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runtime/mem_posix_memalign.c runtime/mem.c runtime/mfinal.c \
runtime/mfixalloc.c runtime/mgc0.c runtime/mheap.c \
runtime/msize.c runtime/proc.c runtime/thread.c \
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--- /dev/null
+// 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.
+
+#include "runtime.h"
+#include "malloc.h"
+
+#include "array.h"
+typedef struct __go_open_array Slice;
+#define array __values
+#define len __count
+#define cap __capacity
+
+enum
+{
+ HashSize = 1<<10,
+ LogSize = 1<<17,
+ Assoc = 4,
+ MaxStack = 64,
+};
+
+typedef struct Profile Profile;
+typedef struct Bucket Bucket;
+typedef struct Entry Entry;
+
+struct Entry {
+ uintptr count;
+ uintptr depth;
+ uintptr stack[MaxStack];
+};
+
+struct Bucket {
+ Entry entry[Assoc];
+};
+
+struct Profile {
+ bool on; // profiling is on
+ Note wait; // goroutine waits here
+ uintptr count; // tick count
+ uintptr evicts; // eviction count
+ uintptr lost; // lost ticks that need to be logged
+ uintptr totallost; // total lost ticks
+
+ // Active recent stack traces.
+ Bucket hash[HashSize];
+
+ // Log of traces evicted from hash.
+ // Signal handler has filled log[toggle][:nlog].
+ // Goroutine is writing log[1-toggle][:handoff].
+ uintptr log[2][LogSize/2];
+ uintptr nlog;
+ int32 toggle;
+ uint32 handoff;
+
+ // Writer state.
+ // Writer maintains its own toggle to avoid races
+ // looking at signal handler's toggle.
+ uint32 wtoggle;
+ bool wholding; // holding & need to release a log half
+ bool flushing; // flushing hash table - profile is over
+};
+
+static Lock lk;
+static Profile *prof;
+
+static void tick(uintptr*, int32);
+static void add(Profile*, uintptr*, int32);
+static bool evict(Profile*, Entry*);
+static bool flushlog(Profile*);
+
+// 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.
+static void LostProfileData(void) {
+}
+
+extern void runtime_SetCPUProfileRate(int32)
+ __asm__("libgo_runtime.runtime.SetCPUProfileRate");
+
+// SetCPUProfileRate sets the CPU profiling rate.
+// The user documentation is in debug.go.
+void
+runtime_SetCPUProfileRate(int32 hz)
+{
+ uintptr *p;
+ uintptr n;
+
+ // Clamp hz to something reasonable.
+ if(hz < 0)
+ hz = 0;
+ if(hz > 1000000)
+ hz = 1000000;
+
+ runtime_lock(&lk);
+ if(hz > 0) {
+ if(prof == nil) {
+ prof = runtime_SysAlloc(sizeof *prof);
+ if(prof == nil) {
+ runtime_printf("runtime: cpu profiling cannot allocate memory\n");
+ runtime_unlock(&lk);
+ return;
+ }
+ }
+ if(prof->on || prof->handoff != 0) {
+ runtime_printf("runtime: cannot set cpu profile rate until previous profile has finished.\n");
+ runtime_unlock(&lk);
+ return;
+ }
+
+ prof->on = true;
+ p = prof->log[0];
+ // pprof binary header format.
+ // http://code.google.com/p/google-perftools/source/browse/trunk/src/profiledata.cc#117
+ *p++ = 0; // count for header
+ *p++ = 3; // depth for header
+ *p++ = 0; // version number
+ *p++ = 1000000 / hz; // period (microseconds)
+ *p++ = 0;
+ prof->nlog = p - prof->log[0];
+ prof->toggle = 0;
+ prof->wholding = false;
+ prof->wtoggle = 0;
+ prof->flushing = false;
+ runtime_noteclear(&prof->wait);
+
+ runtime_setcpuprofilerate(tick, hz);
+ } else if(prof->on) {
+ runtime_setcpuprofilerate(nil, 0);
+ prof->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 = prof->handoff;
+ if(n&0x80000000)
+ runtime_printf("runtime: setcpuprofile(off) twice");
+ if(runtime_cas(&prof->handoff, n, n|0x80000000))
+ break;
+ }
+ if(n == 0) {
+ // we did the transition from 0 -> nonzero so we wake getprofile
+ runtime_notewakeup(&prof->wait);
+ }
+ }
+ runtime_unlock(&lk);
+}
+
+static void
+tick(uintptr *pc, int32 n)
+{
+ add(prof, pc, n);
+}
+
+// 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.
+static void
+add(Profile *p, uintptr *pc, int32 n)
+{
+ int32 i, j;
+ uintptr h, x;
+ Bucket *b;
+ Entry *e;
+
+ if(n > MaxStack)
+ n = MaxStack;
+
+ // Compute hash.
+ h = 0;
+ for(i=0; i<n; i++) {
+ h = h<<8 | (h>>(8*(sizeof(h)-1)));
+ x = pc[i];
+ h += x*31 + x*7 + x*3;
+ }
+ p->count++;
+
+ // Add to entry count if already present in table.
