: rx ifindex for this connection
>   *     @skc_flags: place holder for sk_flags
>   *             %SO_LINGER (l_onoff), %SO_BROADCAST, %SO_KEEPALIVE,
>   *             %SO_OOBINLINE settings, %SO_TIMESTAMPING settings
> @@ -215,6 +217,10 @@ struct sock_common {
>                 struct hlist_nulls_node skc_nulls_node;
>         };
>         int                     skc_tx_queue_mapping;
> +#ifdef CONFIG_XPS
> +       int                     skc_rx_queue_mapping;
> +       int                     skc_rx_ifindex;

Isn't this increasing size of sock_common for a narrow use case functionality?

> +#endif
>         union {
>                 int             skc_incoming_cpu;
>                 u32             skc_rcv_wnd;
> @@ -326,6 +332,10 @@ struct sock {
>  #define sk_nulls_node          __sk_common.skc_nulls_node
>  #define sk_refcnt              __sk_common.skc_refcnt
>  #define sk_tx_queue_mapping    __sk_common.skc_tx_queue_mapping
> +#ifdef CONFIG_XPS
> +#define sk_rx_queue_mapping    __sk_common.skc_rx_queue_mapping
> +#define sk_rx_ifindex          __sk_common.skc_rx_ifindex
> +#endif
>
>  #define sk_dontcopy_begin      __sk_common.skc_dontcopy_begin
>  #define sk_dontcopy_end                __sk_common.skc_dontcopy_end
> @@ -1696,6 +1706,14 @@ static inline int sk_tx_queue_get(const struct sock *sk)
>         return sk ? sk->sk_tx_queue_mapping : -1;
>  }
>
> +static inline void sk_mark_rx_queue(struct sock *sk, struct sk_buff *skb)
> +{
> +#ifdef CONFIG_XPS
> +       sk->sk_rx_ifindex = skb->skb_iif;
> +       sk->sk_rx_queue_mapping = skb_get_rx_queue(skb);
> +#endif
> +}
> +
>  static inline void sk_set_socket(struct sock *sk, struct socket *sock)
>  {
>         sk_tx_queue_clear(sk);
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 7e5dfdb..4030368 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -3458,18 +3458,14 @@ sch_handle_egress(struct sk_buff *skb, int *ret, struct net_device *dev)
>  }
>  #endif /* CONFIG_NET_EGRESS */
>
> -static inline int get_xps_queue(struct net_device *dev, struct sk_buff *skb)
> -{
>  #ifdef CONFIG_XPS
> -       struct xps_dev_maps *dev_maps;
> +static int __get_xps_queue_idx(struct net_device *dev, struct sk_buff *skb,
> +                              struct xps_dev_maps *dev_maps, unsigned int tci)
> +{
>         struct xps_map *map;
>         int queue_index = -1;
>
> -       rcu_read_lock();
> -       dev_maps = rcu_dereference(dev->xps_maps[XPS_MAP_CPUS]);
>         if (dev_maps) {
> -               unsigned int tci = skb->sender_cpu - 1;
> -
>                 if (dev->num_tc) {
>                         tci *= dev->num_tc;
>                         tci += netdev_get_prio_tc_map(dev, skb->priority);
> @@ -3486,6 +3482,32 @@ static inline int get_xps_queue(struct net_device *dev, struct sk_buff *skb)
>                                 queue_index = -1;
>                 }
>         }
> +       return queue_index;
> +}
> +#endif
> +
> +static int get_xps_queue(struct net_device *dev, struct sk_buff *skb)
> +{
> +#ifdef CONFIG_XPS
> +       enum xps_map_type i = XPS_MAP_RXQS;
> +       struct xps_dev_maps *dev_maps;
> +       struct sock *sk = skb->sk;
> +       int queue_index = -1;
> +       unsigned int tci = 0;
> +
> +       if (sk && sk->sk_rx_queue_mapping <= dev->real_num_rx_queues &&
> +           dev->ifindex == sk->sk_rx_ifindex)
> +               tci = sk->sk_rx_queue_mapping;
> +
> +       rcu_read_lock();
> +       while (queue_index < 0 && i < __XPS_MAP_MAX) {
> +               if (i == XPS_MAP_CPUS)

