diff options
Diffstat (limited to 'src/runtime/debug.go')
| -rw-r--r-- | src/runtime/debug.go | 68 |
1 files changed, 65 insertions, 3 deletions
diff --git a/src/runtime/debug.go b/src/runtime/debug.go index 57e9ba8d7d..94d1dab34d 100644 --- a/src/runtime/debug.go +++ b/src/runtime/debug.go @@ -10,9 +10,28 @@ import ( ) // GOMAXPROCS sets the maximum number of CPUs that can be executing -// simultaneously and returns the previous setting. It defaults to -// the value of [runtime.NumCPU]. If n < 1, it does not change the current setting. -// This call will go away when the scheduler improves. +// simultaneously and returns the previous setting. If n < 1, it does not change +// the current setting. +// +// If the GOMAXPROCS environment variable is set to a positive whole number, +// GOMAXPROCS defaults to that value. +// +// Otherwise, the Go runtime selects an appropriate default value based on the +// number of logical CPUs on the machine, the process’s CPU affinity mask, and, +// on Linux, the process’s average CPU throughput limit based on cgroup CPU +// quota, if any. +// +// The Go runtime periodically updates the default value based on changes to +// the total logical CPU count, the CPU affinity mask, or cgroup quota. Setting +// a custom value with the GOMAXPROCS environment variable or by calling +// GOMAXPROCS disables automatic updates. The default value and automatic +// updates can be restored by calling [SetDefaultGOMAXPROCS]. +// +// If GODEBUG=containermaxprocs=0 is set, GOMAXPROCS defaults to the value of +// [runtime.NumCPU]. If GODEBUG=updatemaxprocs=0 is set, the Go runtime does +// not perform automatic GOMAXPROCS updating. +// +// The default GOMAXPROCS behavior may change as the scheduler improves. func GOMAXPROCS(n int) int { if GOARCH == "wasm" && n > 1 { n = 1 // WebAssembly has no threads yet, so only one CPU is possible. @@ -28,12 +47,55 @@ func GOMAXPROCS(n int) int { stw := stopTheWorldGC(stwGOMAXPROCS) // newprocs will be processed by startTheWorld + // + // TODO(prattmic): this could use a nicer API. Perhaps add it to the + // stw parameter? newprocs = int32(n) + newprocsCustom = true startTheWorldGC(stw) return ret } +// SetDefaultGOMAXPROCS updates the GOMAXPROCS setting to the runtime +// default, as described by [GOMAXPROCS], ignoring the GOMAXPROCS +// environment variable. +// +// SetDefaultGOMAXPROCS can be used to enable the default automatic updating +// GOMAXPROCS behavior if it has been disabled by the GOMAXPROCS +// environment variable or a prior call to [GOMAXPROCS], or to force an immediate +// update if the caller is aware of a change to the total logical CPU count, CPU +// affinity mask or cgroup quota. +func SetDefaultGOMAXPROCS() { + // SetDefaultGOMAXPROCS conceptually means "[re]do what the runtime + // would do at startup if the GOMAXPROCS environment variable were + // unset." It still respects GODEBUG. + + procs := defaultGOMAXPROCS(0) + + lock(&sched.lock) + curr := gomaxprocs + custom := sched.customGOMAXPROCS + unlock(&sched.lock) + + if !custom && procs == curr { + // Nothing to do if we're already using automatic GOMAXPROCS + // and the limit is unchanged. + return + } + + stw := stopTheWorldGC(stwGOMAXPROCS) + + // newprocs will be processed by startTheWorld + // + // TODO(prattmic): this could use a nicer API. Perhaps add it to the + // stw parameter? + newprocs = procs + newprocsCustom = false + + startTheWorldGC(stw) +} + // NumCPU returns the number of logical CPUs usable by the current process. // // The set of available CPUs is checked by querying the operating system |