runtime: disable use of runnext on wasm

When readying a goroutine, the scheduler typically places the readied
goroutine in pp.runnext, which will typically be the next goroutine to
run in the schedule.

In order to prevent a set of ping-pong goroutines from simply switching
back and forth via runnext and starving the rest of the run queue, a
goroutine scheduled via runnext shares a time slice (pp.schedtick) with
the previous goroutine.

sysmon detects "long-running goroutines", which really means Ps using
the same pp.schedtick for too long, and preempts them to allow the rest
of the run queue to run. Thus this avoids starvation via runnext.

However, wasm has no threads, and thus no sysmon. Without sysmon to
preempt, the possibility for starvation returns. Avoid this by disabling
runnext entirely on wasm. This means that readied goroutines always go
on the end of the run queue and thus cannot starve via runnext.

Note that this CL doesn't do anything about single long-running
goroutines. Without sysmon to preempt them, a single goroutine that
fails to yield will starve the run queue indefinitely.

For #65178.

Change-Id: I10859d088776125a2af8c9cd862b6e071da628b5
Cq-Include-Trybots: luci.golang.try:gotip-js-wasm,gotip-wasip1-wasm_wasmtime,gotip-wasip1-wasm_wazero
Reviewed-on: https://go-review.googlesource.com/c/go/+/559798
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

1 files changed, 0 insertions, 5 deletions

diff --git a/src/time/sleep_test.go b/src/time/sleep_test.go
index 1ebc2d3c6a..e985870710 100644
--- a/src/time/sleep_test.go
+++ b/src/time/sleep_test.go
@@ -111,11 +111,6 @@ func TestAfterFuncStarvation(t *testing.T) {
 	// the AfterFunc goroutine instead of the runnable channel goroutine.
 	// However, in https://go.dev/issue/65178 this was observed to live-lock
 	// on wasip1/wasm and js/wasm after <10000 runs.
-
-	if runtime.GOARCH == "wasm" {
-		testenv.SkipFlaky(t, 65178)
-	}
-
 	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(1))
 
 	var (