libgo/go/runtime/cpuprof.go

   1 // Copyright 2011 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 // CPU profiling.
   6 //
   7 // The signal handler for the profiling clock tick adds a new stack trace
   8 // to a log of recent traces. The log is read by a user goroutine that
   9 // turns it into formatted profile data. If the reader does not keep up
  10 // with the log, those writes will be recorded as a count of lost records.
  11 // The actual profile buffer is in profbuf.go.
  12
  13 package runtime
  14
  15 import (
  16         "runtime/internal/atomic"
  17         "runtime/internal/sys"
  18         "unsafe"
  19 )
  20
  21 const maxCPUProfStack = 64
  22
  23 type cpuProfile struct {
  24         lock mutex
  25         on   bool     // profiling is on
  26         log  *profBuf // profile events written here
  27
  28         // extra holds extra stacks accumulated in addNonGo
  29         // corresponding to profiling signals arriving on
  30         // non-Go-created threads. Those stacks are written
  31         // to log the next time a normal Go thread gets the
  32         // signal handler.
  33         // Assuming the stacks are 2 words each (we don't get
  34         // a full traceback from those threads), plus one word
  35         // size for framing, 100 Hz profiling would generate
  36         // 300 words per second.
  37         // Hopefully a normal Go thread will get the profiling
  38         // signal at least once every few seconds.
  39         extra      [1000]uintptr
  40         numExtra   int
  41         lostExtra  uint64 // count of frames lost because extra is full
  42         lostAtomic uint64 // count of frames lost because of being in atomic64 on mips/arm; updated racily
  43 }
  44
  45 var cpuprof cpuProfile
  46
  47 // SetCPUProfileRate sets the CPU profiling rate to hz samples per second.
  48 // If hz <= 0, SetCPUProfileRate turns off profiling.
  49 // If the profiler is on, the rate cannot be changed without first turning it off.
  50 //
  51 // Most clients should use the runtime/pprof package or
  52 // the testing package's -test.cpuprofile flag instead of calling
  53 // SetCPUProfileRate directly.
  54 func SetCPUProfileRate(hz int) {
  55         // Clamp hz to something reasonable.
  56         if hz < 0 {
  57                 hz = 0
  58         }
  59         if hz > 1000000 {
  60                 hz = 1000000
  61         }
  62
  63         lock(&cpuprof.lock)
  64         if hz > 0 {
  65                 if cpuprof.on || cpuprof.log != nil {
  66                         print("runtime: cannot set cpu profile rate until previous profile has finished.\n")
  67                         unlock(&cpuprof.lock)
  68                         return
  69                 }
  70
  71                 cpuprof.on = true
  72                 cpuprof.log = newProfBuf(1, 1<<17, 1<<14)
  73                 hdr := [1]uint64{uint64(hz)}
  74                 cpuprof.log.write(nil, nanotime(), hdr[:], nil)
  75                 setcpuprofilerate(int32(hz))
  76         } else if cpuprof.on {
  77                 setcpuprofilerate(0)
  78                 cpuprof.on = false
  79                 cpuprof.addExtra()
  80                 cpuprof.log.close()
  81         }
  82         unlock(&cpuprof.lock)
  83 }
  84
  85 // add adds the stack trace to the profile.
  86 // It is called from signal handlers and other limited environments
  87 // and cannot allocate memory or acquire locks that might be
  88 // held at the time of the signal, nor can it use substantial amounts
  89 // of stack.
  90 //go:nowritebarrierrec
  91 func (p *cpuProfile) add(gp *g, stk []uintptr) {
  92         // Simple cas-lock to coordinate with setcpuprofilerate.
  93         for !atomic.Cas(&prof.signalLock, 0, 1) {
  94                 osyield()
  95         }
  96
  97         if prof.hz != 0 { // implies cpuprof.log != nil
  98                 if p.numExtra > 0 || p.lostExtra > 0 || p.lostAtomic > 0 {
  99                         p.addExtra()
 100                 }
 101                 hdr := [1]uint64{1}
 102                 // Note: write "knows" that the argument is &gp.labels,
 103                 // because otherwise its write barrier behavior may not
 104                 // be correct. See the long comment there before
 105                 // changing the argument here.
 106                 cpuprof.log.write(&gp.labels, nanotime(), hdr[:], stk)
 107         }
 108
 109         atomic.Store(&prof.signalLock, 0)
 110 }
 111
 112 // addNonGo adds the non-Go stack trace to the profile.
 113 // It is called from a non-Go thread, so we cannot use much stack at all,
 114 // nor do anything that needs a g or an m.
