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Date: Thu, 26 Oct 2023 11:41:54 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Coco Li <lixiaoyan@...gle.com>
Cc: Jakub Kicinski <kuba@...nel.org>, Neal Cardwell <ncardwell@...gle.com>,
Mubashir Adnan Qureshi <mubashirq@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Andrew Lunn <andrew@...n.ch>,
Jonathan Corbet <corbet@....net>, David Ahern <dsahern@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org, Chao Wu <wwchao@...gle.com>,
Wei Wang <weiwan@...gle.com>, Pradeep Nemavat <pnemavat@...gle.com>
Subject: Re: [PATCH v4 net-next 5/6] net-device: reorganize net_device fast
path variables
On Thu, Oct 26, 2023 at 10:20 AM Coco Li <lixiaoyan@...gle.com> wrote:
>
> Reorganize fast path variables on tx-txrx-rx order
> Fastpath variables end after npinfo.
>
> Below data generated with pahole on x86 architecture.
>
> Fast path variables span cache lines before change: 12
> Fast path variables span cache lines after change: 4
>
> Signed-off-by: Coco Li <lixiaoyan@...gle.com>
> Suggested-by: Eric Dumazet <edumazet@...gle.com>
> Reviewed-by: David Ahern <dsahern@...nel.org>
> ---
> include/linux/netdevice.h | 113 ++++++++++++++++++++------------------
> net/core/dev.c | 51 +++++++++++++++++
> 2 files changed, 111 insertions(+), 53 deletions(-)
>
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index b8bf669212cce..26c4d57451bf0 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -2076,6 +2076,66 @@ enum netdev_ml_priv_type {
> */
>
> struct net_device {
> + /* Cacheline organization can be found documented in
> + * Documentation/networking/net_cachelines/net_device.rst.
> + * Please update the document when adding new fields.
> + */
> +
> + /* TX read-mostly hotpath */
> + __cacheline_group_begin(net_device_read);
This should be net_device_write ? Or perhaps simply tx ?
> + unsigned long long priv_flags;
> + const struct net_device_ops *netdev_ops;
> + const struct header_ops *header_ops;
> + struct netdev_queue *_tx;
> + unsigned int real_num_tx_queues;
> + unsigned int gso_max_size;
> + unsigned int gso_ipv4_max_size;
> + u16 gso_max_segs;
> + s16 num_tc;
> + /* Note : dev->mtu is often read without holding a lock.
> + * Writers usually hold RTNL.
> + * It is recommended to use READ_ONCE() to annotate the reads,
> + * and to use WRITE_ONCE() to annotate the writes.
> + */
> + unsigned int mtu;
> + unsigned short needed_headroom;
> + struct netdev_tc_txq tc_to_txq[TC_MAX_QUEUE];
> +#ifdef CONFIG_XPS
> + struct xps_dev_maps __rcu *xps_maps[XPS_MAPS_MAX];
> +#endif
> +#ifdef CONFIG_NETFILTER_EGRESS
> + struct nf_hook_entries __rcu *nf_hooks_egress;
> +#endif
> +#ifdef CONFIG_NET_XGRESS
> + struct bpf_mprog_entry __rcu *tcx_egress;
> +#endif
> +
__cacheline_group_end(tx);
__cacheline_group_begin(txrx);
> + /* TXRX read-mostly hotpath */
> + unsigned int flags;
> + unsigned short hard_header_len;
> + netdev_features_t features;
> + struct inet6_dev __rcu *ip6_ptr;
> +
__cacheline_group_end(txrx);
__cacheline_group_begin(rx);
> + /* RX read-mostly hotpath */
> + struct list_head ptype_specific;
> + int ifindex;
> + unsigned int real_num_rx_queues;
> + struct netdev_rx_queue *_rx;
> + unsigned long gro_flush_timeout;
> + int napi_defer_hard_irqs;
> + unsigned int gro_max_size;
> + unsigned int gro_ipv4_max_size;
> + rx_handler_func_t __rcu *rx_handler;
> + void __rcu *rx_handler_data;
> + possible_net_t nd_net;
> +#ifdef CONFIG_NETPOLL
> + struct netpoll_info __rcu *npinfo;
> +#endif
> +#ifdef CONFIG_NET_XGRESS
> + struct bpf_mprog_entry __rcu *tcx_ingress;
> +#endif
> + __cacheline_group_end(net_device_read);
> +
> char name[IFNAMSIZ];
> struct netdev_name_node *name_node;
> struct dev_ifalias __rcu *ifalias;
> @@ -2100,7 +2160,6 @@ struct net_device {
> struct list_head unreg_list;
> struct list_head close_list;
> struct list_head ptype_all;
> - struct list_head ptype_specific;
>
> struct {
> struct list_head upper;
> @@ -2108,25 +2167,12 @@ struct net_device {
> } adj_list;
>
> /* Read-mostly cache-line for fast-path access */
> - unsigned int flags;
> xdp_features_t xdp_features;
> - unsigned long long priv_flags;
> - const struct net_device_ops *netdev_ops;
> const struct xdp_metadata_ops *xdp_metadata_ops;
> - int ifindex;
> unsigned short gflags;
> - unsigned short hard_header_len;
>
> - /* Note : dev->mtu is often read without holding a lock.
