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Factor trace deque out to shared-worklist.h
Also increase alignment to account for cache line prefetcher.
This commit is contained in:
Andy Wingo
parent
b4bf949df6
commit
dd3953ef1a
3 changed files with 280 additions and 255 deletions
259
src/shared-worklist.h
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259
src/shared-worklist.h
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#ifndef SHARED_WORKLIST_H
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#define SHARED_WORKLIST_H
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#include <stdatomic.h>
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#include <sys/mman.h>
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#include <unistd.h>
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#include "assert.h"
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#include "debug.h"
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#include "gc-align.h"
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#include "gc-inline.h"
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#include "spin.h"
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// The Chase-Lev work-stealing deque, as initially described in "Dynamic
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// Circular Work-Stealing Deque" (Chase and Lev, SPAA'05)
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// (https://www.dre.vanderbilt.edu/~schmidt/PDF/work-stealing-dequeue.pdf)
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// and improved with C11 atomics in "Correct and Efficient Work-Stealing
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// for Weak Memory Models" (Lê et al, PPoPP'13)
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// (http://www.di.ens.fr/%7Ezappa/readings/ppopp13.pdf).
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struct shared_worklist_buf {
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unsigned log_size;
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size_t size;
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uintptr_t *data;
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};
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// Min size: 8 kB on 64-bit systems, 4 kB on 32-bit.
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#define shared_worklist_buf_min_log_size ((unsigned) 10)
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// Max size: 2 GB on 64-bit systems, 1 GB on 32-bit.
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#define shared_worklist_buf_max_log_size ((unsigned) 28)
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static int
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shared_worklist_buf_init(struct shared_worklist_buf *buf, unsigned log_size) {
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ASSERT(log_size >= shared_worklist_buf_min_log_size);
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ASSERT(log_size <= shared_worklist_buf_max_log_size);
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size_t size = (1 << log_size) * sizeof(uintptr_t);
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void *mem = mmap(NULL, size, PROT_READ|PROT_WRITE,
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MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
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if (mem == MAP_FAILED) {
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perror("Failed to grow work-stealing dequeue");
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DEBUG("Failed to allocate %zu bytes", size);
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return 0;
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}
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buf->log_size = log_size;
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buf->size = 1 << log_size;
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buf->data = mem;
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return 1;
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}
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static inline size_t
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shared_worklist_buf_size(struct shared_worklist_buf *buf) {
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return buf->size;
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}
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static inline size_t
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shared_worklist_buf_byte_size(struct shared_worklist_buf *buf) {
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return shared_worklist_buf_size(buf) * sizeof(uintptr_t);
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}
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static void
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shared_worklist_buf_release(struct shared_worklist_buf *buf) {
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if (buf->data)
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madvise(buf->data, shared_worklist_buf_byte_size(buf), MADV_DONTNEED);
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}
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static void
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shared_worklist_buf_destroy(struct shared_worklist_buf *buf) {
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if (buf->data) {
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munmap(buf->data, shared_worklist_buf_byte_size(buf));
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buf->data = NULL;
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buf->log_size = 0;
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buf->size = 0;
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}
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}
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static inline struct gc_ref
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shared_worklist_buf_get(struct shared_worklist_buf *buf, size_t i) {
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return gc_ref(atomic_load_explicit(&buf->data[i & (buf->size - 1)],
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memory_order_relaxed));
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}
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static inline void
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shared_worklist_buf_put(struct shared_worklist_buf *buf, size_t i,
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struct gc_ref ref) {
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return atomic_store_explicit(&buf->data[i & (buf->size - 1)],
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gc_ref_value(ref),
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memory_order_relaxed);
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}
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static inline int
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shared_worklist_buf_grow(struct shared_worklist_buf *from,
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struct shared_worklist_buf *to, size_t b, size_t t) {
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if (from->log_size == shared_worklist_buf_max_log_size)
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return 0;
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if (!shared_worklist_buf_init (to, from->log_size + 1))
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return 0;
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for (size_t i=t; i<b; i++)
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shared_worklist_buf_put(to, i, shared_worklist_buf_get(from, i));
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return 1;
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}
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// Chase-Lev work-stealing deque. One thread pushes data into the deque
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// at the bottom, and many threads compete to steal data from the top.
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struct shared_worklist {
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// Ensure bottom and top are on different cache lines.
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union {
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atomic_size_t bottom;
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char bottom_padding[AVOID_FALSE_SHARING];
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};
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union {
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atomic_size_t top;
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char top_padding[AVOID_FALSE_SHARING];
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};
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atomic_int active; // Which shared_worklist_buf is active.
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struct shared_worklist_buf bufs[(shared_worklist_buf_max_log_size -
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shared_worklist_buf_min_log_size) + 1];
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};
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#define LOAD_RELAXED(loc) atomic_load_explicit(loc, memory_order_relaxed)
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#define STORE_RELAXED(loc, o) atomic_store_explicit(loc, o, memory_order_relaxed)
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#define LOAD_ACQUIRE(loc) atomic_load_explicit(loc, memory_order_acquire)
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#define STORE_RELEASE(loc, o) atomic_store_explicit(loc, o, memory_order_release)
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#define LOAD_CONSUME(loc) atomic_load_explicit(loc, memory_order_consume)
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static int
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shared_worklist_init(struct shared_worklist *q) {
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memset(q, 0, sizeof (*q));
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int ret = shared_worklist_buf_init(&q->bufs[0],
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shared_worklist_buf_min_log_size);
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// Note, this fence isn't in the paper, I added it out of caution.
