Golang篇-深入理解GMP调度模型

Golang篇-深入理解GMP调度模型 - 麦奇

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携程是 go 中的一大特色，其占用较低的内存，通过携程使我们的应用能支持更大的并发，下面我们来剖析他的工作原理

runtime/runtime2.go

type g struct {
	// Stack parameters.
	// stack describes the actual stack memory: [stack.lo, stack.hi).
	// stackguard0 is the stack pointer compared in the Go stack growth prologue.
	// It is stack.lo+StackGuard normally, but can be StackPreempt to trigger a preemption.
	// stackguard1 is the stack pointer compared in the C stack growth prologue.
	// It is stack.lo+StackGuard on g0 and gsignal stacks.
	// It is ~0 on other goroutine stacks, to trigger a call to morestackc (and crash).
	stack       stack   // offset known to runtime/cgo
	stackguard0 uintptr // offset known to liblink
	stackguard1 uintptr // offset known to liblink

_panic    *_panic // innermost panic - offset known to liblink
	_defer    *_defer // innermost defer
	m         *m      // current m; offset known to arm liblink
	sched     gobuf
	syscallsp uintptr // if status==Gsyscall, syscallsp = sched.sp to use during gc
	syscallpc uintptr // if status==Gsyscall, syscallpc = sched.pc to use during gc
	stktopsp  uintptr // expected sp at top of stack, to check in traceback
	// param is a generic pointer parameter field used to pass
	// values in particular contexts where other storage for the
	// parameter would be difficult to find. It is currently used
	// in three ways:
	// 1. When a channel operation wakes up a blocked goroutine, it sets param to
	//    point to the sudog of the completed blocking operation.
	// 2. By gcAssistAlloc1 to signal back to its caller that the goroutine completed
	//    the GC cycle. It is unsafe to do so in any other way, because the goroutine's
	//    stack may have moved in the meantime.
	// 3. By debugCallWrap to pass parameters to a new goroutine because allocating a
	//    closure in the runtime is forbidden.
	param        unsafe.Pointer
	atomicstatus atomic.Uint32
	stackLock    uint32 // sigprof/scang lock; TODO: fold in to atomicstatus
	goid         uint64 //协程id
	schedlink    guintptr
	waitsince    int64      // approx time when the g become blocked
	waitreason   waitReason // if status==Gwaiting

preempt       bool // preemption signal, duplicates stackguard0 = stackpreempt
	preemptStop   bool // transition to _Gpreempted on preemption; otherwise, just deschedule
	preemptShrink bool // shrink stack at synchronous safe point

// asyncSafePoint is set if g is stopped at an asynchronous
	// safe point. This means there are frames on the stack
	// without precise pointer information.
	asyncSafePoint bool

paniconfault bool // panic (instead of crash) on unexpected fault address
	gcscandone   bool // g has scanned stack; protected by _Gscan bit in status
	throwsplit   bool // must not split stack
	// activeStackChans indicates that there are unlocked channels
	// pointing into this goroutine's stack. If true, stack
	// copying needs to acquire channel locks to protect these
	// areas of the stack.
	activeStackChans bool
	// parkingOnChan indicates that the goroutine is about to
	// park on a chansend or chanrecv. Used to signal an unsafe point
	// for stack shrinking.
	parkingOnChan atomic.Bool

raceignore     int8     // ignore race detection events
	sysblocktraced bool     // StartTrace has emitted EvGoInSyscall about this goroutine
	tracking       bool     // whether we're tracking this G for sched latency statistics
	trackingSeq    uint8    // used to decide whether to track this G
	trackingStamp  int64    // timestamp of when the G last started being tracked
	runnableTime   int64    // the amount of time spent runnable, cleared when running, only used when tracking
	sysexitticks   int64    // cputicks when syscall has returned (for tracing)
	traceseq       uint64   // trace event sequencer
	tracelastp     puintptr // last P emitted an event for this goroutine
	lockedm        muintptr
	sig            uint32
	writebuf       []byte
	sigcode0       uintptr
	sigcode1       uintptr
	sigpc          uintptr
	gopc           uintptr         // pc of go statement that created this goroutine
	ancestors      *[]ancestorInfo // ancestor information goroutine(s) that created this goroutine (only used if debug.tracebackancestors)
	startpc        uintptr         // pc of goroutine function
	racectx        uintptr
	waiting        *sudog         // sudog structures this g is waiting on (that have a valid elem ptr); in lock order
	cgoCtxt        []uintptr      // cgo traceback context
	labels         unsafe.Pointer // profiler labels
	timer          *timer         // cached timer for time.Sleep
	selectDone     atomic.Uint32  // are we participating in a select and did someone win the race?