+ b = &p->hash[h%HashSize];
+ for(i=0; i<Assoc; i++) {
+ e = &b->entry[i];
+ if(e->depth != (uintptr)n)
+ continue;
+ for(j=0; j<n; j++)
+ if(e->stack[j] != pc[j])
+ goto ContinueAssoc;
+ e->count++;
+ return;
+ ContinueAssoc:;
+ }
+
+ // Evict entry with smallest count.
+ e = &b->entry[0];
+ for(i=1; i<Assoc; i++)
+ if(b->entry[i].count < e->count)
+ e = &b->entry[i];
+ if(e->count > 0) {
+ if(!evict(p, e)) {
+ // Could not evict entry. Record lost stack.
+ p->lost++;
+ p->totallost++;
+ return;
+ }
+ p->evicts++;
+ }
+
+ // Reuse the newly evicted entry.
+ e->depth = n;
+ e->count = 1;
+ for(i=0; i<n; i++)
+ e->stack[i] = pc[i];
+}
+
+// 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.
+static bool
+evict(Profile *p, Entry *e)
+{
+ int32 i, d, nslot;
+ uintptr *log, *q;
+
+ d = e->depth;
+ nslot = d+2;
+ log = p->log[p->toggle];
+ if(p->nlog+nslot > nelem(p->log[0])) {
+ if(!flushlog(p))
+ return false;
+ log = p->log[p->toggle];
+ }
+
+ q = log+p->nlog;
+ *q++ = e->count;
+ *q++ = d;
+ for(i=0; i<d; i++)
+ *q++ = e->stack[i];
+ p->nlog = q - log;
+ 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.
+static bool
+flushlog(Profile *p)
+{
+ uintptr *log, *q;
+
+ if(!runtime_cas(&p->handoff, 0, p->nlog))
+ return false;
+ runtime_notewakeup(&p->wait);
+
+ p->toggle = 1 - p->toggle;
+ log = p->log[p->toggle];
+ q = log;
+ if(p->lost > 0) {
+ *q++ = p->lost;
+ *q++ = 1;
+ *q++ = (uintptr)LostProfileData;
+ }
+ p->nlog = q - log;
+ 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.
+Slice
+getprofile(Profile *p)
+{
+ uint32 i, j, n;
+ Slice ret;
+ Bucket *b;
+ Entry *e;
+
+ ret.array = nil;
+ ret.len = 0;
+ ret.cap = 0;
+
+ if(p == nil)
+ return ret;
+
+ if(p->wholding) {
+ // Release previous log to signal handling side.
+ // Loop because we are racing against setprofile(off).
+ for(;;) {
+ n = p->handoff;
+ if(n == 0) {
+ runtime_printf("runtime: phase error during cpu profile handoff\n");
+ return ret;
+ }
+ if(n & 0x80000000) {
+ p->wtoggle = 1 - p->wtoggle;
+ p->wholding = false;
+ p->flushing = true;
+ goto flush;
+ }
+ if(runtime_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 ret;
+
+ // Wait for new log.
+ // runtime·entersyscall();
+ runtime_notesleep(&p->wait);
+ // runtime·exitsyscall();
+ runtime_noteclear(&p->wait);
+
+ n = p->handoff;
+ if(n == 0) {
+ runtime_printf("runtime: phase error during cpu profile wait\n");
+ return ret;
+ }
+ if(n == 0x80000000) {
+ p->flushing = true;
+ goto flush;
+ }
+ n &= ~0x80000000;
+
+ // Return new log to caller.
+ p->wholding = true;
+
+ ret.array = (byte*)p->log[p->wtoggle];
+ ret.len = n*sizeof(uintptr);
+ ret.cap = ret.len;
+ return ret;
+
+flush:
+ // 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.
+ for(i=0; i<HashSize; i++) {
+ b = &p->hash[i];
+ for(j=0; j<Assoc; j++) {
+ e = &b->entry[j];
+ if(e->count > 0 && !evict(p, e)) {
+ // Filled the log. Stop the loop and return what we've got.
+ goto breakflush;
+ }
+ }
+ }
+breakflush:
+
+ // 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.
+ ret.array = (byte*)p->log[p->toggle];
+ ret.len = p->nlog*sizeof(uintptr);
+ ret.cap = ret.len;
+ p->nlog = 0;
+ return ret;
+ }
+
+ // Made it through the table without finding anything to log.
+ // Finally done. Clean up and return nil.
+ p->flushing = false;
+ if(!runtime_cas(&p->handoff, p->handoff, 0))
+ runtime_printf("runtime: profile flush racing with something\n");
+ return ret; // set to nil at top of function
+}
+
+extern Slice runtime_CPUProfile(void)
+ __asm__("libgo_runtime.runtime.CPUProfile");
+
+// CPUProfile returns the next cpu profile block as a []byte.
+// The user documentation is in debug.go.
+Slice
+runtime_CPUProfile(void)
+{
+ return getprofile(prof);
+}
projects / gcc.git / commitdiff