runtime: remove work.pauseStart

Most of the uses of work.pauseStart are completely useless, it could
simply be a local variable. One use passes a parameter from gcMarkDone
to gcMarkTermination, but that could simply be an argument.

Keeping this field in workType makes it seems more important than it
really is, so just drop it.

Change-Id: I2fdc0b21f8844e5e7be47148c3e10f13e49815c6
Reviewed-on: https://go-review.googlesource.com/c/go/+/542075
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

diff --git a/src/runtime/mgc.go b/src/runtime/mgc.go
index c8a58de969f3edabd90e0e927c6edde63752084a..e9130a782004f406814e1b88393b01eb5ed02a1b 100644 (file)
--- a/src/runtime/mgc.go
+++ b/src/runtime/mgc.go
@@ -419,7 +419,6 @@ type workType struct {
        tSweepTerm, tMark, tMarkTerm, tEnd int64 // nanotime() of phase start
 
        pauseNS    int64 // total STW time this cycle
-       pauseStart int64 // nanotime() of last STW
 
        // debug.gctrace heap sizes for this cycle.
        heap0, heap1, heap2 uint64
@@ -677,7 +676,7 @@ func gcStart(trigger gcTrigger) {
 
        now := nanotime()
        work.tSweepTerm = now
-       work.pauseStart = now
+       pauseStart := now
        systemstack(func() { stopTheWorldWithSema(stwGCSweepTerm) })
        // Finish sweep before we start concurrent scan.
        systemstack(func() {
@@ -744,9 +743,9 @@ func gcStart(trigger gcTrigger) {
        // Concurrent mark.
        systemstack(func() {
                now = startTheWorldWithSema()
-               work.pauseNS += now - work.pauseStart
+               work.pauseNS += now - pauseStart
                work.tMark = now
-               memstats.gcPauseDist.record(now - work.pauseStart)
+               memstats.gcPauseDist.record(now - pauseStart)
 
                sweepTermCpu := int64(work.stwprocs) * (work.tMark - work.tSweepTerm)
                work.cpuStats.gcPauseTime += sweepTermCpu
@@ -858,7 +857,7 @@ top:
        // shaded. Transition to mark termination.
        now := nanotime()
        work.tMarkTerm = now
-       work.pauseStart = now
+       pauseStart := now
        getg().m.preemptoff = "gcing"
        systemstack(func() { stopTheWorldWithSema(stwGCMarkTerm) })
        // The gcphase is _GCmark, it will transition to _GCmarktermination
@@ -888,8 +887,8 @@ top:
                getg().m.preemptoff = ""
                systemstack(func() {
                        now := startTheWorldWithSema()
-                       work.pauseNS += now - work.pauseStart
-                       memstats.gcPauseDist.record(now - work.pauseStart)
+                       work.pauseNS += now - pauseStart
+                       memstats.gcPauseDist.record(now - pauseStart)
                })
                semrelease(&worldsema)
                goto top
@@ -923,12 +922,12 @@ top:
        gcController.endCycle(now, int(gomaxprocs), work.userForced)
 
        // Perform mark termination. This will restart the world.
-       gcMarkTermination()
+       gcMarkTermination(pauseStart)
 }
 
 // World must be stopped and mark assists and background workers must be
 // disabled.
-func gcMarkTermination() {
+func gcMarkTermination(pauseStart int64) {
        // Start marktermination (write barrier remains enabled for now).
        setGCPhase(_GCmarktermination)
 
@@ -1009,9 +1008,9 @@ func gcMarkTermination() {
        now := nanotime()
        sec, nsec, _ := time_now()
        unixNow := sec*1e9 + int64(nsec)
-       work.pauseNS += now - work.pauseStart
+       work.pauseNS += now - pauseStart
        work.tEnd = now
-       memstats.gcPauseDist.record(now - work.pauseStart)
+       memstats.gcPauseDist.record(now - pauseStart)
        atomic.Store64(&memstats.last_gc_unix, uint64(unixNow)) // must be Unix time to make sense to user
        atomic.Store64(&memstats.last_gc_nanotime, uint64(now)) // monotonic time for us
        memstats.pause_ns[memstats.numgc%uint32(len(memstats.pause_ns))] = uint64(work.pauseNS)