> - * Writers usually hold RTNL.
> - * It is recommended to use READ_ONCE() to annotate the reads,
> - * and to use WRITE_ONCE() to annotate the writes.
> - */
> - unsigned int mtu;
> - unsigned short needed_headroom;
> unsigned short needed_tailroom;
>
> - netdev_features_t features;
> netdev_features_t hw_features;
> netdev_features_t wanted_features;
> netdev_features_t vlan_features;
> @@ -2170,8 +2216,6 @@ struct net_device {
> const struct tlsdev_ops *tlsdev_ops;
> #endif
>
> - const struct header_ops *header_ops;
> -
> unsigned char operstate;
> unsigned char link_mode;
>
> @@ -2212,9 +2256,7 @@ struct net_device {
>
>
> /* Protocol-specific pointers */
> -
> struct in_device __rcu *ip_ptr;
> - struct inet6_dev __rcu *ip6_ptr;
> #if IS_ENABLED(CONFIG_VLAN_8021Q)
> struct vlan_info __rcu *vlan_info;
> #endif
> @@ -2249,26 +2291,14 @@ struct net_device {
> /* Interface address info used in eth_type_trans() */
> const unsigned char *dev_addr;
>
> - struct netdev_rx_queue *_rx;
> unsigned int num_rx_queues;
> - unsigned int real_num_rx_queues;
> -
> struct bpf_prog __rcu *xdp_prog;
> - unsigned long gro_flush_timeout;
> - int napi_defer_hard_irqs;
> #define GRO_LEGACY_MAX_SIZE 65536u
> /* TCP minimal MSS is 8 (TCP_MIN_GSO_SIZE),
> * and shinfo->gso_segs is a 16bit field.
