include/sys/txg_impl.h

   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 /*
  23  * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
  24  * Use is subject to license terms.
  25  */
  26
  27 /*
  28  * Copyright (c) 2013, 2017 by Delphix. All rights reserved.
  29  */
  30
  31 #ifndef _SYS_TXG_IMPL_H
  32 #define _SYS_TXG_IMPL_H
  33
  34 #include <sys/spa.h>
  35 #include <sys/txg.h>
  36
  37 #ifdef  __cplusplus
  38 extern "C" {
  39 #endif
  40
  41 /*
  42  * The tx_cpu structure is a per-cpu structure that is used to track
  43  * the number of active transaction holds (tc_count). As transactions
  44  * are assigned into a transaction group the appropriate tc_count is
  45  * incremented to indicate that there are pending changes that have yet
  46  * to quiesce. Consumers eventually call txg_rele_to_sync() to decrement
  47  * the tc_count. A transaction group is not considered quiesced until all
  48  * tx_cpu structures have reached a tc_count of zero.
  49  *
  50  * This structure is a per-cpu structure by design. Updates to this structure
  51  * are frequent and concurrent. Having a single structure would result in
  52  * heavy lock contention so a per-cpu design was implemented. With the fanned
  53  * out mutex design, consumers only need to lock the mutex associated with
  54  * thread's cpu.
  55  *
  56  * The tx_cpu contains two locks, the tc_lock and tc_open_lock.
  57  * The tc_lock is used to protect all members of the tx_cpu structure with
  58  * the exception of the tc_open_lock. This lock should only be held for a
  59  * short period of time, typically when updating the value of tc_count.
  60  *
  61  * The tc_open_lock protects the tx_open_txg member of the tx_state structure.
  62  * This lock is used to ensure that transactions are only assigned into
  63  * the current open transaction group. In order to move the current open
  64  * transaction group to the quiesce phase, the txg_quiesce thread must
  65  * grab all tc_open_locks, increment the tx_open_txg, and drop the locks.
  66  * The tc_open_lock is held until the transaction is assigned into the
  67  * transaction group. Typically, this is a short operation but if throttling
  68  * is occurring it may be held for longer periods of time.
  69  */
  70 struct tx_cpu {
  71         kmutex_t        tc_open_lock;   /* protects tx_open_txg */
  72         kmutex_t        tc_lock;        /* protects the rest of this struct */
  73         kcondvar_t      tc_cv[TXG_SIZE];
  74         uint64_t        tc_count[TXG_SIZE];     /* tx hold count on each txg */
  75         list_t          tc_callbacks[TXG_SIZE]; /* commit cb list */
  76         char            tc_pad[8];              /* pad to fill 3 cache lines */
  77 };
  78
  79 /*
  80  * The tx_state structure maintains the state information about the different
  81  * stages of the pool's transaction groups. A per pool tx_state structure
  82  * is used to track this information. The tx_state structure also points to
  83  * an array of tx_cpu structures (described above). Although the tx_sync_lock
  84  * is used to protect the members of this structure, it is not used to
  85  * protect the tx_open_txg. Instead a special lock in the tx_cpu structure
  86  * is used. Readers of tx_open_txg must grab the per-cpu tc_open_lock.
  87  * Any thread wishing to update tx_open_txg must grab the tc_open_lock on
  88  * every cpu (see txg_quiesce()).
  89  */
  90 typedef struct tx_state {
  91         tx_cpu_t        *tx_cpu;        /* protects access to tx_open_txg */
  92         kmutex_t        tx_sync_lock;   /* protects the rest of this struct */
  93
  94         uint64_t        tx_open_txg;    /* currently open txg id */
  95         uint64_t        tx_quiescing_txg; /* currently quiescing txg id */
  96         uint64_t        tx_quiesced_txg; /* quiesced txg waiting for sync */
  97         uint64_t        tx_syncing_txg; /* currently syncing txg id */
  98         uint64_t        tx_synced_txg;  /* last synced txg id */
  99
 100         hrtime_t        tx_open_time;   /* start time of tx_open_txg */
 101
 102         uint64_t        tx_sync_txg_waiting; /* txg we're waiting to sync */
 103         uint64_t        tx_quiesce_txg_waiting; /* txg we're waiting to open */
 104
 105         kcondvar_t      tx_sync_more_cv;
 106         kcondvar_t      tx_sync_done_cv;
 107         kcondvar_t      tx_quiesce_more_cv;
 108         kcondvar_t      tx_quiesce_done_cv;
 109         kcondvar_t      tx_timeout_cv;
 110         kcondvar_t      tx_exit_cv;     /* wait for all threads to exit */
 111
 112         uint8_t         tx_threads;     /* number of threads */
 113         uint8_t         tx_exiting;     /* set when we're exiting */
 114
 115         kthread_t       *tx_sync_thread;
 116         kthread_t       *tx_quiesce_thread;
 117
 118         taskq_t         *tx_commit_cb_taskq; /* commit callback taskq */
 119 } tx_state_t;
 120
 121 #ifdef  __cplusplus
 122 }
 123 #endif
 124
 125 #endif  /* _SYS_TXG_IMPL_H */