The logic to trigger periodic GC is such that if GC is disabled but at least one GC cycle has ever happened (e.g., GC was disabled at runtime by SetGCPercent(-1) or runtime.GC() was called), then once the periodic GC period has elapsed (2 minutes by default), sysmon will attempt to trigger a GC every 10ms. This GC will be a no-op, but it still goes through the motions of waking the goroutine and prints a gctrace line.

The following program demonstrates this:

package main

import "runtime"

func main() {
	runtime.GC()
	for {
		fib(10)
	}
}

func fib(n int) int {
	if n <= 2 {
		return 1
	}
	return fib(n-1) + fib(n-2)
}

If run with GODEBUG=gctrace=1 GOGC=off ./test, then after two minutes the runtime will print GC forced every 10ms. (If you don't want to wait two minutes, add forcegcperiod = 10 * 1e9 to sysmon.)

AFAIK this isn't happening in the wild. I found this while reworking the triggering logic.

/cc @RLH