lib/ringbuffer/config.h

   1 /* SPDX-License-Identifier: (GPL-2.0-only OR LGPL-2.1-only)
   2  *
   3  * lib/ringbuffer/config.h
   4  *
   5  * Ring buffer configuration header. Note: after declaring the standard inline
   6  * functions, clients should also include linux/ringbuffer/api.h.
   7  *
   8  * Copyright (C) 2010-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   9  */
  10
  11 #ifndef _LIB_RING_BUFFER_CONFIG_H
  12 #define _LIB_RING_BUFFER_CONFIG_H
  13
  14 #include <linux/types.h>
  15 #include <linux/percpu.h>
  16 #include <lib/align.h>
  17 #include <lttng-tracer-core.h>
  18
  19 struct lib_ring_buffer;
  20 struct channel;
  21 struct lib_ring_buffer_config;
  22 struct lib_ring_buffer_ctx;
  23
  24 /*
  25  * Ring buffer client callbacks. Only used by slow path, never on fast path.
  26  * For the fast path, record_header_size(), ring_buffer_clock_read() should be
  27  * provided as inline functions too.  These may simply return 0 if not used by
  28  * the client.
  29  */
  30 struct lib_ring_buffer_client_cb {
  31         /* Mandatory callbacks */
  32
  33         /* A static inline version is also required for fast path */
  34         u64 (*ring_buffer_clock_read) (struct channel *chan);
  35         size_t (*record_header_size) (const struct lib_ring_buffer_config *config,
  36                                       struct channel *chan, size_t offset,
  37                                       size_t *pre_header_padding,
  38                                       struct lib_ring_buffer_ctx *ctx,
  39                                       void *client_ctx);
  40
  41         /* Slow path only, at subbuffer switch */
  42         size_t (*subbuffer_header_size) (void);
  43         void (*buffer_begin) (struct lib_ring_buffer *buf, u64 tsc,
  44                               unsigned int subbuf_idx);
  45         void (*buffer_end) (struct lib_ring_buffer *buf, u64 tsc,
  46                             unsigned int subbuf_idx, unsigned long data_size);
  47
  48         /* Optional callbacks (can be set to NULL) */
  49
  50         /* Called at buffer creation/finalize */
  51         int (*buffer_create) (struct lib_ring_buffer *buf, void *priv,
  52                               int cpu, const char *name);
  53         /*
  54          * Clients should guarantee that no new reader handle can be opened
  55          * after finalize.
  56          */
  57         void (*buffer_finalize) (struct lib_ring_buffer *buf, void *priv, int cpu);
  58
  59         /*
  60          * Extract header length, payload length and timestamp from event
  61          * record. Used by buffer iterators. Timestamp is only used by channel
  62          * iterator.
  63          */
  64         void (*record_get) (const struct lib_ring_buffer_config *config,
  65                             struct channel *chan, struct lib_ring_buffer *buf,
  66                             size_t offset, size_t *header_len,
  67                             size_t *payload_len, u64 *timestamp);
  68 };
  69
  70 /*
  71  * Ring buffer instance configuration.
  72  *
  73  * Declare as "static const" within the client object to ensure the inline fast
  74  * paths can be optimized.
  75  *
  76  * alloc/sync pairs:
  77  *
  78  * RING_BUFFER_ALLOC_PER_CPU and RING_BUFFER_SYNC_PER_CPU :
  79  *   Per-cpu buffers with per-cpu synchronization. Tracing must be performed
  80  *   with preemption disabled (lib_ring_buffer_get_cpu() and
  81  *   lib_ring_buffer_put_cpu()).
  82  *
  83  * RING_BUFFER_ALLOC_PER_CPU and RING_BUFFER_SYNC_GLOBAL :
  84  *   Per-cpu buffer with global synchronization. Tracing can be performed with
  85  *   preemption enabled, statistically stays on the local buffers.
  86  *
  87  * RING_BUFFER_ALLOC_GLOBAL and RING_BUFFER_SYNC_PER_CPU :
  88  *   Should only be used for buffers belonging to a single thread or protected
  89  *   by mutual exclusion by the client. Note that periodical sub-buffer switch
  90  *   should be disabled in this kind of configuration.
  91  *
  92  * RING_BUFFER_ALLOC_GLOBAL and RING_BUFFER_SYNC_GLOBAL :
  93  *   Global shared buffer with global synchronization.
