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Source file src/runtime/cpuprof.go

Documentation: runtime

     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  }
    43  
    44  var cpuprof cpuProfile
    45  
    46  // SetCPUProfileRate sets the CPU profiling rate to hz samples per second.
    47  // If hz <= 0, SetCPUProfileRate turns off profiling.
    48  // If the profiler is on, the rate cannot be changed without first turning it off.
    49  //
    50  // Most clients should use the runtime/pprof package or
    51  // the testing package's -test.cpuprofile flag instead of calling
    52  // SetCPUProfileRate directly.
    53  func SetCPUProfileRate(hz int) {
    54  	// Clamp hz to something reasonable.
    55  	if hz < 0 {
    56  		hz = 0
    57  	}
    58  	if hz > 1000000 {
    59  		hz = 1000000
    60  	}
    61  
    62  	lock(&cpuprof.lock)
    63  	if hz > 0 {
    64  		if cpuprof.on || cpuprof.log != nil {
    65  			print("runtime: cannot set cpu profile rate until previous profile has finished.\n")
    66  			unlock(&cpuprof.lock)
    67  			return
    68  		}
    69  
    70  		cpuprof.on = true
    71  		cpuprof.log = newProfBuf(1, 1<<17, 1<<14)
    72  		hdr := [1]uint64{uint64(hz)}
    73  		cpuprof.log.write(nil, nanotime(), hdr[:], nil)
    74  		setcpuprofilerate(int32(hz))
    75  	} else if cpuprof.on {
    76  		setcpuprofilerate(0)
    77  		cpuprof.on = false
    78  		cpuprof.addExtra()
    79  		cpuprof.log.close()
    80  	}
    81  	unlock(&cpuprof.lock)
    82  }
    83  
    84  // add adds the stack trace to the profile.
    85  // It is called from signal handlers and other limited environments
    86  // and cannot allocate memory or acquire locks that might be
    87  // held at the time of the signal, nor can it use substantial amounts
    88  // of stack.
    89  //go:nowritebarrierrec
    90  func (p *cpuProfile) add(gp *g, stk []uintptr) {
    91  	// Simple cas-lock to coordinate with setcpuprofilerate.
    92  	for !atomic.Cas(&prof.signalLock, 0, 1) {
    93  		osyield()
    94  	}
    95  
    96  	if prof.hz != 0 { // implies cpuprof.log != nil
    97  		if p.numExtra > 0 || p.lostExtra > 0 {
    98  			p.addExtra()
    99  		}
   100  		hdr := [1]uint64{1}
   101  		// Note: write "knows" that the argument is &gp.labels,
   102  		// because otherwise its write barrier behavior may not
   103  		// be correct. See the long comment there before
   104  		// changing the argument here.
   105  		cpuprof.log.write(&gp.labels, nanotime(), hdr[:], stk)
   106  	}
   107  
   108  	atomic.Store(&prof.signalLock, 0)
   109  }
   110  
   111  // addNonGo adds the non-Go stack trace to the profile.
   112  // It is called from a non-Go thread, so we cannot use much stack at all,
   113  // nor do anything that needs a g or an m.
   114  // In particular, we can't call cpuprof.log.write.
   115  // Instead, we copy the stack into cpuprof.extra,
   116  // which will be drained the next time a Go thread
   117  // gets the signal handling event.
   118  //go:nosplit
   119  //go:nowritebarrierrec
   120  func (p *cpuProfile) addNonGo(stk []uintptr) {
   121  	// Simple cas-lock to coordinate with SetCPUProfileRate.
   122  	// (Other calls to add or addNonGo should be blocked out
   123  	// by the fact that only one SIGPROF can be handled by the
   124  	// process at a time. If not, this lock will serialize those too.)
