1 | /* $NetBSD: subr_pserialize.c,v 1.8 2015/06/12 19:18:30 dholland Exp $ */ |
2 | |
3 | /*- |
4 | * Copyright (c) 2010, 2011 The NetBSD Foundation, Inc. |
5 | * All rights reserved. |
6 | * |
7 | * Redistribution and use in source and binary forms, with or without |
8 | * modification, are permitted provided that the following conditions |
9 | * are met: |
10 | * 1. Redistributions of source code must retain the above copyright |
11 | * notice, this list of conditions and the following disclaimer. |
12 | * 2. Redistributions in binary form must reproduce the above copyright |
13 | * notice, this list of conditions and the following disclaimer in the |
14 | * documentation and/or other materials provided with the distribution. |
15 | * |
16 | * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS |
17 | * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED |
18 | * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR |
19 | * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS |
20 | * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR |
21 | * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF |
22 | * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS |
23 | * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN |
24 | * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
25 | * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
26 | * POSSIBILITY OF SUCH DAMAGE. |
27 | */ |
28 | |
29 | /* |
30 | * Passive serialization. |
31 | * |
32 | * Implementation accurately matches the lapsed US patent 4809168, therefore |
33 | * code is patent-free in the United States. Your use of this code is at |
34 | * your own risk. |
35 | * |
36 | * Note for NetBSD developers: all changes to this source file must be |
37 | * approved by the <core>. |
38 | */ |
39 | |
40 | #include <sys/cdefs.h> |
41 | __KERNEL_RCSID(0, "$NetBSD: subr_pserialize.c,v 1.8 2015/06/12 19:18:30 dholland Exp $" ); |
42 | |
43 | #include <sys/param.h> |
44 | |
45 | #include <sys/condvar.h> |
46 | #include <sys/cpu.h> |
47 | #include <sys/evcnt.h> |
48 | #include <sys/kmem.h> |
49 | #include <sys/mutex.h> |
50 | #include <sys/pserialize.h> |
51 | #include <sys/proc.h> |
52 | #include <sys/queue.h> |
53 | #include <sys/xcall.h> |
54 | |
55 | struct pserialize { |
56 | TAILQ_ENTRY(pserialize) psz_chain; |
57 | lwp_t * psz_owner; |
58 | kcpuset_t * psz_target; |
59 | kcpuset_t * psz_pass; |
60 | }; |
61 | |
62 | static u_int psz_work_todo __cacheline_aligned; |
63 | static kmutex_t psz_lock __cacheline_aligned; |
64 | static struct evcnt psz_ev_excl __cacheline_aligned; |
65 | |
66 | /* |
67 | * As defined in "Method 1": |
68 | * q0: "0 MP checkpoints have occured". |
69 | * q1: "1 MP checkpoint has occured". |
70 | * q2: "2 MP checkpoints have occured". |
71 | */ |
72 | static TAILQ_HEAD(, pserialize) psz_queue0 __cacheline_aligned; |
73 | static TAILQ_HEAD(, pserialize) psz_queue1 __cacheline_aligned; |
74 | static TAILQ_HEAD(, pserialize) psz_queue2 __cacheline_aligned; |
75 | |
76 | /* |
77 | * pserialize_init: |
78 | * |
79 | * Initialize passive serialization structures. |
80 | */ |
81 | void |
82 | pserialize_init(void) |
83 | { |
84 | |
85 | psz_work_todo = 0; |
86 | TAILQ_INIT(&psz_queue0); |
87 | TAILQ_INIT(&psz_queue1); |
88 | TAILQ_INIT(&psz_queue2); |
89 | mutex_init(&psz_lock, MUTEX_DEFAULT, IPL_SCHED); |
90 | evcnt_attach_dynamic(&psz_ev_excl, EVCNT_TYPE_MISC, NULL, |
91 | "pserialize" , "exclusive access" ); |
92 | } |
93 | |
94 | /* |
95 | * pserialize_create: |
96 | * |
97 | * Create and initialize a passive serialization object. |
98 | */ |
99 | pserialize_t |
100 | pserialize_create(void) |
101 | { |
102 | pserialize_t psz; |
103 | |
104 | psz = kmem_zalloc(sizeof(struct pserialize), KM_SLEEP); |
105 | kcpuset_create(&psz->psz_target, true); |
106 | kcpuset_create(&psz->psz_pass, true); |
107 | psz->psz_owner = NULL; |
108 | |
109 | return psz; |
110 | } |
111 | |
112 | /* |
113 | * pserialize_destroy: |
114 | * |
115 | * Destroy a passive serialization object. |
116 | */ |
117 | void |
118 | pserialize_destroy(pserialize_t psz) |
119 | { |
120 | |
121 | KASSERT(psz->psz_owner == NULL); |
122 | |
123 | kcpuset_destroy(psz->psz_target); |
124 | kcpuset_destroy(psz->psz_pass); |
125 | kmem_free(psz, sizeof(struct pserialize)); |
126 | } |
127 | |
128 | /* |
129 | * pserialize_perform: |