> */
> #define GRO_MAX_SIZE (8 * 65535u)
> - unsigned int gro_max_size;
> - unsigned int gro_ipv4_max_size;
> unsigned int xdp_zc_max_segs;
> - rx_handler_func_t __rcu *rx_handler;
> - void __rcu *rx_handler_data;
> -#ifdef CONFIG_NET_XGRESS
> - struct bpf_mprog_entry __rcu *tcx_ingress;
> -#endif
> struct netdev_queue __rcu *ingress_queue;
> #ifdef CONFIG_NETFILTER_INGRESS
> struct nf_hook_entries __rcu *nf_hooks_ingress;
> @@ -2283,25 +2313,13 @@ struct net_device {
> /*
> * Cache lines mostly used on transmit path
> */
> - struct netdev_queue *_tx ____cacheline_aligned_in_smp;
> unsigned int num_tx_queues;
> - unsigned int real_num_tx_queues;
> struct Qdisc __rcu *qdisc;
> unsigned int tx_queue_len;
> spinlock_t tx_global_lock;
>
> struct xdp_dev_bulk_queue __percpu *xdp_bulkq;
>
> -#ifdef CONFIG_XPS
> - struct xps_dev_maps __rcu *xps_maps[XPS_MAPS_MAX];
> -#endif
> -#ifdef CONFIG_NET_XGRESS
> - struct bpf_mprog_entry __rcu *tcx_egress;
> -#endif
> -#ifdef CONFIG_NETFILTER_EGRESS
> - struct nf_hook_entries __rcu *nf_hooks_egress;
> -#endif
> -
> #ifdef CONFIG_NET_SCHED
> DECLARE_HASHTABLE (qdisc_hash, 4);
> #endif
> @@ -2340,12 +2358,6 @@ struct net_device {
> bool needs_free_netdev;
> void (*priv_destructor)(struct net_device *dev);
>
> -#ifdef CONFIG_NETPOLL
> - struct netpoll_info __rcu *npinfo;
> -#endif
> -
> - possible_net_t nd_net;
> -
> /* mid-layer private */
> void *ml_priv;
> enum netdev_ml_priv_type ml_priv_type;
> @@ -2379,20 +2391,15 @@ struct net_device {
> */
> #define GSO_MAX_SIZE (8 * GSO_MAX_SEGS)
>
> - unsigned int gso_max_size;
> #define TSO_LEGACY_MAX_SIZE 65536
> #define TSO_MAX_SIZE UINT_MAX
> unsigned int tso_max_size;
> - u16 gso_max_segs;
> #define TSO_MAX_SEGS U16_MAX
> u16 tso_max_segs;
> - unsigned int gso_ipv4_max_size;
>
> #ifdef CONFIG_DCB
> const struct dcbnl_rtnl_ops *dcbnl_ops;
> #endif
> - s16 num_tc;
> - struct netdev_tc_txq tc_to_txq[TC_MAX_QUEUE];
> u8 prio_tc_map[TC_BITMASK + 1];
>
> #if IS_ENABLED(CONFIG_FCOE)
> diff --git a/net/core/dev.c b/net/core/dev.c
> index a37a932a3e145..ca7e653e6c348 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -11511,6 +11511,55 @@ static struct pernet_operations __net_initdata default_device_ops = {
> .exit_batch = default_device_exit_batch,
> };
>
> +static void __init net_dev_struct_check(void)
> +{
> + /* TX read-mostly hotpath */
Of course, change net_device_read to either rx, txrx, or tx, depending
of each field purpose/location.
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, priv_flags);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, netdev_ops);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, header_ops);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, _tx);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, real_num_tx_queues);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, gso_max_size);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, gso_ipv4_max_size);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, gso_max_segs);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, num_tc);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, mtu);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, needed_headroom);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, tc_to_txq);
> +#ifdef CONFIG_XPS
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, xps_maps);
> +#endif
> +#ifdef CONFIG_NETFILTER_EGRESS
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, nf_hooks_egress);
> +#endif
> +#ifdef CONFIG_NET_XGRESS
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, tcx_egress);
> +#endif
> + /* TXRX read-mostly hotpath */
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, flags);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, hard_header_len);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, features);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, ip6_ptr);
> + /* RX read-mostly hotpath */
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, ptype_specific);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, ifindex);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, real_num_rx_queues);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, _rx);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, gro_flush_timeout);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, napi_defer_hard_irqs);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, gro_max_size);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, gro_ipv4_max_size);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, rx_handler);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, rx_handler_data);
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, nd_net);
> +#ifdef CONFIG_NETPOLL
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, npinfo);
> +#endif
> +#ifdef CONFIG_NET_XGRESS
> + CACHELINE_ASSERT_GROUP_MEMBER(struct net_device, net_device_read, tcx_ingress);
> +#endif
> +}
> +
> /*
> * Initialize the DEV module. At boot time this walks the device list and
> * unhooks any devices that fail to initialise (normally hardware not
> @@ -11528,6 +11577,8 @@ static int __init net_dev_init(void)
>
> BUG_ON(!dev_boot_phase);
>
> + net_dev_struct_check();
> +
> if (dev_proc_init())
> goto out;
>
> --
> 2.42.0.758.gaed0368e0e-goog
>
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