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runtime: eliminate rendundant loads gcPercent

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The previous change was an automated change that made gcPercent a
type-safe atomic variable. However, that introduced a lot of redundant
formal atomic loads of the variable. Remove them by only loading once in
each case, and reusing the value.

Change-Id: I49647135f423574f94506d456d1cc390150fad02
Reviewed-on: https://go-review.googlesource.com/c/go/+/357795
Trust: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
This commit is contained in:
Michael Anthony Knyszek 2021-10-21 21:26:50 +00:00 committed by Michael Knyszek
parent 2f71c86370
commit 09e8de70c2
1 changed files with 10 additions and 9 deletions
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19
src/runtime/mgcpacer.go
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@ -966,8 +966,8 @@ func (c *gcControllerState) commit(triggerRatio float64) {
// has grown by GOGC/100 over where it started the last cycle, // has grown by GOGC/100 over where it started the last cycle,
// plus additional runway for non-heap sources of GC work. // plus additional runway for non-heap sources of GC work.
goal := ^uint64(0) goal := ^uint64(0)
if c.gcPercent.Load() >= 0 { if gcPercent := c.gcPercent.Load(); gcPercent >= 0 {
goal = c.heapMarked + (c.heapMarked+atomic.Load64(&c.stackScan)+atomic.Load64(&c.globalsScan))*uint64(c.gcPercent.Load())/100 goal = c.heapMarked + (c.heapMarked+atomic.Load64(&c.stackScan)+atomic.Load64(&c.globalsScan))*uint64(gcPercent)/100
} }
// Don't trigger below the minimum heap size. // Don't trigger below the minimum heap size.
@ -1081,17 +1081,19 @@ func (c *gcControllerState) commit(triggerRatio float64) {
// //
// For !goexperiment.PacerRedesign. // For !goexperiment.PacerRedesign.
func (c *gcControllerState) oldCommit(triggerRatio float64) { func (c *gcControllerState) oldCommit(triggerRatio float64) {
gcPercent := c.gcPercent.Load()
// Compute the next GC goal, which is when the allocated heap // Compute the next GC goal, which is when the allocated heap
// has grown by GOGC/100 over the heap marked by the last // has grown by GOGC/100 over the heap marked by the last
// cycle. // cycle.
goal := ^uint64(0) goal := ^uint64(0)
if c.gcPercent.Load() >= 0 { if gcPercent >= 0 {
goal = c.heapMarked + c.heapMarked*uint64(c.gcPercent.Load())/100 goal = c.heapMarked + c.heapMarked*uint64(gcPercent)/100
} }
// Set the trigger ratio, capped to reasonable bounds. // Set the trigger ratio, capped to reasonable bounds.
if c.gcPercent.Load() >= 0 { if gcPercent >= 0 {
scalingFactor := float64(c.gcPercent.Load()) / 100 scalingFactor := float64(gcPercent) / 100
// Ensure there's always a little margin so that the // Ensure there's always a little margin so that the
// mutator assist ratio isn't infinity. // mutator assist ratio isn't infinity.
maxTriggerRatio := 0.95 * scalingFactor maxTriggerRatio := 0.95 * scalingFactor
@ -1131,7 +1133,7 @@ func (c *gcControllerState) oldCommit(triggerRatio float64) {
// We trigger the next GC cycle when the allocated heap has // We trigger the next GC cycle when the allocated heap has
// grown by the trigger ratio over the marked heap size. // grown by the trigger ratio over the marked heap size.
trigger := ^uint64(0) trigger := ^uint64(0)
if c.gcPercent.Load() >= 0 { if gcPercent >= 0 {
trigger = uint64(float64(c.heapMarked) * (1 + triggerRatio)) trigger = uint64(float64(c.heapMarked) * (1 + triggerRatio))
// Don't trigger below the minimum heap size. // Don't trigger below the minimum heap size.
minTrigger := c.heapMinimum minTrigger := c.heapMinimum
@ -1211,9 +1213,8 @@ func (c *gcControllerState) setGCPercent(in int32) int32 {
if in < 0 { if in < 0 {
in = -1 in = -1
} }
// Write it atomically so readers like revise() can read it safely. c.heapMinimum = defaultHeapMinimum * uint64(in) / 100
c.gcPercent.Store(in) c.gcPercent.Store(in)
c.heapMinimum = defaultHeapMinimum * uint64(c.gcPercent.Load()) / 100
// Update pacing in response to gcPercent change. // Update pacing in response to gcPercent change.
c.commit(c.triggerRatio) c.commit(c.triggerRatio)