  94  *
  95  * wakeup:
  96  *
  97  * RING_BUFFER_WAKEUP_BY_TIMER uses per-cpu timers to poll the
  98  * buffers and wake up readers if data is ready. Mainly useful for tracers which
  99  * don't want to call into the wakeup code on the tracing path. Use in
 100  * combination with "read_timer_interval" channel_create() argument.
 101  *
 102  * RING_BUFFER_WAKEUP_BY_WRITER directly wakes up readers when a subbuffer is
 103  * ready to read. Lower latencies before the reader is woken up. Mainly suitable
 104  * for drivers.
 105  *
 106  * RING_BUFFER_WAKEUP_NONE does not perform any wakeup whatsoever. The client
 107  * has the responsibility to perform wakeups.
 108  */
 109 struct lib_ring_buffer_config {
 110         enum {
 111                 RING_BUFFER_ALLOC_PER_CPU,
 112                 RING_BUFFER_ALLOC_GLOBAL,
 113         } alloc;
 114         enum {
 115                 RING_BUFFER_SYNC_PER_CPU,       /* Wait-free */
 116                 RING_BUFFER_SYNC_GLOBAL,        /* Lock-free */
 117         } sync;
 118         enum {
 119                 RING_BUFFER_OVERWRITE,          /* Overwrite when buffer full */
 120                 RING_BUFFER_DISCARD,            /* Discard when buffer full */
 121         } mode;
 122         enum {
 123                 RING_BUFFER_SPLICE,
 124                 RING_BUFFER_MMAP,
 125                 RING_BUFFER_READ,               /* TODO */
 126                 RING_BUFFER_ITERATOR,
 127                 RING_BUFFER_NONE,
 128         } output;
 129         enum {
 130                 RING_BUFFER_PAGE,
 131                 RING_BUFFER_VMAP,               /* TODO */
 132                 RING_BUFFER_STATIC,             /* TODO */
 133         } backend;
 134         enum {
 135                 RING_BUFFER_NO_OOPS_CONSISTENCY,
 136                 RING_BUFFER_OOPS_CONSISTENCY,
 137         } oops;
 138         enum {
 139                 RING_BUFFER_IPI_BARRIER,
 140                 RING_BUFFER_NO_IPI_BARRIER,
 141         } ipi;
 142         enum {
 143                 RING_BUFFER_WAKEUP_BY_TIMER,    /* wake up performed by timer */
 144                 RING_BUFFER_WAKEUP_BY_WRITER,   /*
 145                                                  * writer wakes up reader,
 146                                                  * not lock-free
 147                                                  * (takes spinlock).
 148                                                  */
 149         } wakeup;
 150         /*
 151          * tsc_bits: timestamp bits saved at each record.
 152          *   0 and 64 disable the timestamp compression scheme.
 153          */
 154         unsigned int tsc_bits;
 155         struct lib_ring_buffer_client_cb cb;
 156 };
 157
 158 /*
 159  * ring buffer context
 160  *
 161  * Context passed to lib_ring_buffer_reserve(), lib_ring_buffer_commit(),
 162  * lib_ring_buffer_try_discard_reserve(), lib_ring_buffer_align_ctx() and
 163  * lib_ring_buffer_write().
 164  */
 165 struct lib_ring_buffer_ctx {
 166         /* input received by lib_ring_buffer_reserve(), saved here. */
 167         struct channel *chan;           /* channel */
 168         void *priv;                     /* client private data */
 169         size_t data_size;               /* size of payload */
 170         int largest_align;              /*
 171                                          * alignment of the largest element
 172                                          * in the payload
 173                                          */
 174         int cpu;                        /* processor id */
 175
 176         /* output from lib_ring_buffer_reserve() */
 177         struct lib_ring_buffer *buf;    /*
 178                                          * buffer corresponding to processor id
 179                                          * for this channel
 180                                          */
 181         size_t slot_size;               /* size of the reserved slot */
 182         unsigned long buf_offset;       /* offset following the record header */
 183         unsigned long pre_offset;       /*
 184                                          * Initial offset position _before_
 185                                          * the record is written. Positioned
 186                                          * prior to record header alignment
 187                                          * padding.
