runtime: unroll gc_m loop

The loop made more sense when gc_m was not its own function.

Change-Id: I71a7f21d777e69c1924e3b534c507476daa4dfdd
Reviewed-on: https://go-review.googlesource.com/5332
Reviewed-by: Austin Clements <austin@google.com>

diff --git a/src/runtime/mgc.go b/src/runtime/mgc.go
index 079856ed705412c5212c068c60ad133da3722657..4adc0f4fbe859abf756480614d8c4c3ff55f6a92 100644 (file)
--- a/src/runtime/mgc.go
+++ b/src/runtime/mgc.go
@@ -362,20 +362,9 @@ func gc(mode int) {
        // the root set down a bit (g0 stacks are not scanned, and
        // we don't need to scan gc's internal state).  We also
        // need to switch to g0 so we can shrink the stack.
-       n := 1
-       if debug.gctrace > 1 {
-               n = 2
-       }
-       for i := 0; i < n; i++ {
-               if i > 0 {
-                       // refresh start time if doing a second GC
-                       startTime = nanotime()
-               }
-               // switch to g0, call gc, then switch back
-               systemstack(func() {
-                       gc_m(startTime, mode == gcForceBlockMode)
-               })
-       }
+       systemstack(func() {
+               gc_m(startTime, mode == gcForceBlockMode)
+       })
 
        systemstack(func() {
                // Called from malloc.go using systemstack.
@@ -397,6 +386,13 @@ func gc(mode int) {
                gc_m(startTime, mode == gcForceBlockMode) // turns off checkmarkphase + calls clearcheckmarkbits
        })
 
+       if debug.gctrace > 1 {
+               startTime = nanotime()
+               systemstack(func() {
+                       gc_m(startTime, mode == gcForceBlockMode)
+               })
+       }
+
        if trace.enabled {
                traceGCDone()
                traceGoStart()