drivers/oprofile/cpu_buffer.c

   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 int alloc_cpu_buffers(void)
  47 {
  48         int i;
  49
  50         unsigned long buffer_size = fs_cpu_buffer_size;
  51
  52         for_each_online_cpu(i) {
  53                 struct oprofile_cpu_buffer * b = &cpu_buffer[i];
  54
  55                 b->buffer = vmalloc(sizeof(struct op_sample) * buffer_size);
  56                 if (!b->buffer)
  57                         goto fail;
  58
  59                 b->last_task = NULL;
  60                 b->last_is_kernel = -1;
  61                 b->tracing = 0;
  62                 b->buffer_size = buffer_size;
  63                 b->tail_pos = 0;
  64                 b->head_pos = 0;
  65                 b->sample_received = 0;
  66                 b->sample_lost_overflow = 0;
  67                 b->cpu = i;
  68                 INIT_WORK(&b->work, wq_sync_buffer, b);
  69         }
  70         return 0;
  71
  72 fail:
  73         free_cpu_buffers();
  74         return -ENOMEM;
  75 }
  76
  77 void start_cpu_work(void)
  78 {
  79         int i;
  80
  81         work_enabled = 1;
  82
  83         for_each_online_cpu(i) {
  84                 struct oprofile_cpu_buffer * b = &cpu_buffer[i];
  85
  86                 /*
  87                  * Spread the work by 1 jiffy per cpu so they dont all
  88                  * fire at once.
  89                  */
  90                 schedule_delayed_work_on(i, &b->work, DEFAULT_TIMER_EXPIRE + i);
  91         }
  92 }
  93
  94 void end_cpu_work(void)
  95 {
  96         int i;
  97
  98         work_enabled = 0;
  99
 100         for_each_online_cpu(i) {
 101                 struct oprofile_cpu_buffer * b = &cpu_buffer[i];
 102
 103                 cancel_delayed_work(&b->work);
 104         }
 105
 106         flush_scheduled_work();
 107 }
 108
 109 /* Resets the cpu buffer to a sane state. */
 110 void cpu_buffer_reset(struct oprofile_cpu_buffer * cpu_buf)
 111 {
 112         /* reset these to invalid values; the next sample
 113          * collected will populate the buffer with proper
 114          * values to initialize the buffer
 115          */
 116         cpu_buf->last_is_kernel = -1;
 117         cpu_buf->last_task = NULL;
 118 }
 119
 120 /* compute number of available slots in cpu_buffer queue */
 121 static unsigned long nr_available_slots(struct oprofile_cpu_buffer const * b)
 122 {
 123         unsigned long head = b->head_pos;
 124         unsigned long tail = b->tail_pos;
 125
 126         if (tail > head)
 127                 return (tail - head) - 1;
 128
 129         return tail + (b->buffer_size - head) - 1;
 130 }
 131
 132 static void increment_head(struct oprofile_cpu_buffer * b)
 133 {
 134         unsigned long new_head = b->head_pos + 1;
 135
 136         /* Ensure anything written to the slot before we
 137          * increment is visible */
 138         wmb();
 139
 140         if (new_head < b->buffer_size)
 141                 b->head_pos = new_head;
 142         else
 143                 b->head_pos = 0;
 144 }
 145
 146 static inline void
 147 add_sample(struct oprofile_cpu_buffer * cpu_buf,
 148            unsigned long pc, unsigned long event)
 149 {
 150         struct op_sample * entry = &cpu_buf->buffer[cpu_buf->head_pos];
 151         entry->eip = pc;
 152         entry->event = event;
 153         increment_head(cpu_buf);
 154 }
 155
 156 static inline void
 157 add_code(struct oprofile_cpu_buffer * buffer, unsigned long value)
 158 {
 159         add_sample(buffer, ESCAPE_CODE, value);
 160 }
 161
 162 /* This must be safe from any context. It's safe writing here
 163  * because of the head/tail separation of the writer and reader
 164  * of the CPU buffer.
