runtime: give 2 words back in notetsleep_internal

I really hoped we could avoid this nonsense, but it appears not.

Should fix windows/amd64 build breakage.

TBR=iant
CC=golang-codereviews
https://golang.org/cl/137120043

diff --git a/src/pkg/runtime/lock_sema.go b/src/pkg/runtime/lock_sema.go
index e0476f329120b27af460e228d15adcc76dfbdcef..d136b828061d8206a641864ad49b7ef38c51feda 100644 (file)
--- a/src/pkg/runtime/lock_sema.go
+++ b/src/pkg/runtime/lock_sema.go
@@ -173,8 +173,13 @@ func notesleep(n *note) {
 }
 
 //go:nosplit
-func notetsleep_internal(n *note, ns int64) bool {
-       gp := getg()
+func notetsleep_internal(n *note, ns int64, gp *g, deadline int64) bool {
+       // gp and deadline are logically local variables, but they are written
+       // as parameters so that the stack space they require is charged
+       // to the caller.
+       // This reduces the nosplit footprint of notetsleep_internal.
+       gp = getg()
+
        // Register for wakeup on n->waitm.
        if !casuintptr(&n.key, 0, uintptr(unsafe.Pointer(gp.m))) {
                // Must be locked (got wakeup).
@@ -190,7 +195,8 @@ func notetsleep_internal(n *note, ns int64) bool {
                gp.m.blocked = false
                return true
        }
-       deadline := nanotime() + ns
+
+       deadline = nanotime() + ns
        for {
                // Registered.  Sleep.
                gp.m.blocked = true
@@ -244,7 +250,7 @@ func notetsleep(n *note, ns int64) bool {
        if gp.m.waitsema == 0 {
                gp.m.waitsema = semacreate()
        }
-       return notetsleep_internal(n, ns)
+       return notetsleep_internal(n, ns, nil, 0)
 }
 
 // same as runtime·notetsleep, but called on user g (not g0)
@@ -258,7 +264,7 @@ func notetsleepg(n *note, ns int64) bool {
                gp.m.waitsema = semacreate()
        }
        entersyscallblock()
-       ok := notetsleep_internal(n, ns)
+       ok := notetsleep_internal(n, ns, nil, 0)
        exitsyscall()
        return ok
 }