libkern/firehose/chunk_private.h

   1 /*
   2  * Copyright (c) 2016 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_APACHE_LICENSE_HEADER_START@
   5  *
   6  * Licensed under the Apache License, Version 2.0 (the "License");
   7  * you may not use this file except in compliance with the License.
   8  * You may obtain a copy of the License at
   9  *
  10  *     http://www.apache.org/licenses/LICENSE-2.0
  11  *
  12  * Unless required by applicable law or agreed to in writing, software
  13  * distributed under the License is distributed on an "AS IS" BASIS,
  14  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  15  * See the License for the specific language governing permissions and
  16  * limitations under the License.
  17  *
  18  * @APPLE_APACHE_LICENSE_HEADER_END@
  19  */
  20
  21 #ifndef __FIREHOSE_CHUNK_PRIVATE__
  22 #define __FIREHOSE_CHUNK_PRIVATE__
  23
  24 #if KERNEL
  25 #include <machine/atomic.h>
  26 #endif
  27 #include <stdatomic.h>
  28 #include <sys/param.h>
  29 #include <os/base.h>
  30 #include "firehose_types_private.h"
  31 #include "tracepoint_private.h"
  32
  33 __BEGIN_DECLS
  34
  35 #define FIREHOSE_CHUNK_SIZE                     4096ul
  36
  37 #define FIREHOSE_CHUNK_POS_ENTRY_OFFS_INC       (1ULL <<  0)
  38 #define FIREHOSE_CHUNK_POS_PRIVATE_OFFS_INC     (1ULL << 16)
  39 #define FIREHOSE_CHUNK_POS_REFCNT_INC           (1ULL << 32)
  40 #define FIREHOSE_CHUNK_POS_FULL_BIT             (1ULL << 56)
  41 #define FIREHOSE_CHUNK_POS_USABLE_FOR_STREAM(pos, stream) \
  42                 ((((pos).fcp_pos >> 48) & 0x1ff) == (uint16_t)stream)
  43
  44 typedef union {
  45         _Atomic(uint64_t) fcp_atomic_pos;
  46         uint64_t fcp_pos;
  47         struct {
  48                 uint16_t fcp_next_entry_offs;
  49                 uint16_t fcp_private_offs;
  50                 uint8_t  fcp_refcnt;
  51                 uint8_t  fcp_qos;
  52                 uint8_t  fcp_stream;
  53                 uint8_t  fcp_flag_full : 1;
  54                 uint8_t  fcp_flag_io : 1;
  55                 uint8_t  fcp_quarantined : 1;
  56                 uint8_t  _fcp_flag_unused : 5;
  57         };
  58 } firehose_chunk_pos_u;
  59
  60 typedef struct firehose_chunk_s {
  61         uint8_t  fc_start[0];
  62         firehose_chunk_pos_u fc_pos;
  63         uint64_t fc_timestamp;
  64         uint8_t  fc_data[FIREHOSE_CHUNK_SIZE - 8 - 8];
  65 } *firehose_chunk_t;
  66
  67 typedef struct firehose_chunk_range_s {
  68         uint16_t fcr_offset; // offset from the start of the chunk
  69         uint16_t fcr_length;
  70 } *firehose_chunk_range_t;
  71
  72 #if defined(KERNEL) || defined(OS_FIREHOSE_SPI)
  73
  74 OS_ALWAYS_INLINE
  75 static inline bool
  76 firehose_chunk_pos_fits(firehose_chunk_pos_u pos, uint16_t size)
  77 {
  78         return pos.fcp_next_entry_offs + size <= pos.fcp_private_offs;
  79 }
  80
  81 #define FIREHOSE_CHUNK_TRY_RESERVE_FAIL_ENQUEUE  (-1)
  82 #define FIREHOSE_CHUNK_TRY_RESERVE_FAIL          ( 0)
  83
  84 OS_ALWAYS_INLINE
  85 static inline long
  86 firehose_chunk_tracepoint_try_reserve(firehose_chunk_t fc, uint64_t stamp,
  87                 firehose_stream_t stream, uint8_t qos, uint16_t pubsize,
  88                 uint16_t privsize, uint8_t **privptr)
  89 {
  90         const uint16_t ft_size = offsetof(struct firehose_tracepoint_s, ft_data);
  91         firehose_chunk_pos_u orig, pos;
  92         bool reservation_failed, stamp_delta_fits;
  93
  94         stamp_delta_fits = ((stamp - fc->fc_timestamp) >> 48) == 0;
  95
  96         // no acquire barrier because the returned space is written to only
  97         os_atomic_rmw_loop(&fc->fc_pos.fcp_atomic_pos,
  98                         orig.fcp_pos, pos.fcp_pos, relaxed, {
  99                 if (orig.fcp_pos == 0) {
 100                         // we acquired a really really old reference, and we probably
 101                         // just faulted in a new page
 102                         os_atomic_rmw_loop_give_up(return FIREHOSE_CHUNK_TRY_RESERVE_FAIL);
 103                 }
 104                 if (!FIREHOSE_CHUNK_POS_USABLE_FOR_STREAM(orig, stream)) {
 105                         // nothing to do if the chunk is full, or the stream doesn't match,
