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Diffstat (limited to 'libgo/go/runtime/cpuprof.go')
| -rw-r--r-- | libgo/go/runtime/cpuprof.go | 454 |
1 files changed, 454 insertions, 0 deletions
diff --git a/libgo/go/runtime/cpuprof.go b/libgo/go/runtime/cpuprof.go new file mode 100644 index 0000000000..e1206f99f1 --- /dev/null +++ b/libgo/go/runtime/cpuprof.go @@ -0,0 +1,454 @@ +// Copyright 2011 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +// CPU profiling. +// Based on algorithms and data structures used in +// https://github.com/google/pprof. +// +// The main difference between this code and the google-perftools +// code is that this code is written to allow copying the profile data +// to an arbitrary io.Writer, while the google-perftools code always +// writes to an operating system file. +// +// The signal handler for the profiling clock tick adds a new stack trace +// to a hash table tracking counts for recent traces. Most clock ticks +// hit in the cache. In the event of a cache miss, an entry must be +// evicted from the hash table, copied to a log that will eventually be +// written as profile data. The google-perftools code flushed the +// log itself during the signal handler. This code cannot do that, because +// the io.Writer might block or need system calls or locks that are not +// safe to use from within the signal handler. Instead, we split the log +// into two halves and let the signal handler fill one half while a goroutine +// is writing out the other half. When the signal handler fills its half, it +// offers to swap with the goroutine. If the writer is not done with its half, +// we lose the stack trace for this clock tick (and record that loss). +// The goroutine interacts with the signal handler by calling getprofile() to +// get the next log piece to write, implicitly handing back the last log +// piece it obtained. +// +// The state of this dance between the signal handler and the goroutine +// is encoded in the Profile.handoff field. If handoff == 0, then the goroutine +// is not using either log half and is waiting (or will soon be waiting) for +// a new piece by calling notesleep(&p.wait). If the signal handler +// changes handoff from 0 to non-zero, it must call notewakeup(&p.wait) +// to wake the goroutine. The value indicates the number of entries in the +// log half being handed off. The goroutine leaves the non-zero value in +// place until it has finished processing the log half and then flips the number +// back to zero. Setting the high bit in handoff means that the profiling is over, +// and the goroutine is now in charge of flushing the data left in the hash table +// to the log and returning that data. +// +// The handoff field is manipulated using atomic operations. +// For the most part, the manipulation of handoff is orderly: if handoff == 0 +// then the signal handler owns it and can change it to non-zero. +// If handoff != 0 then the goroutine owns it and can change it to zero. +// If that were the end of the story then we would not need to manipulate +// handoff using atomic operations. The operations are needed, however, +// in order to let the log closer set the high bit to indicate "EOF" safely +// in the situation when normally the goroutine "owns" handoff. + +package runtime + +import ( + "runtime/internal/atomic" + "unsafe" +) + +const ( + numBuckets = 1 << 10 + logSize = 1 << 17 + assoc = 4 + maxCPUProfStack = 64 +) + +type cpuprofEntry struct { + count uintptr + depth int + stack [maxCPUProfStack]uintptr +} + +//go:notinheap +type cpuProfile struct { + on bool // profiling is on + wait note // goroutine waits here + count uintptr // tick count + evicts uintptr // eviction count + lost uintptr // lost ticks that need to be logged + + // Active recent stack traces. + hash [numBuckets]struct { + entry [assoc]cpuprofEntry + } + + // Log of traces evicted from hash. + // Signal handler has filled log[toggle][:nlog]. + // Goroutine is writing log[1-toggle][:handoff]. + log [2][logSize / 2]uintptr + nlog int + toggle int32 + handoff uint32 + + // Writer state. + // Writer maintains its own toggle to avoid races + // looking at signal handler's toggle. + wtoggle uint32 + wholding bool // holding & need to release a log half + flushing bool // flushing hash table - profile is over + eodSent bool // special end-of-data record sent; => flushing +} + +var ( + cpuprofLock mutex + cpuprof *cpuProfile + + eod = [3]uintptr{0, 1, 0} +) + +func setcpuprofilerate(hz