Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | /** |
| 2 | * @file cpu_buffer.c |
| 3 | * |
| 4 | * @remark Copyright 2002 OProfile authors |
| 5 | * @remark Read the file COPYING |
| 6 | * |
| 7 | * @author John Levon <levon@movementarian.org> |
| 8 | * |
| 9 | * Each CPU has a local buffer that stores PC value/event |
| 10 | * pairs. We also log context switches when we notice them. |
| 11 | * Eventually each CPU's buffer is processed into the global |
| 12 | * event buffer by sync_buffer(). |
| 13 | * |
| 14 | * We use a local buffer for two reasons: an NMI or similar |
| 15 | * interrupt cannot synchronise, and high sampling rates |
| 16 | * would lead to catastrophic global synchronisation if |
| 17 | * a global buffer was used. |
| 18 | */ |
| 19 | |
| 20 | #include <linux/sched.h> |
| 21 | #include <linux/oprofile.h> |
| 22 | #include <linux/vmalloc.h> |
| 23 | #include <linux/errno.h> |
| 24 | |
| 25 | #include "event_buffer.h" |
| 26 | #include "cpu_buffer.h" |
| 27 | #include "buffer_sync.h" |
| 28 | #include "oprof.h" |
| 29 | |
| 30 | struct oprofile_cpu_buffer cpu_buffer[NR_CPUS] __cacheline_aligned; |
| 31 | |
| 32 | static void wq_sync_buffer(void *); |
| 33 | |
| 34 | #define DEFAULT_TIMER_EXPIRE (HZ / 10) |
| 35 | static int work_enabled; |
| 36 | |
| 37 | void free_cpu_buffers(void) |
| 38 | { |
| 39 | int i; |
| 40 | |
| 41 | for_each_online_cpu(i) { |
| 42 | vfree(cpu_buffer[i].buffer); |
| 43 | } |
| 44 | } |
| 45 | |
| 46 | |
| 47 | int alloc_cpu_buffers(void) |
| 48 | { |
| 49 | int i; |
| 50 | |
| 51 | unsigned long buffer_size = fs_cpu_buffer_size; |
| 52 | |
| 53 | for_each_online_cpu(i) { |
| 54 | struct oprofile_cpu_buffer * b = &cpu_buffer[i]; |
| 55 | |
| 56 | b->buffer = vmalloc(sizeof(struct op_sample) * buffer_size); |
| 57 | if (!b->buffer) |
| 58 | goto fail; |
| 59 | |
| 60 | b->last_task = NULL; |
| 61 | b->last_is_kernel = -1; |
| 62 | b->tracing = 0; |
| 63 | b->buffer_size = buffer_size; |
| 64 | b->tail_pos = 0; |
| 65 | b->head_pos = 0; |
| 66 | b->sample_received = 0; |
| 67 | b->sample_lost_overflow = 0; |
| 68 | b->cpu = i; |
| 69 | INIT_WORK(&b->work, wq_sync_buffer, b); |
| 70 | } |
| 71 | return 0; |
| 72 | |
| 73 | fail: |
| 74 | free_cpu_buffers(); |
| 75 | return -ENOMEM; |
| 76 | } |
| 77 | |
| 78 | |
| 79 | void start_cpu_work(void) |
| 80 | { |
| 81 | int i; |
| 82 | |
| 83 | work_enabled = 1; |
| 84 | |
| 85 | for_each_online_cpu(i) { |
| 86 | struct oprofile_cpu_buffer * b = &cpu_buffer[i]; |
| 87 | |
| 88 | /* |
| 89 | * Spread the work by 1 jiffy per cpu so they dont all |
| 90 | * fire at once. |
| 91 | */ |
| 92 | schedule_delayed_work_on(i, &b->work, DEFAULT_TIMER_EXPIRE + i); |
| 93 | } |
| 94 | } |
| 95 | |
| 96 | |
| 97 | void end_cpu_work(void) |
| 98 | { |
| 99 | int i; |
| 100 | |
| 101 | work_enabled = 0; |
| 102 | |
| 103 | for_each_online_cpu(i) { |
| 104 | struct oprofile_cpu_buffer * b = &cpu_buffer[i]; |
| 105 | |
| 106 | cancel_delayed_work(&b->work); |
| 107 | } |
| 108 | |
| 109 | flush_scheduled_work(); |
| 110 | } |
| 111 | |
| 112 | |
| 113 | /* Resets the cpu buffer to a sane state. */ |
