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.
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.
17 "runtime/internal/sys"
24 // profBufWordCount is the size of the CPU profile buffer's storage for the
25 // header and stack of each sample, measured in 64-bit words. Every sample
26 // has a required header of two words. With a small additional header (a
27 // word or two) and stacks at the profiler's maximum length of 64 frames,
28 // that capacity can support 1900 samples or 19 thread-seconds at a 100 Hz
29 // sample rate, at a cost of 1 MiB.
30 profBufWordCount = 1 << 17
31 // profBufTagCount is the size of the CPU profile buffer's storage for the
32 // goroutine tags associated with each sample. A capacity of 1<<14 means
33 // room for 16k samples, or 160 thread-seconds at a 100 Hz sample rate.
34 profBufTagCount = 1 << 14
37 type cpuProfile struct {
39 on bool // profiling is on
40 log *profBuf // profile events written here
42 // extra holds extra stacks accumulated in addNonGo
43 // corresponding to profiling signals arriving on
44 // non-Go-created threads. Those stacks are written
45 // to log the next time a normal Go thread gets the
47 // Assuming the stacks are 2 words each (we don't get
48 // a full traceback from those threads), plus one word
49 // size for framing, 100 Hz profiling would generate
50 // 300 words per second.
51 // Hopefully a normal Go thread will get the profiling
52 // signal at least once every few seconds.
55 lostExtra uint64 // count of frames lost because extra is full
56 lostAtomic uint64 // count of frames lost because of being in atomic64 on mips/arm; updated racily
59 var cpuprof cpuProfile
61 // SetCPUProfileRate sets the CPU profiling rate to hz samples per second.
62 // If hz <= 0, SetCPUProfileRate turns off profiling.
63 // If the profiler is on, the rate cannot be changed without first turning it off.
65 // Most clients should use the runtime/pprof package or
66 // the testing package's -test.cpuprofile flag instead of calling
67 // SetCPUProfileRate directly.
68 func SetCPUProfileRate(hz int) {
69 // Clamp hz to something reasonable.
79 if cpuprof.on || cpuprof.log != nil {
80 print("runtime: cannot set cpu profile rate until previous profile has finished.\n")
86 cpuprof.log = newProfBuf(1, profBufWordCount, profBufTagCount)
87 hdr := [1]uint64{uint64(hz)}
88 cpuprof.log.write(nil, nanotime(), hdr[:], nil)
89 setcpuprofilerate(int32(hz))
90 } else if cpuprof.on {
99 // add adds the stack trace to the profile.
100 // It is called from signal handlers and other limited environments
101 // and cannot allocate memory or acquire locks that might be
102 // held at the time of the signal, nor can it use substantial amounts
105 //go:nowritebarrierrec
106 func (p *cpuProfile) add(tagPtr *unsafe.Pointer, stk []uintptr) {
107 // Simple cas-lock to coordinate with setcpuprofilerate.
108 for !prof.signalLock.CompareAndSwap(0, 1) {
109 // TODO: Is it safe to osyield here? https://go.dev/issue/52672
113 if prof.hz.Load() != 0 { // implies cpuprof.log != nil
114 if p.numExtra > 0 || p.lostExtra > 0 || p.lostAtomic > 0 {
118 // Note: write "knows" that the argument is &gp.labels,
119 // because otherwise its write barrier behavior may not
120 // be correct. See the long comment there before
121 // changing the argument here.
122 cpuprof.log.write(tagPtr, nanotime(), hdr[:], stk)
125 prof.signalLock.Store(0)
128 // addNonGo adds the non-Go stack trace to the profile.
129 // It is called from a non-Go thread, so we cannot use much stack at all,
130 // nor do anything that needs a g or an m.
131 // In particular, we can't call cpuprof.log.write.
132 // Instead, we copy the stack into cpuprof.extra,
133 // which will be drained the next time a Go thread
134 // gets the signal handling event.
