From ae7943e11b41b5ee98279bf0574942e09f15ce20 Mon Sep 17 00:00:00 2001 From: Ian Lance Taylor Date: Sun, 25 Jul 2021 16:26:13 -0700 Subject: [PATCH] [release-branch.go1.16] runtime: remove adjustTimers counter In CL 336432 we changed adjusttimers so that it no longer cleared timerModifiedEarliest if there were no timersModifiedEarlier timers. This caused some Google internal tests to time out, presumably due to the increased contention on timersLock. We can avoid that by simply not skipping the loop in adjusttimers, which lets us safely clear timerModifiedEarliest. And if we don't skip the loop, then there isn't much reason to keep the count of timerModifiedEarlier timers at all. So remove it. The effect will be that for programs that create some timerModifiedEarlier timers and then remove them all, the program will do an occasional additional loop over all the timers. And, programs that have some timerModifiedEarlier timers will always loop over all the timers, without the quicker exit when they have all been seen. But the loops should not occur all that often, due to timerModifiedEarliest. For #47329 For #47332 Change-Id: I7b244c1244d97b169a3c7fbc8f8a8b115731ddee Reviewed-on: https://go-review.googlesource.com/c/go/+/337309 Trust: Ian Lance Taylor Run-TryBot: Ian Lance Taylor TryBot-Result: Go Bot Reviewed-by: Michael Pratt (cherry picked from commit bfbb288574841f2db2499a580d7bf985a5df4556) Reviewed-on: https://go-review.googlesource.com/c/go/+/338649 --- src/runtime/proc.go | 1 - src/runtime/runtime2.go | 6 ----- src/runtime/time.go | 53 +++++++---------------------------------- 3 files changed, 8 insertions(+), 52 deletions(-) diff --git a/src/runtime/proc.go b/src/runtime/proc.go index cf9770587aa2c..3ace2b329bb76 100644 --- a/src/runtime/proc.go +++ b/src/runtime/proc.go @@ -4751,7 +4751,6 @@ func (pp *p) destroy() { moveTimers(plocal, pp.timers) pp.timers = nil pp.numTimers = 0 - pp.adjustTimers = 0 pp.deletedTimers = 0 atomic.Store64(&pp.timer0When, 0) unlock(&pp.timersLock) diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go index dd375da1936c5..e9825327d105d 100644 --- a/src/runtime/runtime2.go +++ b/src/runtime/runtime2.go @@ -699,12 +699,6 @@ type p struct { // Modified using atomic instructions. numTimers uint32 - // Number of timerModifiedEarlier timers on P's heap. - // This should only be modified while holding timersLock, - // or while the timer status is in a transient state - // such as timerModifying. - adjustTimers uint32 - // Number of timerDeleted timers in P's heap. // Modified using atomic instructions. deletedTimers uint32 diff --git a/src/runtime/time.go b/src/runtime/time.go index 7b84d2af57151..666b242316416 100644 --- a/src/runtime/time.go +++ b/src/runtime/time.go @@ -333,7 +333,6 @@ func deltimer(t *timer) bool { // Must fetch t.pp before setting status // to timerDeleted. tpp := t.pp.ptr() - atomic.Xadd(&tpp.adjustTimers, -1) if !atomic.Cas(&t.status, timerModifying, timerDeleted) { badTimer() } @@ -510,20 +509,9 @@ loop: tpp := t.pp.ptr() - // Update the adjustTimers field. Subtract one if we - // are removing a timerModifiedEarlier, add one if we - // are adding a timerModifiedEarlier. - adjust := int32(0) - if status == timerModifiedEarlier { - adjust-- - } if newStatus == timerModifiedEarlier { - adjust++ updateTimerModifiedEarliest(tpp, when) } - if adjust != 0 { - atomic.Xadd(&tpp.adjustTimers, adjust) - } // Set the new status of the timer. if !atomic.Cas(&t.status, timerModifying, newStatus) { @@ -591,9 +579,6 @@ func cleantimers(pp *p) { // Move t to the right position. dodeltimer0(pp) doaddtimer(pp, t) - if s == timerModifiedEarlier { - atomic.Xadd(&pp.adjustTimers, -1) - } if !atomic.Cas(&t.status, timerMoving, timerWaiting) { badTimer() } @@ -664,32 +649,23 @@ func moveTimers(pp *p, timers []*timer) { // it also moves timers that have been modified to run later, // and removes deleted timers. The caller must have locked the timers for pp. func adjusttimers(pp *p, now int64) { - if atomic.Load(&pp.adjustTimers) == 0 { - if verifyTimers { - verifyTimerHeap(pp) - } - return - } - // If we haven't yet reached the time of the first timerModifiedEarlier // timer, don't do anything. This speeds up programs that adjust // a lot of timers back and forth if the timers rarely expire. // We'll postpone looking through all the adjusted timers until // one would actually expire. - if first := atomic.Load64(&pp.timerModifiedEarliest); first != 0 { - if int64(first) > now { - if verifyTimers { - verifyTimerHeap(pp) - } - return + first := atomic.Load64(&pp.timerModifiedEarliest) + if first == 0 || int64(first) > now { + if verifyTimers { + verifyTimerHeap(pp) } - - // We are going to clear all timerModifiedEarlier timers. - atomic.Store64(&pp.timerModifiedEarliest, 0) + return } + // We are going to clear all timerModifiedEarlier timers. + atomic.Store64(&pp.timerModifiedEarliest, 0) + var moved []*timer -loop: for i := 0; i < len(pp.timers); i++ { t := pp.timers[i] if t.pp.ptr() != pp { @@ -716,11 +692,6 @@ loop: // loop to skip some other timer. dodeltimer(pp, i) moved = append(moved, t) - if s == timerModifiedEarlier { - if n := atomic.Xadd(&pp.adjustTimers, -1); int32(n) <= 0 { - break loop - } - } // Look at this heap position again. i-- } @@ -819,9 +790,6 @@ func runtimer(pp *p, now int64) int64 { t.when = t.nextwhen dodeltimer0(pp) doaddtimer(pp, t) - if s == timerModifiedEarlier { - atomic.Xadd(&pp.adjustTimers, -1) - } if !atomic.Cas(&t.status, timerMoving, timerWaiting) { badTimer() } @@ -916,7 +884,6 @@ func clearDeletedTimers(pp *p) { atomic.Store64(&pp.timerModifiedEarliest, 0) cdel := int32(0) - cearlier := int32(0) to := 0 changedHeap := false timers := pp.timers @@ -941,9 +908,6 @@ nextTimer: if !atomic.Cas(&t.status, timerMoving, timerWaiting) { badTimer() } - if s == timerModifiedEarlier { - cearlier++ - } continue nextTimer } case timerDeleted: @@ -980,7 +944,6 @@ nextTimer: atomic.Xadd(&pp.deletedTimers, -cdel) atomic.Xadd(&pp.numTimers, -cdel) - atomic.Xadd(&pp.adjustTimers, -cearlier) timers = timers[:to] pp.timers = timers