// goroutineProfiled indicates the status of this goroutine's stack for the
	// current in-progress goroutine profile
	goroutineProfiled goroutineProfileStateHolder

// Per-G GC state

// gcAssistBytes is this G's GC assist credit in terms of
	// bytes allocated. If this is positive, then the G has credit
	// to allocate gcAssistBytes bytes without assisting. If this
	// is negative, then the G must correct this by performing
	// scan work. We track this in bytes to make it fast to update
	// and check for debt in the malloc hot path. The assist ratio
	// determines how this corresponds to scan work debt.
	gcAssistBytes int64
}

type m struct {
	g0      *g     // goroutine with scheduling stack
	morebuf gobuf  // gobuf arg to morestack
	divmod  uint32 // div/mod denominator for arm - known to liblink
	_       uint32 // align next field to 8 bytes

// Fields not known to debuggers.
	procid        uint64            // for debuggers, but offset not hard-coded
	gsignal       *g                // signal-handling g
	goSigStack    gsignalStack      // Go-allocated signal handling stack
	sigmask       sigset            // storage for saved signal mask
	tls           [tlsSlots]uintptr // thread-local storage (for x86 extern register)
	mstartfn      func()
	curg          *g       // current running goroutine
	caughtsig     guintptr // goroutine running during fatal signal
	p             puintptr // attached p for executing go code (nil if not executing go code)
	nextp         puintptr
	oldp          puintptr // the p that was attached before executing a syscall
	id            int64
	mallocing     int32
	throwing      throwType
	preemptoff    string // if != "", keep curg running on this m
	locks         int32
	dying         int32
	profilehz     int32
	spinning      bool // m is out of work and is actively looking for work
	blocked       bool // m is blocked on a note
	newSigstack   bool // minit on C thread called sigaltstack
	printlock     int8
	incgo         bool          // m is executing a cgo call
	isextra       bool          // m is an extra m
	freeWait      atomic.Uint32 // Whether it is safe to free g0 and delete m (one of freeMRef, freeMStack, freeMWait)
	fastrand      uint64
	needextram    bool
	traceback     uint8
	ncgocall      uint64        // number of cgo calls in total
	ncgo          int32         // number of cgo calls currently in progress
	cgoCallersUse atomic.Uint32 // if non-zero, cgoCallers in use temporarily
	cgoCallers    *cgoCallers   // cgo traceback if crashing in cgo call
	park          note
	alllink       *m // on allm
	schedlink     muintptr
	lockedg       guintptr
	createstack   [32]uintptr // stack that created this thread.
	lockedExt     uint32      // tracking for external LockOSThread
	lockedInt     uint32      // tracking for internal lockOSThread
	nextwaitm     muintptr    // next m waiting for lock
	waitunlockf   func(*g, unsafe.Pointer) bool
	waitlock      unsafe.Pointer
	waittraceev   byte
	waittraceskip int
	startingtrace bool
	syscalltick   uint32
	freelink      *m // on sched.freem

// these are here because they are too large to be on the stack
	// of low-level NOSPLIT functions.
	libcall   libcall
	libcallpc uintptr // for cpu profiler
	libcallsp uintptr
	libcallg  guintptr
	syscall   libcall // stores syscall parameters on windows

vdsoSP uintptr // SP for traceback while in VDSO call (0 if not in call)
	vdsoPC uintptr // PC for traceback while in VDSO call

// preemptGen counts the number of completed preemption
	// signals. This is used to detect when a preemption is
	// requested, but fails.
	preemptGen atomic.Uint32

// Whether this is a pending preemption signal on this M.
	signalPending atomic.Uint32

dlogPerM

mOS

// Up to 10 locks held by this m, maintained by the lock ranking code.
	locksHeldLen int
	locksHeld    [10]heldLockInfo
}

type p struct {
	id          int32
	status      uint32 // one of pidle/prunning/...
	link        puintptr
	schedtick   uint32     // incremented on every scheduler call
	syscalltick uint32     // incremented on every system call
	sysmontick  sysmontick // last tick observed by sysmon
	m           muintptr   // back-link to associated m (nil if idle)
	mcache      *mcache
	pcache      pageCache
	raceprocctx uintptr

deferpool    []*_defer // pool of available defer structs (see panic.go)
	deferpoolbuf [32]*_defer

// Cache of goroutine ids, amortizes accesses to runtime·sched.goidgen.
	goidcache    uint64
	goidcacheend uint64