130 | * |
131 | * Perform the write side of passive serialization. The calling |
132 | * thread holds an exclusive lock on the data object(s) being updated. |
133 | * We wait until every processor in the system has made at least two |
134 | * passes through cpu_switchto(). The wait is made with the caller's |
135 | * update lock held, but is short term. |
136 | */ |
137 | void |
138 | pserialize_perform(pserialize_t psz) |
139 | { |
140 | uint64_t xc; |
141 | |
142 | KASSERT(!cpu_intr_p()); |
143 | KASSERT(!cpu_softintr_p()); |
144 | |
145 | if (__predict_false(panicstr != NULL)) { |
146 | return; |
147 | } |
148 | KASSERT(psz->psz_owner == NULL); |
149 | KASSERT(ncpu > 0); |
150 | |
151 | /* |
152 | * Set up the object and put it onto the queue. The lock |
153 | * activity here provides the necessary memory barrier to |
154 | * make the caller's data update completely visible to |
155 | * other processors. |
156 | */ |
157 | psz->psz_owner = curlwp; |
158 | kcpuset_copy(psz->psz_target, kcpuset_running); |
159 | kcpuset_zero(psz->psz_pass); |
160 | |
161 | mutex_spin_enter(&psz_lock); |
162 | TAILQ_INSERT_TAIL(&psz_queue0, psz, psz_chain); |
163 | psz_work_todo++; |
164 | |
165 | do { |
166 | mutex_spin_exit(&psz_lock); |
167 | |
168 | /* |
169 | * Force some context switch activity on every CPU, as |
170 | * the system may not be busy. Pause to not flood. |
171 | */ |
172 | xc = xc_broadcast(XC_HIGHPRI, (xcfunc_t)nullop, NULL, NULL); |
173 | xc_wait(xc); |
174 | kpause("psrlz" , false, 1, NULL); |
175 | |
176 | mutex_spin_enter(&psz_lock); |
177 | } while (!kcpuset_iszero(psz->psz_target)); |
178 | |
179 | psz_ev_excl.ev_count++; |
180 | mutex_spin_exit(&psz_lock); |
181 | |
182 | psz->psz_owner = NULL; |
183 | } |
184 | |
185 | int |
186 | pserialize_read_enter(void) |
187 | { |
188 | |
189 | KASSERT(!cpu_intr_p()); |
190 | return splsoftserial(); |
191 | } |
192 | |
193 | void |
194 | pserialize_read_exit(int s) |
195 | { |
196 | |
197 | splx(s); |
198 | } |
199 | |
200 | /* |
201 | * pserialize_switchpoint: |
202 | * |
203 | * Monitor system context switch activity. Called from machine |
204 | * independent code after mi_switch() returns. |
205 | */ |
206 | void |
207 | pserialize_switchpoint(void) |
208 | { |
209 | pserialize_t psz, next; |
210 | cpuid_t cid; |
211 | |
212 | /* |
213 | * If no updates pending, bail out. No need to lock in order to |
214 | * test psz_work_todo; the only ill effect of missing an update |
215 | * would be to delay LWPs waiting in pserialize_perform(). That |
216 | * will not happen because updates are on the queue before an |
217 | * xcall is generated (serialization) to tickle every CPU. |
218 | */ |
219 | if (__predict_true(psz_work_todo == 0)) { |
220 | return; |
221 | } |
222 | mutex_spin_enter(&psz_lock); |
223 | cid = cpu_index(curcpu()); |
224 | |
225 | /* |
226 | * At first, scan through the second queue and update each request, |
227 | * if passed all processors, then transfer to the third queue. |
228 | */ |
229 | for (psz = TAILQ_FIRST(&psz_queue1); psz != NULL; psz = next) { |
230 | next = TAILQ_NEXT(psz, psz_chain); |
231 | kcpuset_set(psz->psz_pass, cid); |
232 | if (!kcpuset_match(psz->psz_pass, psz->psz_target)) { |
233 | continue; |
234 | } |
235 | kcpuset_zero(psz->psz_pass); |
236 | TAILQ_REMOVE(&psz_queue1, psz, psz_chain); |
237 | TAILQ_INSERT_TAIL(&psz_queue2, psz, psz_chain); |
238 | } |
239 | /* |
240 | * Scan through the first queue and update each request, |
241 | * if passed all processors, then move to the second queue. |
242 | */ |
243 | for (psz = TAILQ_FIRST(&psz_queue0); psz != NULL; psz = next) { |
244 | next = TAILQ_NEXT(psz, psz_chain); |
245 | kcpuset_set(psz->psz_pass, cid); |
246 | if (!kcpuset_match(psz->psz_pass, psz->psz_target)) { |
247 | continue; |
248 | } |
249 | kcpuset_zero(psz->psz_pass); |
250 | TAILQ_REMOVE(&psz_queue0, psz, psz_chain); |
251 | TAILQ_INSERT_TAIL(&psz_queue1, psz, psz_chain); |
252 | } |
253 | /* |
254 | * Process the third queue: entries have been seen twice on every |
255 | * processor, remove from the queue and notify the updating thread. |
256 | */ |
257 | while ((psz = TAILQ_FIRST(&psz_queue2)) != NULL) { |
258 | TAILQ_REMOVE(&psz_queue2, psz, psz_chain); |
259 | kcpuset_zero(psz->psz_target); |
260 | psz_work_todo--; |
261 | } |
262 | mutex_spin_exit(&psz_lock); |
263 | } |
264 | |