int32) { + systemstack(func() { + setcpuprofilerate_m(hz) + }) +} + +// lostProfileData is a no-op function used in profiles +// to mark the number of profiling stack traces that were +// discarded due to slow data writers. +func lostProfileData() {} + +// SetCPUProfileRate sets the CPU profiling rate to hz samples per second. +// If hz <= 0, SetCPUProfileRate turns off profiling. +// If the profiler is on, the rate cannot be changed without first turning it off. +// +// Most clients should use the runtime/pprof package or +// the testing package's -test.cpuprofile flag instead of calling +// SetCPUProfileRate directly. +func SetCPUProfileRate(hz int) { + // Clamp hz to something reasonable. + if hz < 0 { + hz = 0 + } + if hz > 1000000 { + hz = 1000000 + } + + lock(&cpuprofLock) + if hz > 0 { + if cpuprof == nil { + cpuprof = (*cpuProfile)(sysAlloc(unsafe.Sizeof(cpuProfile{}), &memstats.other_sys)) + if cpuprof == nil { + print("runtime: cpu profiling cannot allocate memory\n") + unlock(&cpuprofLock) + return + } + } + if cpuprof.on || cpuprof.handoff != 0 { + print("runtime: cannot set cpu profile rate until previous profile has finished.\n") + unlock(&cpuprofLock) + return + } + + cpuprof.on = true + // pprof binary header format. + // https://github.com/gperftools/gperftools/blob/master/src/profiledata.cc#L119 + p := &cpuprof.log[0] + p[0] = 0 // count for header + p[1] = 3 // depth for header + p[2] = 0 // version number + p[3] = uintptr(1e6 / hz) // period (microseconds) + p[4] = 0 + cpuprof.nlog = 5 + cpuprof.toggle = 0 + cpuprof.wholding = false + cpuprof.wtoggle = 0 + cpuprof.flushing = false + cpuprof.eodSent = false + noteclear(&cpuprof.wait) + + setcpuprofilerate(int32(hz)) + } else if cpuprof != nil && cpuprof.on { + setcpuprofilerate(0) + cpuprof.on = false + + // Now add is not running anymore, and getprofile owns the entire log. + // Set the high bit in cpuprof.handoff to tell getprofile. + for { + n := cpuprof.handoff + if n&0x80000000 != 0 { + print("runtime: setcpuprofile(off) twice\n") + } + if atomic.Cas(&cpuprof.handoff, n, n|0x80000000) { + if n == 0 { + // we did the transition from 0 -> nonzero so we wake getprofile + notewakeup(&cpuprof.wait) + } + break + } + } + } + unlock(&cpuprofLock) +} + +// add adds the stack trace to the profile. +// It is called from signal handlers and other limited environments +// and cannot allocate memory or acquire locks that might be +// held at the time of the signal, nor can it use substantial amounts +// of stack. It is allowed to call evict. +//go:nowritebarrierrec +func (p *cpuProfile) add(pc []uintptr) { + p.addWithFlushlog(pc, p.flushlog) +} + +// addWithFlushlog implements add and addNonGo. +// It is called from signal handlers and other limited environments +// and cannot allocate memory or acquire locks that might be +// held at the time of the signal, nor can it use substantial amounts +// of stack. It may be called by a signal handler with no g or m. +// It is allowed to call evict, passing the flushlog parameter. +//go:nosplit +//go:nowritebarrierrec +func (p *cpuProfile) addWithFlushlog(pc []uintptr, flushlog func() bool) { + if len(pc) > maxCPUProfStack { + pc = pc[:maxCPUProfStack] + } + + // Compute hash. + h := uintptr(0) + for _, x := range pc { + h = h<<8 | (h >> (8 * (unsafe.Sizeof(h) - 1))) + h += x * 41 + } + p.count++ + + // Add to entry count if already present in table. + b := &p.hash[h%numBuckets] +Assoc: + for i := range b.entry { + e := &b.entry[i] + if e.depth != len(pc) { + continue + } + for j := range pc { + if e.stack[j] != pc[j] { + continue Assoc + } + } + e.count++ + return + } + + // Evict entry with smallest count. + var e *cpuprofEntry + for i := range b.entry { + if e == nil || b.entry[i].count < e.count { + e = &b.entry[i] + } + } + if e.count > 0 { + if !p.evict(e, flushlog) { + // Could not evict entry. Record lost stack. + p.lost++ + return + } + p.evicts++ + } + + // Reuse the newly evicted entry. + e.depth = len(pc) + e.count = 1 + copy(e.stack[:], pc) +} + +// evict copies the given entry's data into the log, so that +// the entry can be reused. evict is called from add, which +// is called from the profiling signal handler, so it must not +// allocate memory or block, and it may be called with no g or m. +// It is safe to call flushlog. evict returns true if the entry was +// copied to the log, false if there was no room available. +//go:nosplit +//go:nowritebarrierrec +func (p *cpuProfile) evict(e *cpuprofEntry, flushlog func() bool) bool { + d := e.depth + nslot := d + 2 + log := &p.log[p.toggle] + if