net/rds/ib_ring.c

   1 /*
   2  * Copyright (c) 2006 Oracle.  All rights reserved.
   3  *
   4  * This software is available to you under a choice of one of two
   5  * licenses.  You may choose to be licensed under the terms of the GNU
   6  * General Public License (GPL) Version 2, available from the file
   7  * COPYING in the main directory of this source tree, or the
   8  * OpenIB.org BSD license below:
   9  *
  10  *     Redistribution and use in source and binary forms, with or
  11  *     without modification, are permitted provided that the following
  12  *     conditions are met:
  13  *
  14  *      - Redistributions of source code must retain the above
  15  *        copyright notice, this list of conditions and the following
  16  *        disclaimer.
  17  *
  18  *      - Redistributions in binary form must reproduce the above
  19  *        copyright notice, this list of conditions and the following
  20  *        disclaimer in the documentation and/or other materials
  21  *        provided with the distribution.
  22  *
  23  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  24  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  25  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  26  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  27  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  28  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  29  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  30  * SOFTWARE.
  31  *
  32  */
  33 #include <linux/kernel.h>
  34
  35 #include "rds.h"
  36 #include "ib.h"
  37
  38 /*
  39  * Locking for IB rings.
  40  * We assume that allocation is always protected by a mutex
  41  * in the caller (this is a valid assumption for the current
  42  * implementation).
  43  *
  44  * Freeing always happens in an interrupt, and hence only
  45  * races with allocations, but not with other free()s.
  46  *
  47  * The interaction between allocation and freeing is that
  48  * the alloc code has to determine the number of free entries.
  49  * To this end, we maintain two counters; an allocation counter
  50  * and a free counter. Both are allowed to run freely, and wrap
  51  * around.
  52  * The number of used entries is always (alloc_ctr - free_ctr) % NR.
  53  *
  54  * The current implementation makes free_ctr atomic. When the
  55  * caller finds an allocation fails, it should set an "alloc fail"
  56  * bit and retry the allocation. The "alloc fail" bit essentially tells
  57  * the CQ completion handlers to wake it up after freeing some
  58  * more entries.
  59  */
  60
  61 /*
  62  * This only happens on shutdown.
  63  */
  64 DECLARE_WAIT_QUEUE_HEAD(rds_ib_ring_empty_wait);
  65
  66 void rds_ib_ring_init(struct rds_ib_work_ring *ring, u32 nr)
  67 {
  68         memset(ring, 0, sizeof(*ring));
  69         ring->w_nr = nr;
  70         rdsdebug("ring %p nr %u\n", ring, ring->w_nr);
  71 }
  72
  73 static inline u32 __rds_ib_ring_used(struct rds_ib_work_ring *ring)
  74 {
  75         u32 diff;
  76
  77         /* This assumes that atomic_t has at least as many bits as u32 */
  78         diff = ring->w_alloc_ctr - (u32) atomic_read(&ring->w_free_ctr);
  79         BUG_ON(diff > ring->w_nr);
  80
  81         return diff;
  82 }
  83
  84 void rds_ib_ring_resize(struct rds_ib_work_ring *ring, u32 nr)
  85 {
  86         /* We only ever get called from the connection setup code,
  87          * prior to creating the QP. */
  88         BUG_ON(__rds_ib_ring_used(ring));
  89         ring->w_nr = nr;
  90 }
  91
  92 static int __rds_ib_ring_empty(struct rds_ib_work_ring *ring)
  93 {
  94         return __rds_ib_ring_used(ring) == 0;
  95 }
  96
  97 u32 rds_ib_ring_alloc(struct rds_ib_work_ring *ring, u32 val, u32 *pos)
  98 {
  99         u32 ret = 0, avail;
 100
 101         avail = ring->w_nr - __rds_ib_ring_used(ring);
 102
 103         rdsdebug("ring %p val %u next %u free %u\n", ring, val,
 104                  ring->w_alloc_ptr, avail);
 105
 106         if (val && avail) {
 107                 ret = min(val, avail);
 108                 *pos = ring->w_alloc_ptr;
 109
 110                 ring->w_alloc_ptr = (ring->w_alloc_ptr + ret) % ring->w_nr;
 111                 ring->w_alloc_ctr += ret;
 112         }
 113
 114         return ret;
 115 }
 116
 117 void rds_ib_ring_free(struct rds_ib_work_ring *ring, u32 val)
 118 {
 119         ring->w_free_ptr = (ring->w_free_ptr + val) % ring->w_nr;
 120         atomic_add(val, &ring->w_free_ctr);
 121
 122         if (__rds_ib_ring_empty(ring) &&
 123             waitqueue_active(&rds_ib_ring_empty_wait))
 124                 wake_up(&rds_ib_ring_empty_wait);
 125 }
 126
 127 void rds_ib_ring_unalloc(struct rds_ib_work_ring *ring, u32 val)
 128 {
 129         ring->w_alloc_ptr = (ring->w_alloc_ptr - val) % ring->w_nr;
 130         ring->w_alloc_ctr -= val;
 131 }
 132
 133 int rds_ib_ring_empty(struct rds_ib_work_ring *ring)
 134 {
 135         return __rds_ib_ring_empty(ring);
 136 }
 137
 138 int rds_ib_ring_low(struct rds_ib_work_ring *ring)
 139 {
 140         return __rds_ib_ring_used(ring) <= (ring->w_nr >> 1);
 141 }
 142
 143 /*
 144  * returns the oldest alloced ring entry.  This will be the next one
 145  * freed.  This can't be called if there are none allocated.
 146  */
 147 u32 rds_ib_ring_oldest(struct rds_ib_work_ring *ring)
 148 {
 149         return ring->w_free_ptr;
 150 }
 151
 152 /*
 153  * returns the number of completed work requests.
 154  */
 155
 156 u32 rds_ib_ring_completed(struct rds_ib_work_ring *ring, u32 wr_id, u32 oldest)
 157 {
 158         u32 ret;
 159
 160         if (oldest <= (unsigned long long)wr_id)
 161                 ret = (unsigned long long)wr_id - oldest + 1;
 162         else
 163                 ret = ring->w_nr - oldest + (unsigned long long)wr_id + 1;
 164
 165         rdsdebug("ring %p ret %u wr_id %u oldest %u\n", ring, ret,
 166                  wr_id, oldest);
 167         return ret;
 168 }