| 114 | void cpu_buffer_reset(struct oprofile_cpu_buffer * cpu_buf) |
| 115 | { |
| 116 | /* reset these to invalid values; the next sample |
| 117 | * collected will populate the buffer with proper |
| 118 | * values to initialize the buffer |
| 119 | */ |
| 120 | cpu_buf->last_is_kernel = -1; |
| 121 | cpu_buf->last_task = NULL; |
| 122 | } |
| 123 | |
| 124 | |
| 125 | /* compute number of available slots in cpu_buffer queue */ |
| 126 | static unsigned long nr_available_slots(struct oprofile_cpu_buffer const * b) |
| 127 | { |
| 128 | unsigned long head = b->head_pos; |
| 129 | unsigned long tail = b->tail_pos; |
| 130 | |
| 131 | if (tail > head) |
| 132 | return (tail - head) - 1; |
| 133 | |
| 134 | return tail + (b->buffer_size - head) - 1; |
| 135 | } |
| 136 | |
| 137 | |
| 138 | static void increment_head(struct oprofile_cpu_buffer * b) |
| 139 | { |
| 140 | unsigned long new_head = b->head_pos + 1; |
| 141 | |
| 142 | /* Ensure anything written to the slot before we |
| 143 | * increment is visible */ |
| 144 | wmb(); |
| 145 | |
| 146 | if (new_head < b->buffer_size) |
| 147 | b->head_pos = new_head; |
| 148 | else |
| 149 | b->head_pos = 0; |
| 150 | } |
| 151 | |
| 152 | |
| 153 | |
| 154 | |
| 155 | inline static void |
| 156 | add_sample(struct oprofile_cpu_buffer * cpu_buf, |
| 157 | unsigned long pc, unsigned long event) |
| 158 | { |
| 159 | struct op_sample * entry = &cpu_buf->buffer[cpu_buf->head_pos]; |
| 160 | entry->eip = pc; |
| 161 | entry->event = event; |
| 162 | increment_head(cpu_buf); |
| 163 | } |
| 164 | |
| 165 | |
| 166 | inline static void |
| 167 | add_code(struct oprofile_cpu_buffer * buffer, unsigned long value) |
| 168 | { |
| 169 | add_sample(buffer, ESCAPE_CODE, value); |
| 170 | } |
| 171 | |
| 172 | |
| 173 | /* This must be safe from any context. It's safe writing here |
| 174 | * because of the head/tail separation of the writer and reader |
| 175 | * of the CPU buffer. |
| 176 | * |
| 177 | * is_kernel is needed because on some architectures you cannot |
| 178 | * tell if you are in kernel or user space simply by looking at |
| 179 | * pc. We tag this in the buffer by generating kernel enter/exit |
| 180 | * events whenever is_kernel changes |
| 181 | */ |
| 182 | static int log_sample(struct oprofile_cpu_buffer * cpu_buf, unsigned long pc, |
| 183 | int is_kernel, unsigned long event) |
| 184 | { |
| 185 | struct task_struct * task; |
| 186 | |
| 187 | cpu_buf->sample_received++; |
| 188 | |
| 189 | if (nr_available_slots(cpu_buf) < 3) { |
| 190 | cpu_buf->sample_lost_overflow++; |
| 191 | return 0; |
| 192 | } |
| 193 | |
| 194 | is_kernel = !!is_kernel; |
| 195 | |
| 196 | task = current; |
| 197 | |
| 198 | /* notice a switch from user->kernel or vice versa */ |
| 199 | if (cpu_buf->last_is_kernel != is_kernel) { |
| 200 | cpu_buf->last_is_kernel = is_kernel; |
| 201 | add_code(cpu_buf, is_kernel); |
| 202 | } |
| 203 | |
| 204 | /* notice a task switch */ |
| 205 | if (cpu_buf->last_task != task) { |
| 206 | cpu_buf->last_task = task; |
| 207 | add_code(cpu_buf, (unsigned long)task); |
| 208 | } |
| 209 | |
