diff --git a/src/runtime/proc.go b/src/runtime/proc.go index 44dbb2fd44b..61364d91ff9 100644 --- a/src/runtime/proc.go +++ b/src/runtime/proc.go @@ -7507,23 +7507,36 @@ func runqgrab(pp *p, batch *[256]guintptr, batchHead uint32, stealRunNextG bool) // Try to steal from pp.runnext. if next := pp.runnext; next != 0 { if pp.status == _Prunning { - // Sleep to ensure that pp isn't about to run the g - // we are about to steal. - // The important use case here is when the g running - // on pp ready()s another g and then almost - // immediately blocks. Instead of stealing runnext - // in this window, back off to give pp a chance to - // schedule runnext. This will avoid thrashing gs - // between different Ps. - // A sync chan send/recv takes ~50ns as of time of - // writing, so 3us gives ~50x overshoot. - if !osHasLowResTimer { - usleep(3) - } else { - // On some platforms system timer granularity is - // 1-15ms, which is way too much for this - // optimization. So just yield. - osyield() + if mp := pp.m.ptr(); mp != nil { + if gp := mp.curg; gp == nil || readgstatus(gp)&^_Gscan != _Gsyscall { + // Sleep to ensure that pp isn't about to run the g + // we are about to steal. + // The important use case here is when the g running + // on pp ready()s another g and then almost + // immediately blocks. Instead of stealing runnext + // in this window, back off to give pp a chance to + // schedule runnext. This will avoid thrashing gs + // between different Ps. + // A sync chan send/recv takes ~50ns as of time of + // writing, so 3us gives ~50x overshoot. + // If curg is nil, we assume that the P is likely + // to be in the scheduler. If curg isn't nil and isn't + // in a syscall, then it's either running, waiting, or + // runnable. In this case we want to sleep because the + // P might either call into the scheduler soon (running), + // or already is (since we found a waiting or runnable + // goroutine hanging off of a running P, suggesting it + // either recently transitioned out of running, or will + // transition to running shortly). + if !osHasLowResTimer { + usleep(3) + } else { + // On some platforms system timer granularity is + // 1-15ms, which is way too much for this + // optimization. So just yield. + osyield() + } + } } } if !pp.runnext.cas(next, 0) {