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Diffstat (limited to 'src/runtime/mstats.go')
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diff --git a/src/runtime/mstats.go b/src/runtime/mstats.go new file mode 100644 index 0000000..87afec4 --- /dev/null +++ b/src/runtime/mstats.go @@ -0,0 +1,977 @@ +// Copyright 2009 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +// Memory statistics + +package runtime + +import ( + "runtime/internal/atomic" + "unsafe" +) + +type mstats struct { + // Statistics about malloc heap. + heapStats consistentHeapStats + + // Statistics about stacks. + stacks_sys sysMemStat // only counts newosproc0 stack in mstats; differs from MemStats.StackSys + + // Statistics about allocation of low-level fixed-size structures. + mspan_sys sysMemStat + mcache_sys sysMemStat + buckhash_sys sysMemStat // profiling bucket hash table + + // Statistics about GC overhead. + gcMiscSys sysMemStat // updated atomically or during STW + + // Miscellaneous statistics. + other_sys sysMemStat // updated atomically or during STW + + // Statistics about the garbage collector. + + // Protected by mheap or worldsema during GC. + last_gc_unix uint64 // last gc (in unix time) + pause_total_ns uint64 + pause_ns [256]uint64 // circular buffer of recent gc pause lengths + pause_end [256]uint64 // circular buffer of recent gc end times (nanoseconds since 1970) + numgc uint32 + numforcedgc uint32 // number of user-forced GCs + gc_cpu_fraction float64 // fraction of CPU time used by GC + + last_gc_nanotime uint64 // last gc (monotonic time) + lastHeapInUse uint64 // heapInUse at mark termination of the previous GC + + enablegc bool +} + +var memstats mstats + +// A MemStats records statistics about the memory allocator. +type MemStats struct { + // General statistics. + + // Alloc is bytes of allocated heap objects. + // + // This is the same as HeapAlloc (see below). + Alloc uint64 + + // TotalAlloc is cumulative bytes allocated for heap objects. + // + // TotalAlloc increases as heap objects are allocated, but + // unlike Alloc and HeapAlloc, it does not decrease when + // objects are freed. + TotalAlloc uint64 + + // Sys is the total bytes of memory obtained from the OS. + // + // Sys is the sum of the XSys fields below. Sys measures the + // virtual address space reserved by the Go runtime for the + // heap, stacks, and other internal data structures. It's + // likely that not all of the virtual address space is backed + // by physical memory at any given moment, though in general + // it all was at some point. + Sys uint64 + + // Lookups is the number of pointer lookups performed by the + // runtime. + // + // This is primarily useful for debugging runtime internals. + Lookups uint64 + + // Mallocs is the cumulative count of heap objects allocated. + // The number of live objects is Mallocs - Frees. + Mallocs uint64 + + // Frees is the cumulative count of heap objects freed. + Frees uint64 + + // Heap memory statistics. + // + // Interpreting the heap statistics requires some knowledge of + // how Go organizes memory. Go divides the virtual address + // space of the heap into "spans", which are contiguous + // regions of memory 8K or larger. A span may be in one of + // three states: + // + // An "idle" span contains no objects or other data. The + // physical memory backing an idle span can be released back + // to the OS (but the virtual address space never is), or it + // can be converted into an "in use" or "stack" span. + // + // An "in use" span contains at least one heap object and may + // have free space available to allocate more heap objects. + // + // A "stack" span is used for goroutine stacks. Stack spans + // are not considered part of the heap. A span can change + // between heap and stack memory; it is never used for both + // simultaneously. + + // HeapAlloc is bytes of allocated heap objects. + // + // "Allocated" heap objects include all reachable objects, as + // well as unreachable objects that the garbage collector has + // not yet freed. Specifically, HeapAlloc increases as heap + // objects are allocated and decreases as the heap is swept + // and unreachable objects are freed. Sweeping occurs + // incrementally between GC cycles, so these two processes + // occur simultaneously, and as a result HeapAlloc tends to + // change smoothly (in contrast with the sawtooth that is + // typical of stop-the-world garbage