kernel/trace/trace_branch.c

   1 /*
   2  * unlikely profiler
   3  *
   4  * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
   5  */
   6 #include <linux/kallsyms.h>
   7 #include <linux/seq_file.h>
   8 #include <linux/spinlock.h>
   9 #include <linux/debugfs.h>
  10 #include <linux/uaccess.h>
  11 #include <linux/module.h>
  12 #include <linux/ftrace.h>
  13 #include <linux/hash.h>
  14 #include <linux/fs.h>
  15 #include <asm/local.h>
  16 #include "trace.h"
  17
  18 #ifdef CONFIG_BRANCH_TRACER
  19
  20 static int branch_tracing_enabled __read_mostly;
  21 static DEFINE_MUTEX(branch_tracing_mutex);
  22 static struct trace_array *branch_tracer;
  23
  24 static void
  25 probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
  26 {
  27         struct trace_array *tr = branch_tracer;
  28         struct ring_buffer_event *event;
  29         struct trace_branch *entry;
  30         unsigned long flags, irq_flags;
  31         int cpu, pc;
  32         const char *p;
  33
  34         /*
  35          * I would love to save just the ftrace_likely_data pointer, but
  36          * this code can also be used by modules. Ugly things can happen
  37          * if the module is unloaded, and then we go and read the
  38          * pointer.  This is slower, but much safer.
  39          */
  40
  41         if (unlikely(!tr))
  42                 return;
  43
  44         local_irq_save(flags);
  45         cpu = raw_smp_processor_id();
  46         if (atomic_inc_return(&tr->data[cpu]->disabled) != 1)
  47                 goto out;
  48
  49         event = ring_buffer_lock_reserve(tr->buffer, sizeof(*entry),
  50                                          &irq_flags);
  51         if (!event)
  52                 goto out;
  53
  54         pc = preempt_count();
  55         entry   = ring_buffer_event_data(event);
  56         tracing_generic_entry_update(&entry->ent, flags, pc);
  57         entry->ent.type         = TRACE_BRANCH;
  58
  59         /* Strip off the path, only save the file */
  60         p = f->file + strlen(f->file);
  61         while (p >= f->file && *p != '/')
  62                 p--;
  63         p++;
  64
  65         strncpy(entry->func, f->func, TRACE_FUNC_SIZE);
  66         strncpy(entry->file, p, TRACE_FILE_SIZE);
  67         entry->func[TRACE_FUNC_SIZE] = 0;
  68         entry->file[TRACE_FILE_SIZE] = 0;
  69         entry->line = f->line;
  70         entry->correct = val == expect;
  71
  72         ring_buffer_unlock_commit(tr->buffer, event, irq_flags);
  73
  74  out:
  75         atomic_dec(&tr->data[cpu]->disabled);
  76         local_irq_restore(flags);
  77 }
  78
  79 static inline
  80 void trace_likely_condition(struct ftrace_branch_data *f, int val, int expect)
  81 {
  82         if (!branch_tracing_enabled)
  83                 return;
  84
  85         probe_likely_condition(f, val, expect);
  86 }
  87
  88 int enable_branch_tracing(struct trace_array *tr)
  89 {
  90         int ret = 0;
  91
  92         mutex_lock(&branch_tracing_mutex);
  93         branch_tracer = tr;
  94         /*
  95          * Must be seen before enabling. The reader is a condition
  96          * where we do not need a matching rmb()
  97          */
  98         smp_wmb();
  99         branch_tracing_enabled++;
 100         mutex_unlock(&branch_tracing_mutex);
 101
 102         return ret;
 103 }
 104
 105 void disable_branch_tracing(void)
 106 {
 107         mutex_lock(&branch_tracing_mutex);
 108
 109         if (!branch_tracing_enabled)
 110                 goto out_unlock;
 111
 112         branch_tracing_enabled--;
 113
 114  out_unlock:
 115         mutex_unlock(&branch_tracing_mutex);
 116 }
 117
 118 static void start_branch_trace(struct trace_array *tr)
 119 {
 120         enable_branch_tracing(tr);
 121 }
 122
 123 static void stop_branch_trace(struct trace_array *tr)
 124 {
 125         disable_branch_tracing();
 126 }
 127
 128 static void branch_trace_init(struct trace_array *tr)
 129 {
 130         int cpu;
 131
 132         for_each_online_cpu(cpu)
 133                 tracing_reset(tr, cpu);
 134
 135         start_branch_trace(tr);
 136 }
 137
 138 static void branch_trace_reset(struct trace_array *tr)
 139 {
 140         stop_branch_trace(tr);
 141 }
 142
 143 struct tracer branch_trace __read_mostly =
 144 {
 145         .name           = "branch",
 146         .init           = branch_trace_init,
 147         .reset          = branch_trace_reset,
 148 #ifdef CONFIG_FTRACE_SELFTEST
 149         .selftest       = trace_selftest_startup_branch,
 150 #endif
 151 };
 152
 153 __init static int init_branch_trace(void)
 154 {
 155         return register_tracer(&branch_trace);
 156 }
 157
 158 device_initcall(init_branch_trace);
 159 #else
 160 static inline
 161 void trace_likely_condition(struct ftrace_branch_data *f, int val, int expect)
 162 {
 163 }
 164 #endif /* CONFIG_BRANCH_TRACER */
 165
 166 void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect)
 167 {
 168         /*
 169          * I would love to have a trace point here instead, but the
 170          * trace point code is so inundated with unlikely and likely
 171          * conditions that the recursive nightmare that exists is too
 172          * much to try to get working. At least for now.
