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runtime: move debug checks behind constant flag in mallocgc

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These debug checks are very occasionally helpful, but they do cost real
time. The biggest issue seems to be the bloat of mallocgc due to the
"throw" paths. Overall, after some follow-ups, this change cuts about
1ns off of the mallocgc fast path.

This is a microoptimization that on its own changes very little, but
together with other optimizations and a breaking up of the various
malloc paths will matter all together ("death by a thousand cuts").

Change-Id: I07c4547ad724b9f94281320846677fb558957721
Reviewed-on: https://go-review.googlesource.com/c/go/+/617878
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Michael Anthony Knyszek 2024-10-03 18:30:15 +00:00 committed by Gopher Robot
parent e750a0cdb3
commit 6686edc0e7
2 changed files with 22 additions and 7 deletions
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26
src/runtime/malloc.go
View File

@ -972,6 +972,14 @@ func (c *mcache) nextFree(spc spanClass) (v gclinkptr, s *mspan, checkGCTrigger
return
}
// doubleCheckMalloc enables a bunch of extra checks to malloc to double-check
// that various invariants are upheld.
//
// We might consider turning these on by default; many of them previously were.
// They account for a few % of mallocgc's cost though, which does matter somewhat
// at scale.
const doubleCheckMalloc = false
// Allocate an object of size bytes.
// Small objects are allocated from the per-P cache's free lists.
// Large objects (> 32 kB) are allocated straight from the heap.
@ -991,8 +999,10 @@ func (c *mcache) nextFree(spc spanClass) (v gclinkptr, s *mspan, checkGCTrigger
//
//go:linkname mallocgc
func mallocgc(size uintptr, typ *_type, needzero bool) unsafe.Pointer {
if gcphase == _GCmarktermination {
throw("mallocgc called with gcphase == _GCmarktermination")
if doubleCheckMalloc {
if gcphase == _GCmarktermination {
throw("mallocgc called with gcphase == _GCmarktermination")
}
}
if size == 0 {
@ -1049,11 +1059,13 @@ func mallocgc(size uintptr, typ *_type, needzero bool) unsafe.Pointer {
// Set mp.mallocing to keep from being preempted by GC.
mp := acquirem()
if mp.mallocing != 0 {
throw("malloc deadlock")
}
if mp.gsignal == getg() {
throw("malloc during signal")
if doubleCheckMalloc {
if mp.mallocing != 0 {
throw("malloc deadlock")
}
if mp.gsignal == getg() {
throw("malloc during signal")
}
}
mp.mallocing = 1

3
src/runtime/mgcmark.go
View File

@ -1694,6 +1694,9 @@ func gcmarknewobject(span *mspan, obj uintptr) {
if useCheckmark { // The world should be stopped so this should not happen.
throw("gcmarknewobject called while doing checkmark")
}
if gcphase == _GCmarktermination {
throw("mallocgc called with gcphase == _GCmarktermination")
}
// Mark object.
objIndex := span.objIndex(obj)