collectors). + HeapAlloc uint64 + + // HeapSys is bytes of heap memory obtained from the OS. + // + // HeapSys measures the amount of virtual address space + // reserved for the heap. This includes virtual address space + // that has been reserved but not yet used, which consumes no + // physical memory, but tends to be small, as well as virtual + // address space for which the physical memory has been + // returned to the OS after it became unused (see HeapReleased + // for a measure of the latter). + // + // HeapSys estimates the largest size the heap has had. + HeapSys uint64 + + // HeapIdle is bytes in idle (unused) spans. + // + // Idle spans have no objects in them. These spans could be + // (and may already have been) returned to the OS, or they can + // be reused for heap allocations, or they can be reused as + // stack memory. + // + // HeapIdle minus HeapReleased estimates the amount of memory + // that could be returned to the OS, but is being retained by + // the runtime so it can grow the heap without requesting more + // memory from the OS. If this difference is significantly + // larger than the heap size, it indicates there was a recent + // transient spike in live heap size. + HeapIdle uint64 + + // HeapInuse is bytes in in-use spans. + // + // In-use spans have at least one object in them. These spans + // can only be used for other objects of roughly the same + // size. + // + // HeapInuse minus HeapAlloc estimates the amount of memory + // that has been dedicated to particular size classes, but is + // not currently being used. This is an upper bound on + // fragmentation, but in general this memory can be reused + // efficiently. + HeapInuse uint64 + + // HeapReleased is bytes of physical memory returned to the OS. + // + // This counts heap memory from idle spans that was returned + // to the OS and has not yet been reacquired for the heap. + HeapReleased uint64 + + // HeapObjects is the number of allocated heap objects. + // + // Like HeapAlloc, this increases as objects are allocated and + // decreases as the heap is swept and unreachable objects are + // freed. + HeapObjects uint64 + + // Stack memory statistics. + // + // Stacks are not considered part of the heap, but the runtime + // can reuse a span of heap memory for stack memory, and + // vice-versa. + + // StackInuse is bytes in stack spans. + // + // In-use stack spans have at least one stack in them. These + // spans can only be used for other stacks of the same size. + // + // There is no StackIdle because unused stack spans are + // returned to the heap (and hence counted toward HeapIdle). + StackInuse uint64 + + // StackSys is bytes of stack memory obtained from the OS. + // + // StackSys is StackInuse, plus any memory obtained directly + // from the OS for OS thread stacks. + // + // In non-cgo programs this metric is currently equal to StackInuse + // (but this should not be relied upon, and the value may change in + // the future). + // + // In cgo programs this metric includes OS thread stacks allocated + // directly from the OS. Currently, this only accounts for one stack in + // c-shared and c-archive build modes and other sources of stacks from + // the OS (notably, any allocated by C code) are not currently measured. + // Note this too may change in the future. + StackSys uint64 + + // Off-heap memory statistics. + // + // The following statistics measure runtime-internal + // structures that are not allocated from heap memory (usually + // because they are part of implementing the heap). Unlike + // heap or stack memory, any memory allocated to these + // structures is dedicated to these structures. + // + // These are primarily useful for debugging runtime memory + // overheads. + + // MSpanInuse is bytes of allocated mspan structures. + MSpanInuse uint64 + + // MSpanSys is bytes of memory obtained from the OS for mspan + // structures. + MSpanSys uint64 + + // MCacheInuse is bytes of allocated mcache structures. + MCacheInuse uint64 + + // MCacheSys is bytes of memory obtained from the OS for + // mcache structures. + MCacheSys uint64 + + // BuckHashSys is bytes of memory in profiling bucket hash tables. + BuckHashSys uint64 + + // GCSys is bytes of memory in garbage collection metadata. + GCSys uint64 + + // OtherSys is bytes of memory in miscellaneous off-heap + // runtime allocations. + OtherSys uint64 + + // Garbage collector statistics. + + // NextGC