 173          */
 174         trace_likely_condition(f, val, expect);
 175
 176         /* FIXME: Make this atomic! */
 177         if (val == expect)
 178                 f->correct++;
 179         else
 180                 f->incorrect++;
 181 }
 182 EXPORT_SYMBOL(ftrace_likely_update);
 183
 184 struct ftrace_pointer {
 185         void            *start;
 186         void            *stop;
 187 };
 188
 189 static void *
 190 t_next(struct seq_file *m, void *v, loff_t *pos)
 191 {
 192         struct ftrace_pointer *f = m->private;
 193         struct ftrace_branch_data *p = v;
 194
 195         (*pos)++;
 196
 197         if (v == (void *)1)
 198                 return f->start;
 199
 200         ++p;
 201
 202         if ((void *)p >= (void *)f->stop)
 203                 return NULL;
 204
 205         return p;
 206 }
 207
 208 static void *t_start(struct seq_file *m, loff_t *pos)
 209 {
 210         void *t = (void *)1;
 211         loff_t l = 0;
 212
 213         for (; t && l < *pos; t = t_next(m, t, &l))
 214                 ;
 215
 216         return t;
 217 }
 218
 219 static void t_stop(struct seq_file *m, void *p)
 220 {
 221 }
 222
 223 static int t_show(struct seq_file *m, void *v)
 224 {
 225         struct ftrace_branch_data *p = v;
 226         const char *f;
 227         unsigned long percent;
 228
 229         if (v == (void *)1) {
 230                 seq_printf(m, " correct incorrect  %% "
 231                               "       Function                "
 232                               "  File              Line\n"
 233                               " ------- ---------  - "
 234                               "       --------                "
 235                               "  ----              ----\n");
 236                 return 0;
 237         }
 238
 239         /* Only print the file, not the path */
 240         f = p->file + strlen(p->file);
 241         while (f >= p->file && *f != '/')
 242                 f--;
 243         f++;
 244
 245         if (p->correct) {
 246                 percent = p->incorrect * 100;
 247                 percent /= p->correct + p->incorrect;
 248         } else
 249                 percent = p->incorrect ? 100 : 0;
 250
 251         seq_printf(m, "%8lu %8lu %3lu ", p->correct, p->incorrect, percent);
 252         seq_printf(m, "%-30.30s %-20.20s %d\n", p->func, f, p->line);
 253         return 0;
 254 }
 255
 256 static struct seq_operations tracing_likely_seq_ops = {
 257         .start          = t_start,
 258         .next           = t_next,
 259         .stop           = t_stop,
 260         .show           = t_show,
 261 };
 262
 263 static int tracing_likely_open(struct inode *inode, struct file *file)
 264 {
 265         int ret;
 266
 267         ret = seq_open(file, &tracing_likely_seq_ops);
 268         if (!ret) {
 269                 struct seq_file *m = file->private_data;
 270                 m->private = (void *)inode->i_private;
 271         }
 272
 273         return ret;
 274 }
 275
 276 static struct file_operations tracing_likely_fops = {
 277         .open           = tracing_likely_open,
 278         .read           = seq_read,
 279         .llseek         = seq_lseek,
 280 };
 281
 282 extern unsigned long __start_likely_profile[];
 283 extern unsigned long __stop_likely_profile[];
 284 extern unsigned long __start_unlikely_profile[];
 285 extern unsigned long __stop_unlikely_profile[];
 286
 287 static struct ftrace_pointer ftrace_likely_pos = {
 288         .start                  = __start_likely_profile,
 289         .stop                   = __stop_likely_profile,
 290 };
 291
 292 static struct ftrace_pointer ftrace_unlikely_pos = {
 293         .start                  = __start_unlikely_profile,
 294         .stop                   = __stop_unlikely_profile,
 295 };
 296
 297 static __init int ftrace_branch_init(void)
 298 {
 299         struct dentry *d_tracer;
 300         struct dentry *entry;
 301
 302         d_tracer = tracing_init_dentry();
 303
 304         entry = debugfs_create_file("profile_likely", 0444, d_tracer,
 305                                     &ftrace_likely_pos,
 306                                     &tracing_likely_fops);
 307         if (!entry)
 308                 pr_warning("Could not create debugfs 'profile_likely' entry\n");
 309
 310         entry = debugfs_create_file("profile_unlikely", 0444, d_tracer,
 311                                     &ftrace_unlikely_pos,
 312                                     &tracing_likely_fops);
 313         if (!entry)
 314                 pr_warning("Could not create debugfs"
 315                            " 'profile_unlikely' entry\n");
 316
 317         return 0;
 318 }
 319
 320 device_initcall(ftrace_branch_init);