runtime: capture per-m trace state in a type

More tightening up of the tracer's interface.

While we're here, clarify why waittraceskip isn't included by explaining
what the wait* fields in the M are really for.

Change-Id: I0e7b4cac79fb77a7a0b3ca6b6cc267668e3610bc
Reviewed-on: https://go-review.googlesource.com/c/go/+/494190
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go
index 9e702aa033396e057d3f2ce84686fffa59b3e687..0350052a25caa75a178a87d48cece4e1ca157bb3 100644 (file)
--- a/src/runtime/runtime2.go
+++ b/src/runtime/runtime2.go
@@ -577,13 +577,17 @@ type m struct {
        lockedExt     uint32      // tracking for external LockOSThread
        lockedInt     uint32      // tracking for internal lockOSThread
        nextwaitm     muintptr    // next m waiting for lock
+
+       // wait* are used to carry arguments from gopark into park_m, because
+       // there's no stack to put them on. That is their sole purpose.
        waitunlockf   func(*g, unsafe.Pointer) bool
        waitlock      unsafe.Pointer
        waittraceev   byte
        waittraceskip int
-       startingtrace bool
-       syscalltick   uint32
-       freelink      *m // on sched.freem
+
+       syscalltick uint32
+       freelink    *m // on sched.freem
+       trace       mTraceState
 
        // these are here because they are too large to be on the stack
        // of low-level NOSPLIT functions.

diff --git a/src/runtime/trace.go b/src/runtime/trace.go
index 5daf3beb7739908c5d1589516beb5a46bac3d620..465e000c0e1ce27442d91e294fed0a981aea7b38 100644 (file)
--- a/src/runtime/trace.go
+++ b/src/runtime/trace.go
@@ -169,6 +169,11 @@ type gTraceState struct {
        lastP          puintptr // last P emitted an event for this goroutine
 }
 
+// mTraceState is per-M state for the tracer.
+type mTraceState struct {
+       startingTrace bool // this M is in TraceStart, potentially before traceEnabled is true
+}
+
 // traceLockInit initializes global trace locks.
 func traceLockInit() {
        lockInit(&trace.bufLock, lockRankTraceBuf)
@@ -252,10 +257,10 @@ func StartTrace() error {
        // That would lead to an inconsistent trace:
        // - either GoSysExit appears before EvGoInSyscall,
        // - or GoSysExit appears for a goroutine for which we don't emit EvGoInSyscall below.
-       // To instruct traceEvent that it must not ignore events below, we set startingtrace.
+       // To instruct traceEvent that it must not ignore events below, we set trace.startingTrace.
        // trace.enabled is set afterwards once we have emitted all preliminary events.
        mp := getg().m
-       mp.startingtrace = true
+       mp.trace.startingTrace = true
 
        // Obtain current stack ID to use in all traceEvGoCreate events below.
        stkBuf := make([]uintptr, traceStackSize)
@@ -324,7 +329,7 @@ func StartTrace() error {
        trace.strings = make(map[string]uint64)
 
        trace.seqGC = 0
-       mp.startingtrace = false
+       mp.trace.startingTrace = false
        trace.enabled = true
 
        // Register runtime goroutine labels.
@@ -698,7 +703,7 @@ func traceEvent(ev byte, skip int, args ...uint64) {
        // during tracing in exitsyscall is resolved by locking trace.bufLock in traceLockBuffer.
        //
        // Note trace_userTaskCreate runs the same check.
-       if !trace.enabled && !mp.startingtrace {
+       if !trace.enabled && !mp.trace.startingTrace {
                traceReleaseBuffer(mp, pid)
                return
        }
@@ -1642,7 +1647,7 @@ func trace_userTaskCreate(id, parentID uint64, taskType string) {
 
        // Same as in traceEvent.
        mp, pid, bufp := traceAcquireBuffer()
-       if !trace.enabled && !mp.startingtrace {
+       if !trace.enabled && !mp.trace.startingTrace {
                traceReleaseBuffer(mp, pid)
                return
        }
@@ -1664,7 +1669,7 @@ func trace_userRegion(id, mode uint64, name string) {
        }
 
        mp, pid, bufp := traceAcquireBuffer()
-       if !trace.enabled && !mp.startingtrace {
+       if !trace.enabled && !mp.trace.startingTrace {
                traceReleaseBuffer(mp, pid)
                return
        }
@@ -1681,7 +1686,7 @@ func trace_userLog(id uint64, category, message string) {
        }
 
        mp, pid, bufp := traceAcquireBuffer()
-       if !trace.enabled && !mp.startingtrace {
+       if !trace.enabled && !mp.trace.startingTrace {
                traceReleaseBuffer(mp, pid)
                return
        }