1  // SPDX-License-Identifier: GPL-2.0-or-later
2  /*
3   * IPVS:        Never Queue scheduling module
4   *
5   * Authors:     Wensong Zhang <wensong@linuxvirtualserver.org>
6   *
7   * Changes:
8   */
9  
10  /*
11   * The NQ algorithm adopts a two-speed model. When there is an idle server
12   * available, the job will be sent to the idle server, instead of waiting
13   * for a fast one. When there is no idle server available, the job will be
14   * sent to the server that minimize its expected delay (The Shortest
15   * Expected Delay scheduling algorithm).
16   *
17   * See the following paper for more information:
18   * A. Weinrib and S. Shenker, Greed is not enough: Adaptive load sharing
19   * in large heterogeneous systems. In Proceedings IEEE INFOCOM'88,
20   * pages 986-994, 1988.
21   *
22   * Thanks must go to Marko Buuri <marko@buuri.name> for talking NQ to me.
23   *
24   * The difference between NQ and SED is that NQ can improve overall
25   * system utilization.
26   *
27   */
28  
29  #define KMSG_COMPONENT "IPVS"
30  #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
31  
32  #include <linux/module.h>
33  #include <linux/kernel.h>
34  
35  #include <net/ip_vs.h>
36  
37  
38  static inline int
ip_vs_nq_dest_overhead(struct ip_vs_dest * dest)39  ip_vs_nq_dest_overhead(struct ip_vs_dest *dest)
40  {
41  	/*
42  	 * We only use the active connection number in the cost
43  	 * calculation here.
44  	 */
45  	return atomic_read(&dest->activeconns) + 1;
46  }
47  
48  
49  /*
50   *	Weighted Least Connection scheduling
51   */
52  static struct ip_vs_dest *
ip_vs_nq_schedule(struct ip_vs_service * svc,const struct sk_buff * skb,struct ip_vs_iphdr * iph)53  ip_vs_nq_schedule(struct ip_vs_service *svc, const struct sk_buff *skb,
54  		  struct ip_vs_iphdr *iph)
55  {
56  	struct ip_vs_dest *dest, *least = NULL;
57  	int loh = 0, doh;
58  
59  	IP_VS_DBG(6, "%s(): Scheduling...\n", __func__);
60  
61  	/*
62  	 * We calculate the load of each dest server as follows:
63  	 *	(server expected overhead) / dest->weight
64  	 *
65  	 * Remember -- no floats in kernel mode!!!
66  	 * The comparison of h1*w2 > h2*w1 is equivalent to that of
67  	 *		  h1/w1 > h2/w2
68  	 * if every weight is larger than zero.
69  	 *
70  	 * The server with weight=0 is quiesced and will not receive any
71  	 * new connections.
72  	 */
73  
74  	list_for_each_entry_rcu(dest, &svc->destinations, n_list) {
75  
76  		if (dest->flags & IP_VS_DEST_F_OVERLOAD ||
77  		    !atomic_read(&dest->weight))
78  			continue;
79  
80  		doh = ip_vs_nq_dest_overhead(dest);
81  
82  		/* return the server directly if it is idle */
83  		if (atomic_read(&dest->activeconns) == 0) {
84  			least = dest;
85  			loh = doh;
86  			goto out;
87  		}
88  
89  		if (!least ||
90  		    ((__s64)loh * atomic_read(&dest->weight) >
91  		     (__s64)doh * atomic_read(&least->weight))) {
92  			least = dest;
93  			loh = doh;
94  		}
95  	}
96  
97  	if (!least) {
98  		ip_vs_scheduler_err(svc, "no destination available");
99  		return NULL;
100  	}
101  
102    out:
103  	IP_VS_DBG_BUF(6, "NQ: server %s:%u "
104  		      "activeconns %d refcnt %d weight %d overhead %d\n",
105  		      IP_VS_DBG_ADDR(least->af, &least->addr),
106  		      ntohs(least->port),
107  		      atomic_read(&least->activeconns),
108  		      refcount_read(&least->refcnt),
109  		      atomic_read(&least->weight), loh);
110  
111  	return least;
112  }
113  
114  
115  static struct ip_vs_scheduler ip_vs_nq_scheduler =
116  {
117  	.name =			"nq",
118  	.refcnt =		ATOMIC_INIT(0),
119  	.module =		THIS_MODULE,
120  	.n_list =		LIST_HEAD_INIT(ip_vs_nq_scheduler.n_list),
121  	.schedule =		ip_vs_nq_schedule,
122  };
123  
124  
ip_vs_nq_init(void)125  static int __init ip_vs_nq_init(void)
126  {
127  	return register_ip_vs_scheduler(&ip_vs_nq_scheduler);
128  }
129  
ip_vs_nq_cleanup(void)130  static void __exit ip_vs_nq_cleanup(void)
131  {
132  	unregister_ip_vs_scheduler(&ip_vs_nq_scheduler);
133  	synchronize_rcu();
134  }
135  
136  module_init(ip_vs_nq_init);
137  module_exit(ip_vs_nq_cleanup);
138  MODULE_LICENSE("GPL");
139  MODULE_DESCRIPTION("ipvs never queue scheduler");
140