is the target heap size of the next GC cycle. + // + // The garbage collector's goal is to keep HeapAlloc ≤ NextGC. + // At the end of each GC cycle, the target for the next cycle + // is computed based on the amount of reachable data and the + // value of GOGC. + NextGC uint64 + + // LastGC is the time the last garbage collection finished, as + // nanoseconds since 1970 (the UNIX epoch). + LastGC uint64 + + // PauseTotalNs is the cumulative nanoseconds in GC + // stop-the-world pauses since the program started. + // + // During a stop-the-world pause, all goroutines are paused + // and only the garbage collector can run. + PauseTotalNs uint64 + + // PauseNs is a circular buffer of recent GC stop-the-world + // pause times in nanoseconds. + // + // The most recent pause is at PauseNs[(NumGC+255)%256]. In + // general, PauseNs[N%256] records the time paused in the most + // recent N%256th GC cycle. There may be multiple pauses per + // GC cycle; this is the sum of all pauses during a cycle. + PauseNs [256]uint64 + + // PauseEnd is a circular buffer of recent GC pause end times, + // as nanoseconds since 1970 (the UNIX epoch). + // + // This buffer is filled the same way as PauseNs. There may be + // multiple pauses per GC cycle; this records the end of the + // last pause in a cycle. + PauseEnd [256]uint64 + + // NumGC is the number of completed GC cycles. + NumGC uint32 + + // NumForcedGC is the number of GC cycles that were forced by + // the application calling the GC function. + NumForcedGC uint32 + + // GCCPUFraction is the fraction of this program's available + // CPU time used by the GC since the program started. + // + // GCCPUFraction is expressed as a number between 0 and 1, + // where 0 means GC has consumed none of this program's CPU. A + // program's available CPU time is defined as the integral of + // GOMAXPROCS since the program started. That is, if + // GOMAXPROCS is 2 and a program has been running for 10 + // seconds, its "available CPU" is 20 seconds. GCCPUFraction + // does not include CPU time used for write barrier activity. + // + // This is the same as the fraction of CPU reported by + // GODEBUG=gctrace=1. + GCCPUFraction float64 + + // EnableGC indicates that GC is enabled. It is always true, + // even if GOGC=off. + EnableGC bool + + // DebugGC is currently unused. + DebugGC bool + + // BySize reports per-size class allocation statistics. + // + // BySize[N] gives statistics for allocations of size S where + // BySize[N-1].Size < S ≤ BySize[N].Size. + // + // This does not report allocations larger than BySize[60].Size. + BySize [61]struct { + // Size is the maximum byte size of an object in this + // size class. + Size uint32 + + // Mallocs is the cumulative count of heap objects + // allocated in this size class. The cumulative bytes + // of allocation is Size*Mallocs. The number of live + // objects in this size class is Mallocs - Frees. + Mallocs uint64 + + // Frees is the cumulative count of heap objects freed + // in this size class. + Frees uint64 + } +} + +func init() { + if offset := unsafe.Offsetof(memstats.heapStats); offset%8 != 0 { + println(offset) + throw("memstats.heapStats not aligned to 8 bytes") + } + // Ensure the size of heapStatsDelta causes adjacent fields/slots (e.g. + // [3]heapStatsDelta) to be 8-byte aligned. + if size := unsafe.Sizeof(heapStatsDelta{}); size%8 != 0 { + println(size) + throw("heapStatsDelta not a multiple of 8 bytes in size") + } +} + +// ReadMemStats populates m with memory allocator statistics. +// +// The returned memory allocator statistics are up to date as of the +// call to ReadMemStats. This is in contrast with a heap profile, +// which is a snapshot as of the most recently completed garbage +// collection cycle. +func ReadMemStats(m *MemStats) { + _ = m.Alloc // nil check test before we switch stacks, see issue 61158 + stw := stopTheWorld(stwReadMemStats) + + systemstack(func() { + readmemstats_m(m) + }) + + startTheWorld(stw) +} + +// doubleCheckReadMemStats controls a double-check mode for ReadMemStats that +// ensures consistency between the values that ReadMemStats is using and the +// runtime-internal stats. +var doubleCheckReadMemStats = false + +// readmemstats_m populates stats for internal runtime values. +// +// The world must be stopped. +func readmemstats_m(stats *MemStats) { + assertWorldStopped() + + // Flush mcaches to mcentral before doing anything