   125  	for !atomic.Cas(&prof.signalLock, 0, 1) {
   126  		osyield()
   127  	}
   128  
   129  	if cpuprof.numExtra+1+len(stk) < len(cpuprof.extra) {
   130  		i := cpuprof.numExtra
   131  		cpuprof.extra[i] = uintptr(1 + len(stk))
   132  		copy(cpuprof.extra[i+1:], stk)
   133  		cpuprof.numExtra += 1 + len(stk)
   134  	} else {
   135  		cpuprof.lostExtra++
   136  	}
   137  
   138  	atomic.Store(&prof.signalLock, 0)
   139  }
   140  
   141  // addExtra adds the "extra" profiling events,
   142  // queued by addNonGo, to the profile log.
   143  // addExtra is called either from a signal handler on a Go thread
   144  // or from an ordinary goroutine; either way it can use stack
   145  // and has a g. The world may be stopped, though.
   146  func (p *cpuProfile) addExtra() {
   147  	// Copy accumulated non-Go profile events.
   148  	hdr := [1]uint64{1}
   149  	for i := 0; i < p.numExtra; {
   150  		p.log.write(nil, 0, hdr[:], p.extra[i+1:i+int(p.extra[i])])
   151  		i += int(p.extra[i])
   152  	}
   153  	p.numExtra = 0
   154  
   155  	// Report any lost events.
   156  	if p.lostExtra > 0 {
   157  		hdr := [1]uint64{p.lostExtra}
   158  		lostStk := [2]uintptr{
   159  			funcPC(_LostExternalCode) + sys.PCQuantum,
   160  			funcPC(_ExternalCode) + sys.PCQuantum,
   161  		}
   162  		cpuprof.log.write(nil, 0, hdr[:], lostStk[:])
   163  		p.lostExtra = 0
   164  	}
   165  }
   166  
   167  func (p *cpuProfile) addLostAtomic64(count uint64) {
   168  	hdr := [1]uint64{count}
   169  	lostStk := [2]uintptr{
   170  		funcPC(_LostSIGPROFDuringAtomic64) + sys.PCQuantum,
   171  		funcPC(_System) + sys.PCQuantum,
   172  	}
   173  	cpuprof.log.write(nil, 0, hdr[:], lostStk[:])
   174  }
   175  
   176  // CPUProfile panics.
   177  // It formerly provided raw access to chunks of
   178  // a pprof-format profile generated by the runtime.
   179  // The details of generating that format have changed,
   180  // so this functionality has been removed.
   181  //
   182  // Deprecated: use the runtime/pprof package,
   183  // or the handlers in the net/http/pprof package,
   184  // or the testing package's -test.cpuprofile flag instead.
   185  func CPUProfile() []byte {
   186  	panic("CPUProfile no longer available")
   187  }
   188  
   189  //go:linkname runtime_pprof_runtime_cyclesPerSecond runtime/pprof.runtime_cyclesPerSecond
   190  func runtime_pprof_runtime_cyclesPerSecond() int64 {
   191  	return tickspersecond()
   192  }
   193  
   194  // readProfile, provided to runtime/pprof, returns the next chunk of
   195  // binary CPU profiling stack trace data, blocking until data is available.
   196  // If profiling is turned off and all the profile data accumulated while it was
   197  // on has been returned, readProfile returns eof=true.
   198  // The caller must save the returned data and tags before calling readProfile again.
   199  //
   200  //go:linkname runtime_pprof_readProfile runtime/pprof.readProfile
   201  func runtime_pprof_readProfile() ([]uint64, []unsafe.Pointer, bool) {
   202  	lock(&cpuprof.lock)
   203  	log := cpuprof.log
   204  	unlock(&cpuprof.lock)
   205  	data, tags, eof := log.read(profBufBlocking)
   206  	if len(data) == 0 && eof {
   207  		lock(&cpuprof.lock)
   208  		cpuprof.log = nil
   209  		unlock(&cpuprof.lock)
   210  	}
   211  	return data, tags, eof
   212  }
   213  

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