This while loop typifies exactly why I don't think the XPS maps should
be an array. There's only two and we really don't want this to be an
open ended invitation for people to create new mapping methods. The
code is much simpler and potentially more efficient if the two maps
are just separate pointers. It should look something like this:

dev_maps = rcu_dereference(dev->xps_rxqs_map);
if (dev_maps) {
        queue_index = __get_xps_queue_idx(dev, skb, dev_maps, tci);
        if (queue_index < 0) {
              dev_maps = rcu_dereference(dev->xps_rxqs_map);
              if (dev_maps) {
                     queue_index = __get_xps_queue_idx(dev, skb,
dev_rxqs_maps, tci);
               ...

Also, the rxqs is a pretty narrow use case and it's likely to be
rarely configured (relative to a CPU map). A static_key could be used
to eliminate the cost of the extra map check (the static_key could
also be used on for CPU maps, this is analogous to how there are
static keys for RPS and RFS).

> +                       tci = skb->sender_cpu - 1;
> +               dev_maps = rcu_dereference(dev->xps_maps[i]);
> +               queue_index = __get_xps_queue_idx(dev, skb, dev_maps, tci);
> +               i++;
> +       }
> +
>         rcu_read_unlock();
>
>         return queue_index;
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 042cfc6..73d7fa8 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -2824,6 +2824,11 @@ void sock_init_data(struct socket *sock, struct sock *sk)
>         sk->sk_pacing_rate = ~0U;
>         sk->sk_pacing_shift = 10;
>         sk->sk_incoming_cpu = -1;
> +
> +#ifdef CONFIG_XPS
> +       sk->sk_rx_ifindex = -1;
> +       sk->sk_rx_queue_mapping = -1;
> +#endif
>         /*
>          * Before updating sk_refcnt, we must commit prior changes to memory
>          * (Documentation/RCU/rculist_nulls.txt for details)
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index b188e0d..d33911c 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -78,6 +78,7 @@
>  #include <linux/errqueue.h>
>  #include <trace/events/tcp.h>
>  #include <linux/static_key.h>
> +#include <net/busy_poll.h>
>
>  int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
>
> @@ -5559,6 +5560,11 @@ void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
>                 __tcp_fast_path_on(tp, tp->snd_wnd);
>         else
>                 tp->pred_flags = 0;
> +
> +       if (skb) {
> +               sk_mark_napi_id(sk, skb);
> +               sk_mark_rx_queue(sk, skb);
> +       }
>  }
>
>  static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
> @@ -6371,6 +6377,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
>         tcp_rsk(req)->snt_isn = isn;
>         tcp_rsk(req)->txhash = net_tx_rndhash();
>         tcp_openreq_init_rwin(req, sk, dst);
> +       sk_mark_rx_queue(req_to_sk(req), skb);
>         if (!want_cookie) {
>                 tcp_reqsk_record_syn(sk, req, skb);
>                 fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc, dst);
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index caf23de..abdf02e 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -1479,6 +1479,7 @@ int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb)
>
>                 sock_rps_save_rxhash(sk, skb);
>                 sk_mark_napi_id(sk, skb);
> +               sk_mark_rx_queue(sk, skb);

Can this be done in sock_rps_save_rxhash?

>                 if (dst) {
>                         if (inet_sk(sk)->rx_dst_ifindex != skb->skb_iif ||
>                             !dst->ops->check(dst, 0)) {
> diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
> index f867658..4939c28 100644
> --- a/net/ipv4/tcp_minisocks.c
> +++ b/net/ipv4/tcp_minisocks.c
> @@ -836,6 +836,7 @@ int tcp_child_process(struct sock *parent, struct sock *child,
>
>         /* record NAPI ID of child */
>         sk_mark_napi_id(child, skb);
> +       sk_mark_rx_queue(child, skb);
>
>         tcp_segs_in(tcp_sk(child), skb);
>         if (!sock_owned_by_user(child)) {
>