else. + // + // Flushing to the mcentral may in general cause stats to + // change as mcentral data structures are manipulated. + systemstack(flushallmcaches) + + // Calculate memory allocator stats. + // During program execution we only count number of frees and amount of freed memory. + // Current number of alive objects in the heap and amount of alive heap memory + // are calculated by scanning all spans. + // Total number of mallocs is calculated as number of frees plus number of alive objects. + // Similarly, total amount of allocated memory is calculated as amount of freed memory + // plus amount of alive heap memory. + + // Collect consistent stats, which are the source-of-truth in some cases. + var consStats heapStatsDelta + memstats.heapStats.unsafeRead(&consStats) + + // Collect large allocation stats. + totalAlloc := consStats.largeAlloc + nMalloc := consStats.largeAllocCount + totalFree := consStats.largeFree + nFree := consStats.largeFreeCount + + // Collect per-sizeclass stats. + var bySize [_NumSizeClasses]struct { + Size uint32 + Mallocs uint64 + Frees uint64 + } + for i := range bySize { + bySize[i].Size = uint32(class_to_size[i]) + + // Malloc stats. + a := consStats.smallAllocCount[i] + totalAlloc += a * uint64(class_to_size[i]) + nMalloc += a + bySize[i].Mallocs = a + + // Free stats. + f := consStats.smallFreeCount[i] + totalFree += f * uint64(class_to_size[i]) + nFree += f + bySize[i].Frees = f + } + + // Account for tiny allocations. + // For historical reasons, MemStats includes tiny allocations + // in both the total free and total alloc count. This double-counts + // memory in some sense because their tiny allocation block is also + // counted. Tracking the lifetime of individual tiny allocations is + // currently not done because it would be too expensive. + nFree += consStats.tinyAllocCount + nMalloc += consStats.tinyAllocCount + + // Calculate derived stats. + + stackInUse := uint64(consStats.inStacks) + gcWorkBufInUse := uint64(consStats.inWorkBufs) + gcProgPtrScalarBitsInUse := uint64(consStats.inPtrScalarBits) + + totalMapped := gcController.heapInUse.load() + gcController.heapFree.load() + gcController.heapReleased.load() + + memstats.stacks_sys.load() + memstats.mspan_sys.load() + memstats.mcache_sys.load() + + memstats.buckhash_sys.load() + memstats.gcMiscSys.load() + memstats.other_sys.load() + + stackInUse + gcWorkBufInUse + gcProgPtrScalarBitsInUse + + heapGoal := gcController.heapGoal() + + if doubleCheckReadMemStats { + // Only check this if we're debugging. It would be bad to crash an application + // just because the debugging stats are wrong. We mostly rely on tests to catch + // these issues, and we enable the double check mode for tests. + // + // The world is stopped, so the consistent stats (after aggregation) + // should be identical to some combination of memstats. In particular: + // + // * memstats.heapInUse == inHeap + // * memstats.heapReleased == released + // * memstats.heapInUse + memstats.heapFree == committed - inStacks - inWorkBufs - inPtrScalarBits + // * memstats.totalAlloc == totalAlloc + // * memstats.totalFree == totalFree + // + // Check if that's actually true. + // + // Prevent sysmon and the tracer from skewing the stats since they can + // act without synchronizing with a STW. See #64401. + lock(&sched.sysmonlock) + lock(&trace.lock) + if gcController.heapInUse.load() != uint64(consStats.inHeap) { + print("runtime: heapInUse=", gcController.heapInUse.load(), "\n") + print("runtime: consistent value=", consStats.inHeap, "\n") + throw("heapInUse and consistent stats are not equal") + } + if gcController.heapReleased.load() != uint64(consStats.released) { + print("runtime: heapReleased=", gcController.heapReleased.load(), "\n") + print("runtime: consistent value=", consStats.released, "\n") + throw("heapReleased and consistent stats are not equal") + } + heapRetained := gcController.heapInUse.load() + gcController.heapFree.load() + consRetained := uint64(consStats.committed - consStats.inStacks - consStats.inWorkBufs - consStats.inPtrScalarBits) + if heapRetained != consRetained { + print("runtime: global value=", heapRetained, "\n") + print("runtime: consistent value=", consRetained, "\n") + throw("measures of the retained heap are not equal") + } + if gcController.totalAlloc.Load() != totalAlloc { + print("runtime: totalAlloc=", gcController.totalAlloc.Load(), "\n") + print("runtime: consistent value=", totalAlloc, "\n") + throw("totalAlloc and consistent stats are not equal") + } + if gcController.totalFree.Load() != totalFree { + print("runtime: totalFree=", gcController.totalFree.Load(), "\n") + print("runtime: consistent value=", totalFree, "\n") + throw("totalFree and consistent stats are not equal") + } + // Also check that mappedReady lines up with totalMapped - released. + // This isn't really the same type of "make sure consistent stats line up" situation, + // but this is an opportune time to check. + if gcController.mappedReady.Load() != totalMapped-uint64(consStats.released) { + print("runtime: mappedReady=", gcController.mappedReady.Load(), "\n") + print("runtime: totalMapped=", totalMapped, "\n") + print("runtime: released=", uint64(consStats.released), "\n") + print("runtime: totalMapped-released=", totalMapped-uint64(consStats.released), "\n") + throw("mappedReady and other memstats are not equal") + } + unlock(&trace.lock) + unlock(&sched.sysmonlock) + } + + // We've calculated all the values we need. Now, populate stats. + + stats.Alloc = totalAlloc - totalFree + stats.TotalAlloc = totalAlloc + stats.Sys = totalMapped + stats.Mallocs = nMalloc + stats.Frees = nFree + stats.HeapAlloc = totalAlloc - totalFree + stats.HeapSys = gcController.heapInUse.load() + gcController.heapFree.load() + gcController.heapReleased.load() + // By definition, HeapIdle is memory that was mapped + // for the heap but is not currently used to hold heap + // objects. It also specifically is memory that can be + // used for other purposes, like stacks, but this memory + // is subtracted out of HeapSys before it makes that + // transition. Put another way: + // + // HeapSys = bytes allocated from the OS for the heap - bytes ultimately used for non-heap purposes + // HeapIdle = bytes allocated from the OS for the heap - bytes ultimately used for any purpose + // + // or + // + // HeapSys = sys - stacks_inuse - gcWorkBufInUse - gcProgPtrScalarBitsInUse + // HeapIdle = sys - stacks_inuse - gcWorkBufInUse - gcProgPtrScalarBitsInUse - heapInUse + // + // => HeapIdle = HeapSys - heapInUse = heapFree + heapReleased + stats.HeapIdle = gcController.heapFree.load() + gcController.heapReleased.load() + stats.HeapInuse = gcController.heapInUse.load() + stats.HeapReleased = gcController.heapReleased.load() + stats.HeapObjects = nMalloc - nFree + stats.StackInuse = stackInUse + // memstats.stacks_sys is only memory mapped directly for OS stacks. + // Add in heap-allocated stack memory for user consumption. + stats.StackSys = stackInUse + memstats.stacks_sys.load() + stats.MSpanInuse = uint64(mheap_.spanalloc.inuse) + stats.MSpanSys = memstats.mspan_sys.load() + stats.MCacheInuse = uint64(mheap_.cachealloc.inuse) + stats.MCacheSys = memstats.mcache_sys.load() + stats.BuckHashSys = memstats.buckhash_sys.load() + // MemStats defines GCSys as an aggregate of all memory related + // to the memory management system, but we track this memory + // at a more granular level in the runtime. + stats.GCSys = memstats.gcMiscSys.load() + gcWorkBufInUse + gcProgPtrScalarBitsInUse + stats.OtherSys = memstats.other_sys.load() + stats.NextGC = heapGoal + stats.LastGC = memstats.last_gc_unix + stats.PauseTotalNs = memstats.pause_total_ns + stats.PauseNs = memstats.pause_ns + stats.PauseEnd = memstats.pause_end + stats.NumGC = memstats.numgc + stats.NumForcedGC = memstats.numforcedgc + stats.GCCPUFraction = memstats.gc_cpu_fraction + stats.EnableGC = true + + // stats.BySize and bySize might not match in length. + // That's OK, stats.BySize cannot change due to backwards + // compatibility issues. copy will copy the minimum amount + // of values between the two of them. + copy(stats.BySize[:], bySize[:]) +} + +//go:linkname readGCStats runtime/debug.readGCStats +func readGCStats(pauses *[]uint64) { + systemstack(func() { + readGCStats_m(pauses) + }) +} + +// readGCStats_m must be called on the system stack because it acquires the heap +// lock. See mheap for details. +// +//go:systemstack +func readGCStats_m(pauses *[]uint64) { + p := *pauses + // Calling code in runtime/debug should make the slice large enough. + if cap(p) < len(memstats.pause_ns)+3 { + throw("short slice passed to readGCStats") + } + + // Pass back: pauses, pause ends, last gc (absolute time), number of gc, total pause ns. + lock(&mheap_.lock) + + n := memstats.numgc + if n > uint32(len(memstats.pause_ns)) { + n = uint32(len(memstats.pause_ns)) + } + + // The pause buffer is circular. The most recent pause is at + // pause_ns[(numgc-1)%len(pause_ns)], and then backward + // from there to go back farther in time. We deliver the times + // most recent first (in p[0]). + p = p[:cap(p)] + for i := uint32(0); i < n; i++ { + j := (memstats.numgc - 1 - i) % uint32(len(memstats.pause_ns)) + p[i] = memstats.pause_ns[j] + p[n+i] = memstats.pause_end[j] + } + + p[n+n] = memstats.last_gc_unix + p[n+n+1] = uint64(memstats.numgc) + p[n+n+2] = memstats.pause_total_ns + unlock(&mheap_.lock) + *pauses = p[:n+n+3] +} + +// flushmcache flushes the mcache of allp[i]. +// +// The world must be stopped. +// +//go:nowritebarrier +func flushmcache(i int) { + assertWorldStopped() + + p := allp[i] + c := p.mcache + if c == nil { + return + } + c.releaseAll() + stackcache_clear(c) +} + +// flushallmcaches flushes the mcaches of all Ps. +// +// The world must be stopped. +// +//go:nowritebarrier +func flushallmcaches() { + assertWorldStopped() + + for i := 0; i < int(gomaxprocs); i++ { + flushmcache(i) + } +} + +// sysMemStat represents a global system statistic that is managed atomically. +// +// This type must structurally be a uint64 so that mstats aligns with MemStats. +type sysMemStat uint64 + +// load atomically reads the value of the stat. +// +// Must be nosplit as it is called in runtime initialization, e.g. newosproc0. +// +//go:nosplit +func (s *sysMemStat) load() uint64 { + return atomic.Load64((*uint64)(s)) +} + +// add atomically adds the sysMemStat by n. +// +// Must be nosplit as it is called in runtime initialization, e.g. newosproc0. +// +//go:nosplit +func (s *sysMemStat) add(n int64) { + val := atomic.Xadd64((*uint64)(s), n) + if (n > 0 && int64(val) < n) || (n < 0 && int64(val)+n < n) { + print("runtime: val=", val, " n=", n, "\n") + throw("sysMemStat overflow") + } +} + +// heapStatsDelta contains deltas of various runtime memory statistics +// that need to be updated together in order for them to be kept +// consistent with one another. +type heapStatsDelta struct { + // Memory stats. + committed int64 // byte delta of memory committed + released int64 // byte delta of released memory generated + inHeap int64 // byte delta of memory placed in the heap + inStacks int64 // byte delta of memory reserved for stacks + inWorkBufs int64 // byte delta of memory reserved for work bufs + inPtrScalarBits int64 // byte delta of memory reserved for unrolled GC prog bits + + // Allocator stats. + // + // These are all uint64 because they're cumulative, and could quickly wrap + // around otherwise. + tinyAllocCount uint64 // number of tiny allocations + largeAlloc uint64 // bytes allocated for large objects + largeAllocCount uint64 // number of large object allocations + smallAllocCount [_NumSizeClasses]uint64 // number of allocs for small objects + largeFree uint64 // bytes freed for large objects (>maxSmallSize) + largeFreeCount uint64 // number of frees for large objects (>maxSmallSize) + smallFreeCount [_NumSizeClasses]uint64 // number of frees for small objects (<=maxSmallSize) + + // NOTE: This struct must be a multiple of 8 bytes in size because it + // is stored in an array. If it's not, atomic accesses to the above + // fields may be unaligned and fail on 32-bit platforms. +} + +// merge adds in the deltas from b into a. +func (a *heapStatsDelta) merge(b *heapStatsDelta) { + a.committed += b.committed + a.released += b.released + a.inHeap += b.inHeap + a.inStacks += b.inStacks + a.inWorkBufs += b.inWorkBufs + a.inPtrScalarBits += b.inPtrScalarBits + + a.tinyAllocCount += b.tinyAllocCount + a.largeAlloc += b.largeAlloc + a.largeAllocCount += b.largeAllocCount + for i := range b.smallAllocCount { + a.smallAllocCount[i] += b.smallAllocCount[i] + } + a.largeFree += b.largeFree + a.largeFreeCount += b.largeFreeCount + for i := range b.smallFreeCount { + a.smallFreeCount[i] += b.smallFreeCount[i] + } +} + +// consistentHeapStats represents a set of various memory statistics +// whose updates must be viewed completely to get a consistent +// state of the world. +// +// To write updates to memory stats use the acquire and release +// methods. To obtain a consistent global snapshot of these statistics, +// use read. +type consistentHeapStats struct { + // stats is a ring buffer of heapStatsDelta values. + // Writers always atomically update the delta at index