p.nlog+nslot > len(log) { + if !flushlog() { + return false + } + log = &p.log[p.toggle] + } + + q := p.nlog + log[q] = e.count + q++ + log[q] = uintptr(d) + q++ + copy(log[q:], e.stack[:d]) + q += d + p.nlog = q + e.count = 0 + return true +} + +// flushlog tries to flush the current log and switch to the other one. +// flushlog is called from evict, called from add, called from the signal handler, +// so it cannot allocate memory or block. It can try to swap logs with +// the writing goroutine, as explained in the comment at the top of this file. +//go:nowritebarrierrec +func (p *cpuProfile) flushlog() bool { + if !atomic.Cas(&p.handoff, 0, uint32(p.nlog)) { + return false + } + notewakeup(&p.wait) + + p.toggle = 1 - p.toggle + log := &p.log[p.toggle] + q := 0 + if p.lost > 0 { + lostPC := funcPC(lostProfileData) + log[0] = p.lost + log[1] = 1 + log[2] = lostPC + q = 3 + p.lost = 0 + } + p.nlog = q + return true +} + +// addNonGo is like add, but runs on a non-Go thread. +// It can't do anything that might need a g or an m. +// With this entry point, we don't try to flush the log when evicting an +// old entry. Instead, we just drop the stack trace if we're out of space. +//go:nosplit +//go:nowritebarrierrec +func (p *cpuProfile) addNonGo(pc []uintptr) { + p.addWithFlushlog(pc, func() bool { return false }) +} + +// getprofile blocks until the next block of profiling data is available +// and returns it as a []byte. It is called from the writing goroutine. +func (p *cpuProfile) getprofile() []byte { + if p == nil { + return nil + } + + if p.wholding { + // Release previous log to signal handling side. + // Loop because we are racing against SetCPUProfileRate(0). + for { + n := p.handoff + if n == 0 { + print("runtime: phase error during cpu profile handoff\n") + return nil + } + if n&0x80000000 != 0 { + p.wtoggle = 1 - p.wtoggle + p.wholding = false + p.flushing = true + goto Flush + } + if atomic.Cas(&p.handoff, n, 0) { + break + } + } + p.wtoggle = 1 - p.wtoggle + p.wholding = false + } + + if p.flushing { + goto Flush + } + + if !p.on && p.handoff == 0 { + return nil + } + + // Wait for new log. + notetsleepg(&p.wait, -1) + noteclear(&p.wait) + + switch n := p.handoff; { + case n == 0: + print("runtime: phase error during cpu profile wait\n") + return nil + case n == 0x80000000: + p.flushing = true + goto Flush + default: + n &^= 0x80000000 + + // Return new log to caller. + p.wholding = true + + return uintptrBytes(p.log[p.wtoggle][:n]) + } + + // In flush mode. + // Add is no longer being called. We own the log. + // Also, p.handoff is non-zero, so flushlog will return false. + // Evict the hash table into the log and return it. +Flush: + for i := range p.hash { + b := &p.hash[i] + for j := range b.entry { + e := &b.entry[j] + if e.count > 0 && !p.evict(e, p.flushlog) { + // Filled the log. Stop the loop and return what we've got. + break Flush + } + } + } + + // Return pending log data. + if p.nlog > 0 { + // Note that we're using toggle now, not wtoggle, + // because we're working on the log directly. + n := p.nlog + p.nlog = 0 + return uintptrBytes(p.log[p.toggle][:n]) + } + + // Made it through the table without finding anything to log. + if !p.eodSent { + // We may not have space to append this to the partial log buf, + // so we always return a new slice for the end-of-data marker. + p.eodSent = true + return uintptrBytes(eod[:]) + } + + // Finally done. Clean up and return nil. + p.flushing = false + if !atomic.Cas(&p.handoff, p.handoff, 0) { + print("runtime: profile flush racing with something\n") + } + return nil +} + +func uintptrBytes(p []uintptr) (ret []byte) { + pp := (*slice)(unsafe.Pointer(&p)) + rp := (*slice)(unsafe.Pointer(&ret)) + + rp.array = pp.array + rp.len = pp.len * int(unsafe.Sizeof(p[0])) + rp.cap = rp.len + + return +} + +// CPUProfile returns the next chunk of binary CPU profiling stack trace data, +// blocking until data is available. If profiling is turned off and all the profile +// data accumulated while it was on has been returned, CPUProfile returns nil. +// The caller must save the returned data before calling CPUProfile again. +// +// Most clients should use the runtime/pprof package or +// the testing package's -test.cpuprofile flag instead of calling +// CPUProfile directly. +func CPUProfile() []byte { + return cpuprof.getprofile() +} + +//go:linkname runtime_pprof_runtime_cyclesPerSecond runtime_pprof.runtime_cyclesPerSecond +func runtime_pprof_runtime_cyclesPerSecond() int64 { + return tickspersecond() +} |