 106                         // in which case the thread probably:
 107                         // - loaded the chunk ref
 108                         // - been suspended a long while
 109                         // - read the chunk to find a very old thing
 110                         os_atomic_rmw_loop_give_up(return FIREHOSE_CHUNK_TRY_RESERVE_FAIL);
 111                 }
 112                 pos = orig;
 113                 if (!firehose_chunk_pos_fits(orig,
 114                                 ft_size + pubsize + privsize) || !stamp_delta_fits) {
 115                         pos.fcp_flag_full = true;
 116                         reservation_failed = true;
 117                 } else {
 118                         if (qos > pos.fcp_qos) pos.fcp_qos = qos;
 119                         // using these *_INC macros is so that the compiler generates better
 120                         // assembly: using the struct individual fields forces the compiler
 121                         // to handle carry propagations, and we know it won't happen
 122                         pos.fcp_pos += roundup(ft_size + pubsize, 8) *
 123                                         FIREHOSE_CHUNK_POS_ENTRY_OFFS_INC;
 124                         pos.fcp_pos -= privsize * FIREHOSE_CHUNK_POS_PRIVATE_OFFS_INC;
 125                         pos.fcp_pos += FIREHOSE_CHUNK_POS_REFCNT_INC;
 126                         const uint16_t minimum_payload_size = 16;
 127                         if (!firehose_chunk_pos_fits(pos,
 128                                         roundup(ft_size + minimum_payload_size , 8))) {
 129                                 // if we can't even have minimum_payload_size bytes of payload
 130                                 // for the next tracepoint, just flush right away
 131                                 pos.fcp_flag_full = true;
 132                         }
 133                         reservation_failed = false;
 134                 }
 135         });
 136
 137         if (reservation_failed) {
 138                 if (pos.fcp_refcnt) {
 139                         // nothing to do, there is a thread writing that will pick up
 140                         // the "FULL" flag on flush and push as a consequence
 141                         return FIREHOSE_CHUNK_TRY_RESERVE_FAIL;
 142                 }
 143                 // caller must enqueue chunk
 144                 return FIREHOSE_CHUNK_TRY_RESERVE_FAIL_ENQUEUE;
 145         }
 146         if (privptr) {
 147                 *privptr = fc->fc_start + pos.fcp_private_offs;
 148         }
 149         return orig.fcp_next_entry_offs;
 150 }
 151
 152 OS_ALWAYS_INLINE
 153 static inline firehose_tracepoint_t
 154 firehose_chunk_tracepoint_begin(firehose_chunk_t fc, uint64_t stamp,
 155                 uint16_t pubsize, uint64_t thread_id, long offset)
 156 {
 157         firehose_tracepoint_t ft = (firehose_tracepoint_t)
 158                         __builtin_assume_aligned(fc->fc_start + offset, 8);
 159         stamp -= fc->fc_timestamp;
 160         stamp |= (uint64_t)pubsize << 48;
 161         // The compiler barrier is needed for userland process death handling, see
 162         // (tracepoint-begin) in libdispatch's firehose_buffer_stream_chunk_install.
 163         atomic_store_explicit(&ft->ft_atomic_stamp_and_length, stamp,
 164                         memory_order_relaxed);
 165         __asm__ __volatile__("" ::: "memory");
 166         ft->ft_thread = thread_id;
 167         return ft;
 168 }
 169
 170 OS_ALWAYS_INLINE
 171 static inline bool
 172 firehose_chunk_tracepoint_end(firehose_chunk_t fc,
 173                 firehose_tracepoint_t ft, firehose_tracepoint_id_u ftid)
 174 {
 175         firehose_chunk_pos_u pos;
 176
 177         atomic_store_explicit(&ft->ft_id.ftid_atomic_value,
 178                         ftid.ftid_value, memory_order_release);
 179         pos.fcp_pos = atomic_fetch_sub_explicit(&fc->fc_pos.fcp_atomic_pos,
 180                         FIREHOSE_CHUNK_POS_REFCNT_INC, memory_order_relaxed);
 181         return pos.fcp_refcnt == 1 && pos.fcp_flag_full;
 182 }
 183
 184 #endif // defined(KERNEL) || defined(OS_FIREHOSE_SPI)
 185
 186 __END_DECLS
 187
 188 #endif // __FIREHOSE_CHUNK_PRIVATE__