gen. + // + // Readers operate by rotating gen (0 -> 1 -> 2 -> 0 -> ...) + // and synchronizing with writers by observing each P's + // statsSeq field. If the reader observes a P not writing, + // it can be sure that it will pick up the new gen value the + // next time it writes. + // + // The reader then takes responsibility by clearing space + // in the ring buffer for the next reader to rotate gen to + // that space (i.e. it merges in values from index (gen-2) mod 3 + // to index (gen-1) mod 3, then clears the former). + // + // Note that this means only one reader can be reading at a time. + // There is no way for readers to synchronize. + // + // This process is why we need a ring buffer of size 3 instead + // of 2: one is for the writers, one contains the most recent + // data, and the last one is clear so writers can begin writing + // to it the moment gen is updated. + stats [3]heapStatsDelta + + // gen represents the current index into which writers + // are writing, and can take on the value of 0, 1, or 2. + gen atomic.Uint32 + + // noPLock is intended to provide mutual exclusion for updating + // stats when no P is available. It does not block other writers + // with a P, only other writers without a P and the reader. Because + // stats are usually updated when a P is available, contention on + // this lock should be minimal. + noPLock mutex +} + +// acquire returns a heapStatsDelta to be updated. In effect, +// it acquires the shard for writing. release must be called +// as soon as the relevant deltas are updated. +// +// The returned heapStatsDelta must be updated atomically. +// +// The caller's P must not change between acquire and +// release. This also means that the caller should not +// acquire a P or release its P in between. A P also must +// not acquire a given consistentHeapStats if it hasn't +// yet released it. +// +// nosplit because a stack growth in this function could +// lead to a stack allocation that could reenter the +// function. +// +//go:nosplit +func (m *consistentHeapStats) acquire() *heapStatsDelta { + if pp := getg().m.p.ptr(); pp != nil { + seq := pp.statsSeq.Add(1) + if seq%2 == 0 { + // Should have been incremented to odd. + print("runtime: seq=", seq, "\n") + throw("bad sequence number") + } + } else { + lock(&m.noPLock) + } + gen := m.gen.Load() % 3 + return &m.stats[gen] +} + +// release indicates that the writer is done modifying +// the delta. The value returned by the corresponding +// acquire must no longer be accessed or modified after +// release is called. +// +// The caller's P must not change between acquire and +// release. This also means that the caller should not +// acquire a P or release its P in between. +// +// nosplit because a stack growth in this function could +// lead to a stack allocation that causes another acquire +// before this operation has completed. +// +//go:nosplit +func (m *consistentHeapStats) release() { + if pp := getg().m.p.ptr(); pp != nil { + seq := pp.statsSeq.Add(1) + if seq%2 != 0 { + // Should have been incremented to even. + print("runtime: seq=", seq, "\n") + throw("bad sequence number") + } + } else { + unlock(&m.noPLock) + } +} + +// unsafeRead aggregates the delta for this shard into out. +// +// Unsafe because it does so without any synchronization. The +// world must be stopped. +func (m *consistentHeapStats) unsafeRead(out *heapStatsDelta) { + assertWorldStopped() + + for i := range m.stats { + out.merge(&m.stats[i]) + } +} + +// unsafeClear clears the shard. +// +// Unsafe because the world must be stopped and values should +// be donated elsewhere before clearing. +func (m *consistentHeapStats) unsafeClear() { + assertWorldStopped() + + for i := range m.stats { + m.stats[i] = heapStatsDelta{} + } +} + +// read takes a globally consistent snapshot of m +// and puts the aggregated value in out. Even though out is a +// heapStatsDelta, the resulting values should be complete and +// valid statistic values. +// +// Not safe to call concurrently. The world must be stopped +// or metricsSema must be held. +func (m *consistentHeapStats) read(out *heapStatsDelta) { + // Getting preempted after this point is not safe because + // we read allp. We need to make sure a STW can't happen + // so it doesn't change out from under us. + mp := acquirem() + + // Get the current generation. We can be confident that this + // will not change since read is serialized and is