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Revert "runtime: prepare for extensions to waiting M list"

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This reverts commit be0b569caa (CL 585635).

Reason for revert: This is part of a patch series that changed the
handling of contended lock2/unlock2 calls, reducing the maximum
throughput of contended runtime.mutex values, and causing a performance
regression on applications where that is (or became) the bottleneck.

Updates #66999
Updates #67585

Change-Id: I7843ccaecbd273b7ceacfa0f420dd993b4b15a0a
Reviewed-on: https://go-review.googlesource.com/c/go/+/589117
Auto-Submit: Rhys Hiltner <rhys.hiltner@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
This commit is contained in:
Rhys Hiltner 2024-05-29 16:43:38 +00:00 committed by Gopher Robot
parent 3f4be127bc
commit 9114c51521
3 changed files with 6 additions and 17 deletions
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10
src/runtime/lock_sema.go
View File

@ -77,11 +77,11 @@ Loop:
osyield()
} else {
// Someone else has it.
// l.key points to a linked list of M's waiting
// for this lock, chained through m.mWaitList.next.
// l->waitm points to a linked list of M's waiting
// for this lock, chained through m->nextwaitm.
// Queue this M.
for {
gp.m.mWaitList.next = muintptr(v &^ locked)
gp.m.nextwaitm = muintptr(v &^ locked)
if atomic.Casuintptr(&l.key, v, uintptr(unsafe.Pointer(gp.m))|locked) {
break
}
@ -119,7 +119,7 @@ func unlock2(l *mutex) {
// Other M's are waiting for the lock.
// Dequeue an M.
mp = muintptr(v &^ locked).ptr()
if atomic.Casuintptr(&l.key, v, uintptr(mp.mWaitList.next)) {
if atomic.Casuintptr(&l.key, v, uintptr(mp.nextwaitm)) {
// Dequeued an M. Wake it.
semawakeup(mp)
break
@ -200,7 +200,7 @@ func notetsleep_internal(n *note, ns int64, gp *g, deadline int64) bool {
// This reduces the nosplit footprint of notetsleep_internal.
gp = getg()
// Register for wakeup on n.key.
// Register for wakeup on n->waitm.
if !atomic.Casuintptr(&n.key, 0, uintptr(unsafe.Pointer(gp.m))) {
// Must be locked (got wakeup).
if n.key != locked {

11
src/runtime/mprof.go
View File

@ -667,17 +667,6 @@ func (lt *lockTimer) end() {
}
}
// mWaitList is part of the M struct, and holds the list of Ms that are waiting
// for a particular runtime.mutex.
//
// When an M is unable to immediately obtain a lock, it adds itself to the list
// of Ms waiting for the lock. It does that via this struct's next field,
// forming a singly-linked list with the mutex's key field pointing to the head
// of the list.
type mWaitList struct {
next muintptr // next m waiting for lock (set by us, cleared by another during unlock)
}
type mLockProfile struct {
waitTime atomic.Int64 // total nanoseconds spent waiting in runtime.lockWithRank
stack []uintptr // stack that experienced contention in runtime.lockWithRank

2
src/runtime/runtime2.go
View File

@ -596,8 +596,8 @@ type m struct {
createstack [32]uintptr // stack that created this thread, it's used for StackRecord.Stack0, so it must align with it.
lockedExt uint32 // tracking for external LockOSThread
lockedInt uint32 // tracking for internal lockOSThread
nextwaitm muintptr // next m waiting for lock
mWaitList mWaitList // list of runtime lock waiters
mLockProfile mLockProfile // fields relating to runtime.lock contention
profStack []uintptr // used for memory/block/mutex stack traces