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atomic_thread_fence(memory_order_release);
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return ret;
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}
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static void
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shared_worklist_release(struct shared_worklist *q) {
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for (int i = LOAD_RELAXED(&q->active); i >= 0; i--)
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shared_worklist_buf_release(&q->bufs[i]);
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}
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static void
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shared_worklist_destroy(struct shared_worklist *q) {
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for (int i = LOAD_RELAXED(&q->active); i >= 0; i--)
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shared_worklist_buf_destroy(&q->bufs[i]);
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}
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static int
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shared_worklist_grow(struct shared_worklist *q, int cur, size_t b, size_t t) {
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if (!shared_worklist_buf_grow(&q->bufs[cur], &q->bufs[cur + 1], b, t)) {
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fprintf(stderr, "failed to grow deque!!\n");
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GC_CRASH();
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}
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cur++;
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STORE_RELAXED(&q->active, cur);
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return cur;
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}
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static void
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shared_worklist_push(struct shared_worklist *q, struct gc_ref x) {
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size_t b = LOAD_RELAXED(&q->bottom);
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size_t t = LOAD_ACQUIRE(&q->top);
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int active = LOAD_RELAXED(&q->active);
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ssize_t size = b - t;
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if (size > shared_worklist_buf_size(&q->bufs[active]) - 1)
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active = shared_worklist_grow(q, active, b, t); /* Full queue; grow. */
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shared_worklist_buf_put(&q->bufs[active], b, x);
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atomic_thread_fence(memory_order_release);
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STORE_RELAXED(&q->bottom, b + 1);
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}
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static void
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shared_worklist_push_many(struct shared_worklist *q, struct gc_ref *objv,
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size_t count) {
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size_t b = LOAD_RELAXED(&q->bottom);
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size_t t = LOAD_ACQUIRE(&q->top);
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int active = LOAD_RELAXED(&q->active);
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ssize_t size = b - t;
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while (size > shared_worklist_buf_size(&q->bufs[active]) - count)
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active = shared_worklist_grow(q, active, b, t); /* Full queue; grow. */
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for (size_t i = 0; i < count; i++)
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shared_worklist_buf_put(&q->bufs[active], b + i, objv[i]);
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atomic_thread_fence(memory_order_release);
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STORE_RELAXED(&q->bottom, b + count);
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}
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static struct gc_ref
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shared_worklist_try_pop(struct shared_worklist *q) {
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size_t b = LOAD_RELAXED(&q->bottom);
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int active = LOAD_RELAXED(&q->active);
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STORE_RELAXED(&q->bottom, b - 1);
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atomic_thread_fence(memory_order_seq_cst);
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size_t t = LOAD_RELAXED(&q->top);
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struct gc_ref x;
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ssize_t size = b - t;
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if (size > 0) { // Non-empty queue.
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x = shared_worklist_buf_get(&q->bufs[active], b - 1);
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if (size == 1) { // Single last element in queue.
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if (!atomic_compare_exchange_strong_explicit(&q->top, &t, t + 1,
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memory_order_seq_cst,
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memory_order_relaxed))
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// Failed race.
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x = gc_ref_null();
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STORE_RELAXED(&q->bottom, b);
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}
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} else { // Empty queue.
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x = gc_ref_null();
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STORE_RELAXED(&q->bottom, b);
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}
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return x;
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}
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static struct gc_ref
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shared_worklist_steal(struct shared_worklist *q) {
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while (1) {
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size_t t = LOAD_ACQUIRE(&q->top);
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atomic_thread_fence(memory_order_seq_cst);
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size_t b = LOAD_ACQUIRE(&q->bottom);
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ssize_t size = b - t;
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if (size <= 0)
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return gc_ref_null();
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int active = LOAD_CONSUME(&q->active);
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struct gc_ref ref = shared_worklist_buf_get(&q->bufs[active], t);
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if (!atomic_compare_exchange_strong_explicit(&q->top, &t, t + 1,
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memory_order_seq_cst,
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memory_order_relaxed))
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// Failed race.
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continue;
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return ref;
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}
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}
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static ssize_t
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shared_worklist_size(struct shared_worklist *q) {
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size_t t = LOAD_ACQUIRE(&q->top);
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atomic_thread_fence(memory_order_seq_cst);
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size_t b = LOAD_ACQUIRE(&q->bottom);
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ssize_t size = b - t;
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return size;
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}
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static int
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shared_worklist_can_steal(struct shared_worklist *q) {
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return shared_worklist_size(q) > 0;
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}
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#undef LOAD_RELAXED
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#undef STORE_RELAXED
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#undef LOAD_ACQUIRE
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#undef STORE_RELEASE
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#undef LOAD_CONSUME
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#endif // SHARED_WORKLIST_H
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