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runtime: separate GC background utilization from goal utilization

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Currently these are the same constant, but are separate concepts.
Split them into two constants for easier experimentation and better
documentation.

Change-Id: I121854d4fd1a4a827f727c8e5153160c24aacda7
Reviewed-on: https://go-review.googlesource.com/68570
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>
This commit is contained in:
Austin Clements 2017-10-04 17:12:28 -04:00
parent 504a305c62
commit 27923482fa
1 changed files with 13 additions and 7 deletions
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20
src/runtime/mgc.go
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@ -299,10 +299,10 @@ const (
// gcMarkWorkerFractionalMode indicates that a P is currently
// running the "fractional" mark worker. The fractional worker
// is necessary when GOMAXPROCS*gcGoalUtilization is not an
// integer. The fractional worker should run until it is
// is necessary when GOMAXPROCS*gcBackgroundUtilization is not
// an integer. The fractional worker should run until it is
// preempted and will be scheduled to pick up the fractional
// part of GOMAXPROCS*gcGoalUtilization.
// part of GOMAXPROCS*gcBackgroundUtilization.
gcMarkWorkerFractionalMode
// gcMarkWorkerIdleMode indicates that a P is running the mark
@ -453,9 +453,9 @@ func (c *gcControllerState) startCycle() {
memstats.next_gc = memstats.heap_live + 1024*1024
}
// Compute the total mark utilization goal and divide it among
// Compute the background mark utilization goal and divide it among
// dedicated and fractional workers.
totalUtilizationGoal := float64(gomaxprocs) * gcGoalUtilization
totalUtilizationGoal := float64(gomaxprocs) * gcBackgroundUtilization
c.dedicatedMarkWorkersNeeded = int64(totalUtilizationGoal)
c.fractionalUtilizationGoal = totalUtilizationGoal - float64(c.dedicatedMarkWorkersNeeded)
if c.fractionalUtilizationGoal > 0 {
@ -566,7 +566,7 @@ func (c *gcControllerState) endCycle() float64 {
assistDuration := nanotime() - c.markStartTime
// Assume background mark hit its utilization goal.
utilization := gcGoalUtilization
utilization := gcBackgroundUtilization
// Add assist utilization; avoid divide by zero.
if assistDuration > 0 {
utilization += float64(c.assistTime) / float64(assistDuration*int64(gomaxprocs))
@ -856,10 +856,16 @@ func gcSetTriggerRatio(triggerRatio float64) {
}
}
// gcGoalUtilization is the goal CPU utilization for background
// gcGoalUtilization is the goal CPU utilization for
// marking as a fraction of GOMAXPROCS.
const gcGoalUtilization = 0.25
// gcBackgroundUtilization is the fixed CPU utilization for background
// marking. It must be <= gcGoalUtilization. The difference between
// gcGoalUtilization and gcBackgroundUtilization will be made up by
// mark assists.
const gcBackgroundUtilization = 0.25
// gcCreditSlack is the amount of scan work credit that can can
// accumulate locally before updating gcController.scanWork and,
// optionally, gcController.bgScanCredit. Lower values give a more