// Queue of runnable goroutines. Accessed without lock.
	runqhead uint32
	runqtail uint32
	runq     [256]guintptr
	// runnext, if non-nil, is a runnable G that was ready'd by
	// the current G and should be run next instead of what's in
	// runq if there's time remaining in the running G's time
	// slice. It will inherit the time left in the current time
	// slice. If a set of goroutines is locked in a
	// communicate-and-wait pattern, this schedules that set as a
	// unit and eliminates the (potentially large) scheduling
	// latency that otherwise arises from adding the ready'd
	// goroutines to the end of the run queue.
	//
	// Note that while other P's may atomically CAS this to zero,
	// only the owner P can CAS it to a valid G.
	runnext guintptr

// Available G's (status == Gdead)
	gFree struct {
		gList
		n int32
	}

sudogcache []*sudog
	sudogbuf   [128]*sudog

// Cache of mspan objects from the heap.
	mspancache struct {
		// We need an explicit length here because this field is used
		// in allocation codepaths where write barriers are not allowed,
		// and eliminating the write barrier/keeping it eliminated from
		// slice updates is tricky, moreso than just managing the length
		// ourselves.
		len int
		buf [128]*mspan
	}

tracebuf traceBufPtr

// traceSweep indicates the sweep events should be traced.
	// This is used to defer the sweep start event until a span
	// has actually been swept.
	traceSweep bool
	// traceSwept and traceReclaimed track the number of bytes
	// swept and reclaimed by sweeping in the current sweep loop.
	traceSwept, traceReclaimed uintptr

palloc persistentAlloc // per-P to avoid mutex

// The when field of the first entry on the timer heap.
	// This is 0 if the timer heap is empty.
	timer0When atomic.Int64

// The earliest known nextwhen field of a timer with
	// timerModifiedEarlier status. Because the timer may have been
	// modified again, there need not be any timer with this value.
	// This is 0 if there are no timerModifiedEarlier timers.
	timerModifiedEarliest atomic.Int64

// Per-P GC state
	gcAssistTime         int64 // Nanoseconds in assistAlloc
	gcFractionalMarkTime int64 // Nanoseconds in fractional mark worker (atomic)

// limiterEvent tracks events for the GC CPU limiter.
	limiterEvent limiterEvent

// gcMarkWorkerMode is the mode for the next mark worker to run in.
	// That is, this is used to communicate with the worker goroutine
	// selected for immediate execution by
	// gcController.findRunnableGCWorker. When scheduling other goroutines,
	// this field must be set to gcMarkWorkerNotWorker.
	gcMarkWorkerMode gcMarkWorkerMode
	// gcMarkWorkerStartTime is the nanotime() at which the most recent
	// mark worker started.
	gcMarkWorkerStartTime int64

// gcw is this P's GC work buffer cache. The work buffer is
	// filled by write barriers, drained by mutator assists, and
	// disposed on certain GC state transitions.
	gcw gcWork

// wbBuf is this P's GC write barrier buffer.
	//
	// TODO: Consider caching this in the running G.
	wbBuf wbBuf

runSafePointFn uint32 // if 1, run sched.safePointFn at next safe point

// statsSeq is a counter indicating whether this P is currently
	// writing any stats. Its value is even when not, odd when it is.
	statsSeq atomic.Uint32

// Lock for timers. We normally access the timers while running
	// on this P, but the scheduler can also do it from a different P.
	timersLock mutex

// Actions to take at some time. This is used to implement the
	// standard library's time package.
	// Must hold timersLock to access.
	timers []*timer

// Number of timers in P's heap.
	numTimers atomic.Uint32

// Number of timerDeleted timers in P's heap.
	deletedTimers atomic.Uint32

// Race context used while executing timer functions.
	timerRaceCtx uintptr

// maxStackScanDelta accumulates the amount of stack space held by
	// live goroutines (i.e. those eligible for stack scanning).
	// Flushed to gcController.maxStackScan once maxStackScanSlack
	// or -maxStackScanSlack is reached.
	maxStackScanDelta int64

// gc-time statistics about current goroutines
	// Note that this differs from maxStackScan in that this
	// accumulates the actual stack observed to be used at GC time (hi - sp),
	// not an instantaneous measure of the total stack size that might need
	// to be scanned (hi - lo).
	scannedStackSize uint64 // stack size of goroutines scanned by this P
	scannedStacks    uint64 // number of goroutines scanned by this P

// preempt is set to indicate that this P should be enter the
	// scheduler ASAP (regardless of what G is running on it).
	preempt bool

// pageTraceBuf is a buffer for writing out page allocation/free/scavenge traces.
	//
	// Used only if GOEXPERIMENT=pagetrace.
	pageTraceBuf pageTraceBuf

// Padding is no longer needed. False sharing is now not a worry because p is large enough
	// that its size class is an integer multiple of the cache line size (for any of our architectures).
}

https://github.com/golang/go