 165  *
 166  * is_kernel is needed because on some architectures you cannot
 167  * tell if you are in kernel or user space simply by looking at
 168  * pc. We tag this in the buffer by generating kernel enter/exit
 169  * events whenever is_kernel changes
 170  */
 171 static int log_sample(struct oprofile_cpu_buffer * cpu_buf, unsigned long pc,
 172                       int is_kernel, unsigned long event)
 173 {
 174         struct task_struct * task;
 175
 176         cpu_buf->sample_received++;
 177
 178         if (nr_available_slots(cpu_buf) < 3) {
 179                 cpu_buf->sample_lost_overflow++;
 180                 return 0;
 181         }
 182
 183         is_kernel = !!is_kernel;
 184
 185         task = current;
 186
 187         /* notice a switch from user->kernel or vice versa */
 188         if (cpu_buf->last_is_kernel != is_kernel) {
 189                 cpu_buf->last_is_kernel = is_kernel;
 190                 add_code(cpu_buf, is_kernel);
 191         }
 192
 193         /* notice a task switch */
 194         if (cpu_buf->last_task != task) {
 195                 cpu_buf->last_task = task;
 196                 add_code(cpu_buf, (unsigned long)task);
 197         }
 198
 199         add_sample(cpu_buf, pc, event);
 200         return 1;
 201 }
 202
 203 static int oprofile_begin_trace(struct oprofile_cpu_buffer * cpu_buf)
 204 {
 205         if (nr_available_slots(cpu_buf) < 4) {
 206                 cpu_buf->sample_lost_overflow++;
 207                 return 0;
 208         }
 209
 210         add_code(cpu_buf, CPU_TRACE_BEGIN);
 211         cpu_buf->tracing = 1;
 212         return 1;
 213 }
 214
 215 static void oprofile_end_trace(struct oprofile_cpu_buffer * cpu_buf)
 216 {
 217         cpu_buf->tracing = 0;
 218 }
 219
 220 void oprofile_add_sample(struct pt_regs * const regs, unsigned long event)
 221 {
 222         struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[smp_processor_id()];
 223         unsigned long pc = profile_pc(regs);
 224         int is_kernel = !user_mode(regs);
 225
 226         if (!backtrace_depth) {
 227                 log_sample(cpu_buf, pc, is_kernel, event);
 228                 return;
 229         }
 230
 231         if (!oprofile_begin_trace(cpu_buf))
 232                 return;
 233
 234         /* if log_sample() fail we can't backtrace since we lost the source
 235          * of this event */
 236         if (log_sample(cpu_buf, pc, is_kernel, event))
 237                 oprofile_ops.backtrace(regs, backtrace_depth);
 238         oprofile_end_trace(cpu_buf);
 239 }
 240
 241 void oprofile_add_pc(unsigned long pc, int is_kernel, unsigned long event)
 242 {
 243         struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[smp_processor_id()];
 244         log_sample(cpu_buf, pc, is_kernel, event);
 245 }
 246
 247 void oprofile_add_trace(unsigned long pc)
 248 {
 249         struct oprofile_cpu_buffer * cpu_buf = &cpu_buffer[smp_processor_id()];
 250
 251         if (!cpu_buf->tracing)
 252                 return;
 253
 254         if (nr_available_slots(cpu_buf) < 1) {
 255                 cpu_buf->tracing = 0;
 256                 cpu_buf->sample_lost_overflow++;
 257                 return;
 258         }
 259
 260         /* broken frame can give an eip with the same value as an escape code,
 261          * abort the trace if we get it */
 262         if (pc == ESCAPE_CODE) {
 263                 cpu_buf->tracing = 0;
 264                 cpu_buf->backtrace_aborted++;
 265                 return;
 266         }
 267
 268         add_sample(cpu_buf, pc, 0);
 269 }
 270
 271 /*
 272  * This serves to avoid cpu buffer overflow, and makes sure
 273  * the task mortuary progresses
 274  *
 275  * By using schedule_delayed_work_on and then schedule_delayed_work
 276  * we guarantee this will stay on the correct cpu
 277  */
 278 static void wq_sync_buffer(void * data)
 279 {
 280         struct oprofile_cpu_buffer * b = data;
 281         if (b->cpu != smp_processor_id()) {
 282                 printk("WQ on CPU%d, prefer CPU%d\n",
 283                        smp_processor_id(), b->cpu);
 284         }
 285         sync_buffer(b->cpu);
 286
 287         /* don't re-add the work if we're shutting down */
 288         if (work_enabled)
 289                 schedule_delayed_work(&b->work, DEFAULT_TIMER_EXPIRE);
 290 }