 115 // In particular, we can't call cpuprof.log.write.
 116 // Instead, we copy the stack into cpuprof.extra,
 117 // which will be drained the next time a Go thread
 118 // gets the signal handling event.
 119 //go:nosplit
 120 //go:nowritebarrierrec
 121 func (p *cpuProfile) addNonGo(stk []uintptr) {
 122         // Simple cas-lock to coordinate with SetCPUProfileRate.
 123         // (Other calls to add or addNonGo should be blocked out
 124         // by the fact that only one SIGPROF can be handled by the
 125         // process at a time. If not, this lock will serialize those too.)
 126         for !atomic.Cas(&prof.signalLock, 0, 1) {
 127                 osyield()
 128         }
 129
 130         if cpuprof.numExtra+1+len(stk) < len(cpuprof.extra) {
 131                 i := cpuprof.numExtra
 132                 cpuprof.extra[i] = uintptr(1 + len(stk))
 133                 copy(cpuprof.extra[i+1:], stk)
 134                 cpuprof.numExtra += 1 + len(stk)
 135         } else {
 136                 cpuprof.lostExtra++
 137         }
 138
 139         atomic.Store(&prof.signalLock, 0)
 140 }
 141
 142 // addExtra adds the "extra" profiling events,
 143 // queued by addNonGo, to the profile log.
 144 // addExtra is called either from a signal handler on a Go thread
 145 // or from an ordinary goroutine; either way it can use stack
 146 // and has a g. The world may be stopped, though.
 147 func (p *cpuProfile) addExtra() {
 148         // Copy accumulated non-Go profile events.
 149         hdr := [1]uint64{1}
 150         for i := 0; i < p.numExtra; {
 151                 p.log.write(nil, 0, hdr[:], p.extra[i+1:i+int(p.extra[i])])
 152                 i += int(p.extra[i])
 153         }
 154         p.numExtra = 0
 155
 156         // Report any lost events.
 157         if p.lostExtra > 0 {
 158                 hdr := [1]uint64{p.lostExtra}
 159                 lostStk := [2]uintptr{
 160                         _LostExternalCodePC + sys.PCQuantum,
 161                         _ExternalCodePC + sys.PCQuantum,
 162                 }
 163                 p.log.write(nil, 0, hdr[:], lostStk[:])
 164                 p.lostExtra = 0
 165         }
 166
 167         if p.lostAtomic > 0 {
 168                 hdr := [1]uint64{p.lostAtomic}
 169                 lostStk := [2]uintptr{
 170                         _LostSIGPROFDuringAtomic64PC + sys.PCQuantum,
 171                         _SystemPC + sys.PCQuantum,
 172                 }
 173                 p.log.write(nil, 0, hdr[:], lostStk[:])
 174                 p.lostAtomic = 0
 175         }
 176
 177 }
 178
 179 // CPUProfile panics.
 180 // It formerly provided raw access to chunks of
 181 // a pprof-format profile generated by the runtime.
 182 // The details of generating that format have changed,
 183 // so this functionality has been removed.
 184 //
 185 // Deprecated: Use the runtime/pprof package,
 186 // or the handlers in the net/http/pprof package,
 187 // or the testing package's -test.cpuprofile flag instead.
 188 func CPUProfile() []byte {
 189         panic("CPUProfile no longer available")
 190 }
 191
 192 //go:linkname runtime_pprof_runtime_cyclesPerSecond runtime..z2fpprof.runtime_cyclesPerSecond
 193 func runtime_pprof_runtime_cyclesPerSecond() int64 {
 194         return tickspersecond()
 195 }
 196
 197 // readProfile, provided to runtime/pprof, returns the next chunk of
 198 // binary CPU profiling stack trace data, blocking until data is available.
 199 // If profiling is turned off and all the profile data accumulated while it was
 200 // on has been returned, readProfile returns eof=true.
 201 // The caller must save the returned data and tags before calling readProfile again.
 202 //
 203 //go:linkname runtime_pprof_readProfile runtime..z2fpprof.readProfile
 204 func runtime_pprof_readProfile() ([]uint64, []unsafe.Pointer, bool) {
 205         lock(&cpuprof.lock)
 206         log := cpuprof.log
 207         unlock(&cpuprof.lock)
 208         data, tags, eof := log.read(profBufBlocking)
 209         if len(data) == 0 && eof {
 210                 lock(&cpuprof.lock)
 211                 cpuprof.log = nil
 212                 unlock(&cpuprof.lock)
 213         }
 214         return data, tags, eof
 215 }