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authorRuss Cox <rsc@golang.org>2014-09-08 00:08:51 -0400
committerRuss Cox <rsc@golang.org>2014-09-08 00:08:51 -0400
commitc007ce824d9a4fccb148f9204e04c23ed2984b71 (patch)
tree7dcac257114ef5c446be5b7b68c27dea230b7c09 /src/runtime/cpuprof.go
parent220a6de47eced55956eb8af8d643d4f5b67fd634 (diff)
downloadgo-c007ce824d9a4fccb148f9204e04c23ed2984b71.tar.gz
go-c007ce824d9a4fccb148f9204e04c23ed2984b71.zip
build: move package sources from src/pkg to src
Preparation was in CL 134570043. This CL contains only the effect of 'hg mv src/pkg/* src'. For more about the move, see golang.org/s/go14nopkg.
Diffstat (limited to 'src/runtime/cpuprof.go')
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diff --git a/src/runtime/cpuprof.go b/src/runtime/cpuprof.go
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+// 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
+// http://code.google.com/p/google-perftools/.
+//
+// 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 "unsafe"
+
+const (
+ numBuckets = 1 << 10
+ logSize = 1 << 17
+ assoc = 4
+ maxCPUProfStack = 64
+)
+
+type cpuprofEntry struct {
+ count uintptr
+ depth uintptr
+ stack [maxCPUProfStack]uintptr
+}
+
+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 uintptr
+ 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_m() // proc.c
+
+func setcpuprofilerate(hz int32) {
+ g := getg()
+ g.m.scalararg[0] = uintptr(hz)
+ onM(setcpuprofilerate_m)
+}
+
+// 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.
+ // http://code.google.com/p/google-perftools/source/browse/trunk/src/profiledata.cc#117
+ 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 prof->handoff to tell getprofile.
+ for {
+ n := cpuprof.handoff
+ if n&0x80000000 != 0 {
+ print("runtime: setcpuprofile(off) twice\n")
+ }
+ if 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)
+}
+
+func cpuproftick(pc *uintptr, n int32) {
+ if n > maxCPUProfStack {
+ n = maxCPUProfStack
+ }
+ s := (*[maxCPUProfStack]uintptr)(unsafe.Pointer(pc))[:n]
+ cpuprof.add(s)
+}
+
+// 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.
+func (p *cpuProfile) add(pc []uintptr) {
+ // Compute hash.
+ h := uintptr(0)
+ for _, x := range pc {
+ h = h<<8 | (h >> (8 * (unsafe.Sizeof(h) - 1)))
+ h += x*31 + x*7 + x*3
+ }
+ 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 != uintptr(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) {
+ // Could not evict entry. Record lost stack.
+ p.lost++
+ return
+ }
+ p.evicts++
+ }
+
+ // Reuse the newly evicted entry.
+ e.depth = uintptr(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. It is safe to call flushlog.
+// evict returns true if the entry was copied to the log,
+// false if there was no room available.
+func (p *cpuProfile) evict(e *cpuprofEntry) bool {
+ d := e.depth
+ nslot := d + 2
+ log := &p.log[p.toggle]
+ if p.nlog+nslot > uintptr(len(p.log[0])) {
+ if !p.flushlog() {
+ return false
+ }
+ log = &p.log[p.toggle]
+ }
+
+ q := p.nlog
+ log[q] = e.count
+ q++
+ log[q] = 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.
+func (p *cpuProfile) flushlog() bool {
+ if !cas(&p.handoff, 0, uint32(p.nlog)) {
+ return false
+ }
+ notewakeup(&p.wait)
+
+ p.toggle = 1 - p.toggle
+ log := &p.log[p.toggle]
+ q := uintptr(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
+}
+
+// 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 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) {
+ // 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 !cas(&p.handoff, p.handoff, 0) {
+ print("runtime: profile flush racing with something\n")
+ }
+ return nil
+}
+
+func uintptrBytes(p []uintptr) (ret []byte) {
+ pp := (*sliceStruct)(unsafe.Pointer(&p))
+ rp := (*sliceStruct)(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()
+}