include/net/rps.h

/* SPDX-License-Identifier: GPL-2.0-or-later */
#ifndef _NET_RPS_H
#define _NET_RPS_H

#include <linux/types.h>
#include <linux/static_key.h>
#include <net/sock.h>
#include <net/hotdata.h>

#ifdef CONFIG_RPS

extern struct static_key_false rps_needed;
extern struct static_key_false rfs_needed;

/*
 * This structure holds an RPS map which can be of variable length.  The
 * map is an array of CPUs.
 */
struct rps_map {
	unsigned int	len;
	struct rcu_head	rcu;
	u16		cpus[];
};
#define RPS_MAP_SIZE(_num) (sizeof(struct rps_map) + ((_num) * sizeof(u16)))

/*
 * The rps_dev_flow structure contains the mapping of a flow to a CPU, the
 * tail pointer for that CPU's input queue at the time of last enqueue, and
 * a hardware filter index.
 */
struct rps_dev_flow {
	u16		cpu;
	u16		filter;
	unsigned int	last_qtail;
};
#define RPS_NO_FILTER 0xffff

/*
 * The rps_dev_flow_table structure contains a table of flow mappings.
 */
struct rps_dev_flow_table {
	unsigned int		mask;
	struct rcu_head		rcu;
	struct rps_dev_flow	flows[];
};
#define RPS_DEV_FLOW_TABLE_SIZE(_num) (sizeof(struct rps_dev_flow_table) + \
    ((_num) * sizeof(struct rps_dev_flow)))

/*
 * The rps_sock_flow_table contains mappings of flows to the last CPU
 * on which they were processed by the application (set in recvmsg).
 * Each entry is a 32bit value. Upper part is the high-order bits
 * of flow hash, lower part is CPU number.
 * rps_cpu_mask is used to partition the space, depending on number of
 * possible CPUs : rps_cpu_mask = roundup_pow_of_two(nr_cpu_ids) - 1
 * For example, if 64 CPUs are possible, rps_cpu_mask = 0x3f,
 * meaning we use 32-6=26 bits for the hash.
 */
struct rps_sock_flow_table {
	u32	mask;

	u32	ents[] ____cacheline_aligned_in_smp;
};
#define	RPS_SOCK_FLOW_TABLE_SIZE(_num) (offsetof(struct rps_sock_flow_table, ents[_num]))

#define RPS_NO_CPU 0xffff

static inline void rps_record_sock_flow(struct rps_sock_flow_table *table,
					u32 hash)
{
	unsigned int index = hash & table->mask;
	u32 val = hash & ~net_hotdata.rps_cpu_mask;

	/* We only give a hint, preemption can change CPU under us */
	val |= raw_smp_processor_id();

	/* The following WRITE_ONCE() is paired with the READ_ONCE()
	 * here, and another one in get_rps_cpu().
	 */
	if (READ_ONCE(table->ents[index]) != val)
		WRITE_ONCE(table->ents[index], val);
}

#endif /* CONFIG_RPS */

static inline void sock_rps_record_flow_hash(__u32 hash)
{
#ifdef CONFIG_RPS
	struct rps_sock_flow_table *sock_flow_table;

	if (!hash)
		return;
	rcu_read_lock();
	sock_flow_table = rcu_dereference(net_hotdata.rps_sock_flow_table);
	if (sock_flow_table)
		rps_record_sock_flow(sock_flow_table, hash);
	rcu_read_unlock();
#endif
}

static inline void sock_rps_record_flow(const struct sock *sk)
{
#ifdef CONFIG_RPS
	if (static_branch_unlikely(&rfs_needed)) {
		/* Reading sk->sk_rxhash might incur an expensive cache line
		 * miss.
		 *
		 * TCP_ESTABLISHED does cover almost all states where RFS
		 * might be useful, and is cheaper [1] than testing :
		 *	IPv4: inet_sk(sk)->inet_daddr
		 * 	IPv6: ipv6_addr_any(&sk->sk_v6_daddr)
		 * OR	an additional socket flag
		 * [1] : sk_state and sk_prot are in the same cache line.
		 */
		if (sk->sk_state == TCP_ESTABLISHED) {
			/* This READ_ONCE() is paired with the WRITE_ONCE()
			 * from sock_rps_save_rxhash() and sock_rps_reset_rxhash().
			 */
			sock_rps_record_flow_hash(READ_ONCE(sk->sk_rxhash));
		}
	}
#endif
}

#endif /* _NET_RPS_H */