runtime: include bootstrap m in mcpu accounting

R=rsc, dvyukov
CC=golang-dev
https://golang.org/cl/5307052

diff --git a/src/pkg/runtime/proc.c b/src/pkg/runtime/proc.c
index 468960d17729be3924d87fffc816565a4621ce1e..3408c06f69f12c08f88d073586483e9d91922dd0 100644 (file)
--- a/src/pkg/runtime/proc.c
+++ b/src/pkg/runtime/proc.c
@@ -128,6 +128,8 @@ Sched runtime·sched;
 int32 runtime·gomaxprocs;
 bool runtime·singleproc;
 
+static bool canaddmcpu(void);
+
 // An m that is waiting for notewakeup(&m->havenextg).  This may
 // only be accessed while the scheduler lock is held.  This is used to
 // minimize the number of times we call notewakeup while the scheduler
@@ -202,6 +204,10 @@ runtime·schedinit(void)
        setmcpumax(runtime·gomaxprocs);
        runtime·singleproc = runtime·gomaxprocs == 1;
 
+       canaddmcpu();   // mcpu++ to account for bootstrap m
+       m->helpgc = 1;  // flag to tell schedule() to mcpu--
+       runtime·sched.grunning++;
+
        mstats.enablegc = 1;
        m->nomemprof--;
 }
@@ -811,6 +817,7 @@ schedule(G *gp)
                        readylocked(gp);
                }
        } else if(m->helpgc) {
+               // Bootstrap m or new m started by starttheworld.
                // atomic { mcpu-- }
                v = runtime·xadd(&runtime·sched.atomic, -1<<mcpuShift);
                if(atomic_mcpu(v) > maxgomaxprocs)
@@ -818,6 +825,10 @@ schedule(G *gp)
                // Compensate for increment in starttheworld().
                runtime·sched.grunning--;
                m->helpgc = 0;
+       } else if(m->nextg != nil) {
+               // New m started by matchmg.
+       } else {
+               runtime·throw("invalid m state in scheduler");
        }
 
        // Find (or wait for) g to run.  Unlocks runtime·sched.