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runtime: control background scan credit flushing with flag

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Currently callers of gcDrain control whether it flushes scan work
credit to gcController.bgScanCredit by passing a value other than -1
for the flush threshold. Shortly we're going to make this always flush
scan work to gcController.scanWork and optionally also flush scan work
to gcController.bgScanCredit. This will be much easier if the flush
threshold is simply a constant (which it is in practice) and callers
merely control whether or not the flush includes the background
credit. Hence, replace the flush threshold argument with a flag.

Change-Id: Ia27db17de8a3f1e462a5d7137d4b5dc72f99a04e
Reviewed-on: https://go-review.googlesource.com/15406
Reviewed-by: Rick Hudson <rlh@golang.org>
This commit is contained in:
Austin Clements 2015-10-04 22:47:27 -04:00
parent 9b3cdaf0a3
commit c18b163c15
2 changed files with 14 additions and 12 deletions
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8
src/runtime/mgc.go
View File

@ -1334,7 +1334,7 @@ func gcBgMarkWorker(p *p) {
default:
throw("gcBgMarkWorker: unexpected gcMarkWorkerMode")
case gcMarkWorkerDedicatedMode:
gcDrain(&p.gcw, gcBgCreditSlack, gcDrainBlock)
gcDrain(&p.gcw, gcDrainBlock|gcDrainFlushBgCredit)
// gcDrain did the xadd(&work.nwait +1) to
// match the decrement above. It only returns
// at a mark completion point.
@ -1343,7 +1343,7 @@ func gcBgMarkWorker(p *p) {
throw("gcDrain returned with buffer")
}
case gcMarkWorkerFractionalMode, gcMarkWorkerIdleMode:
gcDrain(&p.gcw, gcBgCreditSlack, gcDrainUntilPreempt)
gcDrain(&p.gcw, gcDrainUntilPreempt|gcDrainFlushBgCredit)
// If we are nearing the end of mark, dispose
// of the cache promptly. We must do this
@ -1454,7 +1454,7 @@ func gcMark(start_time int64) {
parfordo(work.markfor)
var gcw gcWork
gcDrain(&gcw, -1, gcDrainBlock)
gcDrain(&gcw, gcDrainBlock)
gcw.dispose()
if work.full != 0 {
@ -1717,7 +1717,7 @@ func gchelper() {
parfordo(work.markfor)
if gcphase != _GCscan {
var gcw gcWork
gcDrain(&gcw, -1, gcDrainBlock) // blocks in getfull
gcDrain(&gcw, gcDrainBlock) // blocks in getfull
gcw.dispose()
}

18
src/runtime/mgcmark.go
View File

@ -553,6 +553,7 @@ type gcDrainFlags int
const (
gcDrainUntilPreempt gcDrainFlags = 1 << iota
gcDrainFlushBgCredit
// gcDrainBlock is the opposite of gcDrainUntilPreempt. This
// is the default, but callers should use the constant for
@ -567,21 +568,22 @@ const (
// g.preempt is set. Otherwise, this will block until all dedicated
// workers are blocked in gcDrain.
//
// If flushScanCredit != -1, gcDrain flushes accumulated scan work
// credit to gcController.bgScanCredit whenever gcw's local scan work
// credit exceeds flushScanCredit.
// If flags&gcDrainFlushBgCredit != 0, gcDrain flushes scan work
// credit to gcController.bgScanCredit every gcBgCreditSlack units of
// scan work.
//go:nowritebarrier
func gcDrain(gcw *gcWork, flushScanCredit int64, flags gcDrainFlags) {
func gcDrain(gcw *gcWork, flags gcDrainFlags) {
if !writeBarrierEnabled {
throw("gcDrain phase incorrect")
}
blocking := flags&gcDrainUntilPreempt == 0
flushBgCredit := flags&gcDrainFlushBgCredit != 0
var lastScanFlush, nextScanFlush int64
if flushScanCredit != -1 {
if flushBgCredit {
lastScanFlush = gcw.scanWork
nextScanFlush = lastScanFlush + flushScanCredit
nextScanFlush = lastScanFlush + gcBgCreditSlack
} else {
nextScanFlush = int64(^uint64(0) >> 1)
}
@ -618,10 +620,10 @@ func gcDrain(gcw *gcWork, flushScanCredit int64, flags gcDrainFlags) {
credit := gcw.scanWork - lastScanFlush
xaddint64(&gcController.bgScanCredit, credit)
lastScanFlush = gcw.scanWork
nextScanFlush = lastScanFlush + flushScanCredit
nextScanFlush = lastScanFlush + gcBgCreditSlack
}
}
if flushScanCredit != -1 {
if flushBgCredit {
credit := gcw.scanWork - lastScanFlush
xaddint64(&gcController.bgScanCredit, credit)
}