 188                                          */
 189         u64 tsc;                        /* time-stamp counter value */
 190         unsigned int rflags;            /* reservation flags */
 191         /* Cache backend pages pointer chasing. */
 192         struct lib_ring_buffer_backend_pages *backend_pages;
 193 };
 194
 195 /**
 196  * lib_ring_buffer_ctx_init - initialize ring buffer context
 197  * @ctx: ring buffer context to initialize
 198  * @chan: channel
 199  * @priv: client private data
 200  * @data_size: size of record data payload. It must be greater than 0.
 201  * @largest_align: largest alignment within data payload types
 202  * @cpu: processor id
 203  */
 204 static inline
 205 void lib_ring_buffer_ctx_init(struct lib_ring_buffer_ctx *ctx,
 206                               struct channel *chan, void *priv,
 207                               size_t data_size, int largest_align,
 208                               int cpu)
 209 {
 210         ctx->chan = chan;
 211         ctx->priv = priv;
 212         ctx->data_size = data_size;
 213         ctx->largest_align = largest_align;
 214         ctx->cpu = cpu;
 215         ctx->rflags = 0;
 216         ctx->backend_pages = NULL;
 217 }
 218
 219 /*
 220  * Reservation flags.
 221  *
 222  * RING_BUFFER_RFLAG_FULL_TSC
 223  *
 224  * This flag is passed to record_header_size() and to the primitive used to
 225  * write the record header. It indicates that the full 64-bit time value is
 226  * needed in the record header. If this flag is not set, the record header needs
 227  * only to contain "tsc_bits" bit of time value.
 228  *
 229  * Reservation flags can be added by the client, starting from
 230  * "(RING_BUFFER_FLAGS_END << 0)". It can be used to pass information from
 231  * record_header_size() to lib_ring_buffer_write_record_header().
 232  */
 233 #define RING_BUFFER_RFLAG_FULL_TSC              (1U << 0)
 234 #define RING_BUFFER_RFLAG_END                   (1U << 1)
 235
 236 #ifndef LTTNG_TRACER_CORE_H
 237 #error "lttng-tracer-core.h is needed for RING_BUFFER_ALIGN define"
 238 #endif
 239
 240 /*
 241  * We need to define RING_BUFFER_ALIGN_ATTR so it is known early at
 242  * compile-time. We have to duplicate the "config->align" information and the
 243  * definition here because config->align is used both in the slow and fast
 244  * paths, but RING_BUFFER_ALIGN_ATTR is only available for the client code.
 245  */
 246 #ifdef RING_BUFFER_ALIGN
 247
 248 # define RING_BUFFER_ALIGN_ATTR         /* Default arch alignment */
 249
 250 /*
 251  * Calculate the offset needed to align the type.
 252  * size_of_type must be non-zero.
 253  */
 254 static inline
 255 unsigned int lib_ring_buffer_align(size_t align_drift, size_t size_of_type)
 256 {
 257         return offset_align(align_drift, size_of_type);
 258 }
 259
 260 #else
 261
 262 # define RING_BUFFER_ALIGN_ATTR __attribute__((packed))
 263
 264 /*
 265  * Calculate the offset needed to align the type.
 266  * size_of_type must be non-zero.
 267  */
 268 static inline
 269 unsigned int lib_ring_buffer_align(size_t align_drift, size_t size_of_type)
 270 {
 271         return 0;
 272 }
 273
 274 #endif
 275
 276 /**
 277  * lib_ring_buffer_align_ctx - Align context offset on "alignment"
 278  * @ctx: ring buffer context.
 279  */
 280 static inline
 281 void lib_ring_buffer_align_ctx(struct lib_ring_buffer_ctx *ctx,
 282                            size_t alignment)
 283 {
 284         ctx->buf_offset += lib_ring_buffer_align(ctx->buf_offset,
 285                                                  alignment);
 286 }
 287
 288 /*
 289  * lib_ring_buffer_check_config() returns 0 on success.
 290  * Used internally to check for valid configurations at channel creation.
 291  */
 292 static inline
 293 int lib_ring_buffer_check_config(const struct lib_ring_buffer_config *config,
 294                              unsigned int switch_timer_interval,
 295                              unsigned int read_timer_interval)
 296 {
 297         if (config->alloc == RING_BUFFER_ALLOC_GLOBAL
 298             && config->sync == RING_BUFFER_SYNC_PER_CPU
 299             && switch_timer_interval)
 300                 return -EINVAL;
 301         return 0;
 302 }
 303
 304 #include <wrapper/ringbuffer/vatomic.h>
 305
 306 #endif /* _LIB_RING_BUFFER_CONFIG_H */