the only + // one that modifies currGen. + currGen := m.gen.Load() + prevGen := currGen - 1 + if currGen == 0 { + prevGen = 2 + } + + // Prevent writers without a P from writing while we update gen. + lock(&m.noPLock) + + // Rotate gen, effectively taking a snapshot of the state of + // these statistics at the point of the exchange by moving + // writers to the next set of deltas. + // + // This exchange is safe to do because we won't race + // with anyone else trying to update this value. + m.gen.Swap((currGen + 1) % 3) + + // Allow P-less writers to continue. They'll be writing to the + // next generation now. + unlock(&m.noPLock) + + for _, p := range allp { + // Spin until there are no more writers. + for p.statsSeq.Load()%2 != 0 { + } + } + + // At this point we've observed that each sequence + // number is even, so any future writers will observe + // the new gen value. That means it's safe to read from + // the other deltas in the stats buffer. + + // Perform our responsibilities and free up + // stats[prevGen] for the next time we want to take + // a snapshot. + m.stats[currGen].merge(&m.stats[prevGen]) + m.stats[prevGen] = heapStatsDelta{} + + // Finally, copy out the complete delta. + *out = m.stats[currGen] + + releasem(mp) +} + +type cpuStats struct { + // All fields are CPU time in nanoseconds computed by comparing + // calls of nanotime. This means they're all overestimates, because + // they don't accurately compute on-CPU time (so some of the time + // could be spent scheduled away by the OS). + + gcAssistTime int64 // GC assists + gcDedicatedTime int64 // GC dedicated mark workers + pauses + gcIdleTime int64 // GC idle mark workers + gcPauseTime int64 // GC pauses (all GOMAXPROCS, even if just 1 is running) + gcTotalTime int64 + + scavengeAssistTime int64 // background scavenger + scavengeBgTime int64 // scavenge assists + scavengeTotalTime int64 + + idleTime int64 // Time Ps spent in _Pidle. + userTime int64 // Time Ps spent in _Prunning or _Psyscall that's not any of the above. + + totalTime int64 // GOMAXPROCS * (monotonic wall clock time elapsed) +} + +// accumulate takes a cpuStats and adds in the current state of all GC CPU +// counters. +// +// gcMarkPhase indicates that we're in the mark phase and that certain counter +// values should be used. +func (s *cpuStats) accumulate(now int64, gcMarkPhase bool) { + // N.B. Mark termination and sweep termination pauses are + // accumulated in work.cpuStats at the end of their respective pauses. + var ( + markAssistCpu int64 + markDedicatedCpu int64 + markFractionalCpu int64 + markIdleCpu int64 + ) + if gcMarkPhase { + // N.B. These stats may have stale values if the GC is not + // currently in the mark phase. + markAssistCpu = gcController.assistTime.Load() + markDedicatedCpu = gcController.dedicatedMarkTime.Load() + markFractionalCpu = gcController.fractionalMarkTime.Load() + markIdleCpu = gcController.idleMarkTime.Load() + } + + // The rest of the stats below are either derived from the above or + // are reset on each mark termination. + + scavAssistCpu := scavenge.assistTime.Load() + scavBgCpu := scavenge.backgroundTime.Load() + + // Update cumulative GC CPU stats. + s.gcAssistTime += markAssistCpu + s.gcDedicatedTime += markDedicatedCpu + markFractionalCpu + s.gcIdleTime += markIdleCpu + s.gcTotalTime += markAssistCpu + markDedicatedCpu + markFractionalCpu + markIdleCpu + + // Update cumulative scavenge CPU stats. + s.scavengeAssistTime += scavAssistCpu + s.scavengeBgTime += scavBgCpu + s.scavengeTotalTime += scavAssistCpu + scavBgCpu + + // Update total CPU. + s.totalTime = sched.totaltime + (now-sched.procresizetime)*int64(gomaxprocs) + s.idleTime += sched.idleTime.Load() + + // Compute userTime. We compute this indirectly as everything that's not the above. + // + // Since time spent in _Pgcstop is covered by gcPauseTime, and time spent in _Pidle + // is covered by idleTime, what we're left with is time spent in _Prunning and _Psyscall, + // the latter of which is fine because the P will either go idle or get used for something + // else via sysmon. Meanwhile if we subtract GC time from whatever's left, we get non-GC + // _Prunning time. Note that this still leaves time spent in sweeping and in the scheduler, + // but that's fine. The overwhelming majority of this time will be actual user time. + s.userTime = s.totalTime - (s.gcTotalTime + s.scavengeTotalTime + s.idleTime) +} |