1 /*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License (the "License").
6 * You may not use this file except in compliance with the License.
7 *
8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9 * or http://www.opensolaris.org/os/licensing.
10 * See the License for the specific language governing permissions
11 * and limitations under the License.
12 *
13 * When distributing Covered Code, include this CDDL HEADER in each
14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15 * If applicable, add the following below this CDDL HEADER, with the
16 * fields enclosed by brackets "[]" replaced with your own identifying
17 * information: Portions Copyright [yyyy] [name of copyright owner]
18 *
19 * CDDL HEADER END
20 */
21 /*
22 * Copyright 2009 Sun Microsystems, Inc. All rights reserved.
23 * Use is subject to license terms.
24 */
25
26 /*
27 * Copyright (c) 2013 by Delphix. All rights reserved.
28 */
29
30 #ifndef _SYS_TXG_IMPL_H
31 #define _SYS_TXG_IMPL_H
32
33 #include <sys/spa.h>
34 #include <sys/txg.h>
35
36 #ifdef __cplusplus
37 extern "C" {
38 #endif
39
40 /*
41 * The tx_cpu structure is a per-cpu structure that is used to track
42 * the number of active transaction holds (tc_count). As transactions
43 * are assigned into a transaction group the appropriate tc_count is
44 * incremented to indicate that there are pending changes that have yet
45 * to quiesce. Consumers evenutally call txg_rele_to_sync() to decrement
46 * the tc_count. A transaction group is not considered quiesced until all
47 * tx_cpu structures have reached a tc_count of zero.
48 *
49 * This structure is a per-cpu structure by design. Updates to this structure
50 * are frequent and concurrent. Having a single structure would result in
51 * heavy lock contention so a per-cpu design was implemented. With the fanned
52 * out mutex design, consumers only need to lock the mutex associated with
53 * thread's cpu.
54 *
55 * The tx_cpu contains two locks, the tc_lock and tc_open_lock.
56 * The tc_lock is used to protect all members of the tx_cpu structure with
57 * the exception of the tc_open_lock. This lock should only be held for a
58 * short period of time, typically when updating the value of tc_count.
59 *
60 * The tc_open_lock protects the tx_open_txg member of the tx_state structure.
61 * This lock is used to ensure that transactions are only assigned into
62 * the current open transaction group. In order to move the current open
63 * transaction group to the quiesce phase, the txg_quiesce thread must
64 * grab all tc_open_locks, increment the tx_open_txg, and drop the locks.
65 * The tc_open_lock is held until the transaction is assigned into the
66 * transaction group. Typically, this is a short operation but if throttling
67 * is occuring it may be held for longer periods of time.
68 */
69 struct tx_cpu {
70 kmutex_t tc_open_lock; /* protects tx_open_txg */
71 kmutex_t tc_lock; /* protects the rest of this struct */
72 kcondvar_t tc_cv[TXG_SIZE];
73 uint64_t tc_count[TXG_SIZE]; /* tx hold count on each txg */
74 list_t tc_callbacks[TXG_SIZE]; /* commit cb list */
75 char tc_pad[8]; /* pad to fill 3 cache lines */
76 };
77
78 /*
79 * The tx_state structure maintains the state information about the different
80 * stages of the pool's transcation groups. A per pool tx_state structure
81 * is used to track this information. The tx_state structure also points to
82 * an array of tx_cpu structures (described above). Although the tx_sync_lock
83 * is used to protect the members of this structure, it is not used to
84 * protect the tx_open_txg. Instead a special lock in the tx_cpu structure
85 * is used. Readers of tx_open_txg must grab the per-cpu tc_open_lock.
86 * Any thread wishing to update tx_open_txg must grab the tc_open_lock on
87 * every cpu (see txg_quiesce()).
88 */
89 typedef struct tx_state {
90 tx_cpu_t *tx_cpu; /* protects access to tx_open_txg */
91 kmutex_t tx_sync_lock; /* protects the rest of this struct */
92 uint64_t tx_open_txg; /* currently open txg id */
93 uint64_t tx_quiesced_txg; /* quiesced txg waiting for sync */
94 uint64_t tx_syncing_txg; /* currently syncing txg id */
95 uint64_t tx_synced_txg; /* last synced txg id */
96
97 uint64_t tx_sync_txg_waiting; /* txg we're waiting to sync */
98 uint64_t tx_quiesce_txg_waiting; /* txg we're waiting to open */
99
100 kcondvar_t tx_sync_more_cv;
101 kcondvar_t tx_sync_done_cv;
102 kcondvar_t tx_quiesce_more_cv;
103 kcondvar_t tx_quiesce_done_cv;
104 kcondvar_t tx_timeout_cv;
105 kcondvar_t tx_exit_cv; /* wait for all threads to exit */
106
107 uint8_t tx_threads; /* number of threads */
108 uint8_t tx_exiting; /* set when we're exiting */
109
110 kthread_t *tx_sync_thread;
111 kthread_t *tx_quiesce_thread;
112
113 taskq_t *tx_commit_cb_taskq; /* commit callback taskq */
114 } tx_state_t;
115
116 #ifdef __cplusplus
117 }
118 #endif
119
120 #endif /* _SYS_TXG_IMPL_H */