| 210 | add_sample(cpu_buf, pc, event); |
| 211 | return 1; |
| 212 | } |
| 213 | |
| 214 | static int oprofile_begin_trace(struct oprofile_cpu_buffer * cpu_buf) |
| 215 | { |
| 216 | if (nr_available_slots(cpu_buf) < 4) { |
| 217 | cpu_buf->sample_lost_overflow++; |
| 218 | return 0; |
| 219 | } |
| 220 | |
| 221 | add_code(cpu_buf, CPU_TRACE_BEGIN); |
| 222 | cpu_buf->tracing = 1; |
| 223 | return 1; |
| 224 | } |
| 225 | |
| 226 | |
| 227 | static void oprofile_end_trace(struct oprofile_cpu_buffer * cpu_buf) |
| 228 | { |
| 229 | cpu_buf->tracing = 0; |
| 230 | } |
| 231 | |
| 232 | |
| 233 | void oprofile_add_sample(struct pt_regs * const regs, unsigned long event) |
| 234 | { |
| 235 | struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[smp_processor_id()]; |
| 236 | unsigned long pc = profile_pc(regs); |
| 237 | int is_kernel = !user_mode(regs); |
| 238 | |
| 239 | if (!backtrace_depth) { |
| 240 | log_sample(cpu_buf, pc, is_kernel, event); |
| 241 | return; |
| 242 | } |
| 243 | |
| 244 | if (!oprofile_begin_trace(cpu_buf)) |
| 245 | return; |
| 246 | |
| 247 | /* if log_sample() fail we can't backtrace since we lost the source |
| 248 | * of this event */ |
| 249 | if (log_sample(cpu_buf, pc, is_kernel, event)) |
| 250 | oprofile_ops.backtrace(regs, backtrace_depth); |
| 251 | oprofile_end_trace(cpu_buf); |
| 252 | } |
| 253 | |
| 254 | |
| 255 | void oprofile_add_pc(unsigned long pc, int is_kernel, unsigned long event) |
| 256 | { |
| 257 | struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[smp_processor_id()]; |
| 258 | log_sample(cpu_buf, pc, is_kernel, event); |
| 259 | } |
| 260 | |
| 261 | |
| 262 | void oprofile_add_trace(unsigned long pc) |
| 263 | { |
| 264 | struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[smp_processor_id()]; |
| 265 | |
| 266 | if (!cpu_buf->tracing) |
| 267 | return; |
| 268 | |
| 269 | if (nr_available_slots(cpu_buf) < 1) { |
| 270 | cpu_buf->tracing = 0; |
| 271 | cpu_buf->sample_lost_overflow++; |
| 272 | return; |
| 273 | } |
| 274 | |
| 275 | /* broken frame can give an eip with the same value as an escape code, |
| 276 | * abort the trace if we get it */ |
| 277 | if (pc == ESCAPE_CODE) { |
| 278 | cpu_buf->tracing = 0; |
| 279 | cpu_buf->backtrace_aborted++; |
| 280 | return; |
| 281 | } |
| 282 | |
| 283 | add_sample(cpu_buf, pc, 0); |
| 284 | } |
| 285 | |
| 286 | |
| 287 | |
| 288 | /* |
| 289 | * This serves to avoid cpu buffer overflow, and makes sure |
| 290 | * the task mortuary progresses |
| 291 | * |
| 292 | * By using schedule_delayed_work_on and then schedule_delayed_work |
| 293 | * we guarantee this will stay on the correct cpu |
| 294 | */ |
| 295 | static void wq_sync_buffer(void * data) |
| 296 | { |
| 297 | struct oprofile_cpu_buffer * b = data; |
| 298 | if (b->cpu != smp_processor_id()) { |
| 299 | printk("WQ on CPU%d, prefer CPU%d\n", |
| 300 | smp_processor_id(), b->cpu); |
| 301 | } |
| 302 | sync_buffer(b->cpu); |
| 303 | |
| 304 | /* don't re-add the work if we're shutting down */ |
| 305 | if (work_enabled) |
| 306 | schedule_delayed_work(&b->work, DEFAULT_TIMER_EXPIRE); |
| 307 | } |