137 //go:nowritebarrierrec
138 func (p *cpuProfile) addNonGo(stk []uintptr) {
139 // Simple cas-lock to coordinate with SetCPUProfileRate.
140 // (Other calls to add or addNonGo should be blocked out
141 // by the fact that only one SIGPROF can be handled by the
142 // process at a time. If not, this lock will serialize those too.
143 // The use of timer_create(2) on Linux to request process-targeted
144 // signals may have changed this.)
145 for !prof.signalLock.CompareAndSwap(0, 1) {
146 // TODO: Is it safe to osyield here? https://go.dev/issue/52672
150 if cpuprof.numExtra+1+len(stk) < len(cpuprof.extra) {
151 i := cpuprof.numExtra
152 cpuprof.extra[i] = uintptr(1 + len(stk))
153 copy(cpuprof.extra[i+1:], stk)
154 cpuprof.numExtra += 1 + len(stk)
159 prof.signalLock.Store(0)
162 // addExtra adds the "extra" profiling events,
163 // queued by addNonGo, to the profile log.
164 // addExtra is called either from a signal handler on a Go thread
165 // or from an ordinary goroutine; either way it can use stack
166 // and has a g. The world may be stopped, though.
167 func (p *cpuProfile) addExtra() {
168 // Copy accumulated non-Go profile events.
170 for i := 0; i < p.numExtra; {
171 p.log.write(nil, 0, hdr[:], p.extra[i+1:i+int(p.extra[i])])
176 // Report any lost events.
178 hdr := [1]uint64{p.lostExtra}
179 lostStk := [2]uintptr{
180 abi.FuncPCABIInternal(_LostExternalCode) + sys.PCQuantum,
181 abi.FuncPCABIInternal(_ExternalCode) + sys.PCQuantum,
183 p.log.write(nil, 0, hdr[:], lostStk[:])
187 if p.lostAtomic > 0 {
188 hdr := [1]uint64{p.lostAtomic}
189 lostStk := [2]uintptr{
190 abi.FuncPCABIInternal(_LostSIGPROFDuringAtomic64) + sys.PCQuantum,
191 abi.FuncPCABIInternal(_System) + sys.PCQuantum,
193 p.log.write(nil, 0, hdr[:], lostStk[:])
199 // CPUProfile panics.
200 // It formerly provided raw access to chunks of
201 // a pprof-format profile generated by the runtime.
202 // The details of generating that format have changed,
203 // so this functionality has been removed.
205 // Deprecated: Use the runtime/pprof package,
206 // or the handlers in the net/http/pprof package,
207 // or the testing package's -test.cpuprofile flag instead.
208 func CPUProfile() []byte {
209 panic("CPUProfile no longer available")
212 //go:linkname runtime_pprof_runtime_cyclesPerSecond runtime/pprof.runtime_cyclesPerSecond
213 func runtime_pprof_runtime_cyclesPerSecond() int64 {
214 return tickspersecond()
217 // readProfile, provided to runtime/pprof, returns the next chunk of
218 // binary CPU profiling stack trace data, blocking until data is available.
219 // If profiling is turned off and all the profile data accumulated while it was
220 // on has been returned, readProfile returns eof=true.
221 // The caller must save the returned data and tags before calling readProfile again.
222 // The returned data contains a whole number of records, and tags contains
223 // exactly one entry per record.
225 //go:linkname runtime_pprof_readProfile runtime/pprof.readProfile
226 func runtime_pprof_readProfile() ([]uint64, []unsafe.Pointer, bool) {
229 unlock(&cpuprof.lock)
230 readMode := profBufBlocking
231 if GOOS == "darwin" || GOOS == "ios" {
232 readMode = profBufNonBlocking // For #61768; on Darwin notes are not async-signal-safe. See sigNoteSetup in os_darwin.go.
234 data, tags, eof := log.read(readMode)
235 if len(data) == 0 && eof {
238 unlock(&cpuprof.lock)
240 return data, tags, eof