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runtime: move roots' bases calculation to gcMarkRootPrepare

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This patch provides changes according to Austin's TODO. It just moves
calculation of base indexes of each root type from markroot function
to gcMarkRootPrepare.

Change-Id: Ib231de34e7f81e922762fc3ee2b1830921c0c7cf
Reviewed-on: https://go-review.googlesource.com/c/go/+/279461
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Austin Clements <austin@google.com>
This commit is contained in:
Ruslan Andreev 2020-12-22 19:22:14 +08:00 committed by Austin Clements
parent ab02cbd29f
commit 82e4a6310b
2 changed files with 22 additions and 19 deletions
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4
src/runtime/mgc.go
View File

@ -328,6 +328,10 @@ var work struct {
nFlushCacheRoots int
nDataRoots, nBSSRoots, nSpanRoots, nStackRoots int
// Base indexes of each root type. Set by gcMarkRootPrepare.
baseFlushCache uint32
baseData, baseBSS, baseSpans, baseStacks, baseEnd uint32
// Each type of GC state transition is protected by a lock.
// Since multiple threads can simultaneously detect the state
// transition condition, any thread that detects a transition

37
src/runtime/mgcmark.go
View File

@ -106,6 +106,14 @@ func gcMarkRootPrepare() {
work.markrootNext = 0
work.markrootJobs = uint32(fixedRootCount + work.nFlushCacheRoots + work.nDataRoots + work.nBSSRoots + work.nSpanRoots + work.nStackRoots)
// Calculate base indexes of each root type
work.baseFlushCache = uint32(fixedRootCount)
work.baseData = work.baseFlushCache + uint32(work.nFlushCacheRoots)
work.baseBSS = work.baseData + uint32(work.nDataRoots)
work.baseSpans = work.baseBSS + uint32(work.nBSSRoots)
work.baseStacks = work.baseSpans + uint32(work.nSpanRoots)
work.baseEnd = work.baseStacks + uint32(work.nStackRoots)
}
// gcMarkRootCheck checks that all roots have been scanned. It is
@ -149,28 +157,19 @@ var oneptrmask = [...]uint8{1}
//
//go:nowritebarrier
func markroot(gcw *gcWork, i uint32) {
// TODO(austin): This is a bit ridiculous. Compute and store
// the bases in gcMarkRootPrepare instead of the counts.
baseFlushCache := uint32(fixedRootCount)
baseData := baseFlushCache + uint32(work.nFlushCacheRoots)
baseBSS := baseData + uint32(work.nDataRoots)
baseSpans := baseBSS + uint32(work.nBSSRoots)
baseStacks := baseSpans + uint32(work.nSpanRoots)
end := baseStacks + uint32(work.nStackRoots)
// Note: if you add a case here, please also update heapdump.go:dumproots.
switch {
case baseFlushCache <= i && i < baseData:
flushmcache(int(i - baseFlushCache))
case work.baseFlushCache <= i && i < work.baseData:
flushmcache(int(i - work.baseFlushCache))
case baseData <= i && i < baseBSS:
case work.baseData <= i && i < work.baseBSS:
for _, datap := range activeModules() {
markrootBlock(datap.data, datap.edata-datap.data, datap.gcdatamask.bytedata, gcw, int(i-baseData))
markrootBlock(datap.data, datap.edata-datap.data, datap.gcdatamask.bytedata, gcw, int(i-work.baseData))
}
case baseBSS <= i && i < baseSpans:
case work.baseBSS <= i && i < work.baseSpans:
for _, datap := range activeModules() {
markrootBlock(datap.bss, datap.ebss-datap.bss, datap.gcbssmask.bytedata, gcw, int(i-baseBSS))
markrootBlock(datap.bss, datap.ebss-datap.bss, datap.gcbssmask.bytedata, gcw, int(i-work.baseBSS))
}
case i == fixedRootFinalizers:
@ -184,18 +183,18 @@ func markroot(gcw *gcWork, i uint32) {
// stackfree.
systemstack(markrootFreeGStacks)
case baseSpans <= i && i < baseStacks:
case work.baseSpans <= i && i < work.baseStacks:
// mark mspan.specials
markrootSpans(gcw, int(i-baseSpans))
markrootSpans(gcw, int(i-work.baseSpans))
default:
// the rest is scanning goroutine stacks
var gp *g
if baseStacks <= i && i < end {
if work.baseStacks <= i && i < work.baseEnd {
// N.B. Atomic read of allglen in gcMarkRootPrepare
// acts as a barrier to ensure that allgs must be large
// enough to contain all relevant Gs.
gp = allgs[i-baseStacks]
gp = allgs[i-work.baseStacks]
} else {
throw("markroot: bad index")
}