Revision f442e4230a41d0d40f81346c1707f946f743cbcf authored by Jeff Bezanson on 09 June 2021, 02:51:34 UTC, committed by GitHub on 09 June 2021, 02:51:34 UTC
This PR implements a way to keep tables of methods that are not part of the internal method table, but still participate in the special support we have for keeping tables of methods, in particular unification through precompilation and efficient lookup. The intended design use case is to allow for method overlay tables for various non-CPU backends (e.g. GPU and TPU). These backends would like to modify basic function like `sin` to perform better on the device in question (or in the case of TPU to define them over non-LLVM intrinsics). It is worth noting that this PR only gives the ability to keep these tables of methods. It assigns no particular meaning to them and the runtime (and regular inference) do not look at them. They are designed as an implementation detail for external compilers and similar tools. # Demo ```julia julia> using Base.Experimental: @overlay, @MethodTable julia> @MethodTable(mt) # 0 methods: julia> @overlay mt function sin(x::Float64) 1 end julia> @overlay mt function cos(x::Float64) 1 end julia> mt # 2 methods: [1] cos(x::Float64) in Main at REPL[5]:1 [2] sin(x::Float64) in Main at REPL[4]:1 julia> Base._methods_by_ftype(Tuple{typeof(sin), Float64}, mt, 1, typemax(UInt)) 1-element Vector{Any}: Core.MethodMatch(Tuple{typeof(sin), Float64}, svec(), sin(x::Float64) in Main at REPL[4]:1, true) julia> Base._methods_by_ftype(Tuple{typeof(sin), Float64}, 1, typemax(UInt)) 1-element Vector{Any}: Core.MethodMatch(Tuple{typeof(sin), Float64}, svec(Float64), sin(x::T) where T<:Union{Float32, Float64} in Base.Math at special/trig.jl:29, true) ``` Co-authored-by: Tim Besard <tim.besard@gmail.com> Co-authored-by: Julian P Samaroo <jpsamaroo@jpsamaroo.me> Co-authored-by: Keno Fischer <keno@juliacomputing.com>
1 parent 0e3276c
partr.c
// This file is a part of Julia. License is MIT: https://julialang.org/license
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include "julia.h"
#include "julia_internal.h"
#include "gc.h"
#include "threading.h"
#ifdef __cplusplus
extern "C" {
#endif
// thread sleep state
// thread should not be sleeping--it might need to do work.
static const int16_t not_sleeping = 0;
// it is acceptable for the thread to be sleeping.
static const int16_t sleeping = 1;
// invariant: No thread is ever asleep unless sleep_check_state is sleeping (or we have a wakeup signal pending).
// invariant: Any particular thread is not asleep unless that thread's sleep_check_state is sleeping.
// invariant: The transition of a thread state to sleeping must be followed by a check that there wasn't work pending for it.
// information: Observing thread not-sleeping is sufficient to ensure the target thread will subsequently inspect its local queue.
// information: Observing thread is-sleeping says it may be necessary to notify it at least once to wakeup. It may already be awake however for a variety of reasons.
JULIA_DEBUG_SLEEPWAKE(
uint64_t wakeup_enter;
uint64_t wakeup_leave;
uint64_t io_wakeup_enter;
uint64_t io_wakeup_leave;
);
JL_DLLEXPORT int jl_set_task_tid(jl_task_t *task, int tid) JL_NOTSAFEPOINT
{
// Try to acquire the lock on this task.
int16_t was = jl_atomic_load_relaxed(&task->tid);
if (was == tid)
return 1;
if (was == -1)
return jl_atomic_cmpswap(&task->tid, &was, tid);
return 0;
}
// GC functions used
extern int jl_gc_mark_queue_obj_explicit(jl_gc_mark_cache_t *gc_cache,
jl_gc_mark_sp_t *sp, jl_value_t *obj) JL_NOTSAFEPOINT;
// multiq
// ---
/* a task heap */
typedef struct taskheap_tag {
jl_mutex_t lock;
jl_task_t **tasks;
int32_t ntasks;
int16_t prio;
} taskheap_t;
/* multiqueue parameters */
static const int32_t heap_d = 8;
static const int heap_c = 2;
/* size of each heap */
static const int tasks_per_heap = 65536; // TODO: this should be smaller by default, but growable!
/* the multiqueue's heaps */
static taskheap_t *heaps;
static int32_t heap_p;
/* unbias state for the RNG */
static uint64_t cong_unbias;
static inline void multiq_init(void)
{
heap_p = heap_c * jl_n_threads;
heaps = (taskheap_t *)calloc(heap_p, sizeof(taskheap_t));
for (int32_t i = 0; i < heap_p; ++i) {
jl_mutex_init(&heaps[i].lock);
heaps[i].tasks = (jl_task_t **)calloc(tasks_per_heap, sizeof(jl_task_t*));
heaps[i].ntasks = 0;
heaps[i].prio = INT16_MAX;
}
unbias_cong(heap_p, &cong_unbias);
}
static inline void sift_up(taskheap_t *heap, int32_t idx)
{
if (idx > 0) {
int32_t parent = (idx-1)/heap_d;
if (heap->tasks[idx]->prio < heap->tasks[parent]->prio) {
jl_task_t *t = heap->tasks[parent];
heap->tasks[parent] = heap->tasks[idx];
heap->tasks[idx] = t;
sift_up(heap, parent);
}
}
}
static inline void sift_down(taskheap_t *heap, int32_t idx)
{
if (idx < heap->ntasks) {
for (int32_t child = heap_d*idx + 1;
child < tasks_per_heap && child <= heap_d*idx + heap_d;
++child) {
if (heap->tasks[child]
&& heap->tasks[child]->prio < heap->tasks[idx]->prio) {
jl_task_t *t = heap->tasks[idx];
heap->tasks[idx] = heap->tasks[child];
heap->tasks[child] = t;
sift_down(heap, child);
}
}
}
}
static inline int multiq_insert(jl_task_t *task, int16_t priority)
{
jl_ptls_t ptls = jl_current_task->ptls;
uint64_t rn;
task->prio = priority;
do {
rn = cong(heap_p, cong_unbias, &ptls->rngseed);
} while (!jl_mutex_trylock_nogc(&heaps[rn].lock));
if (heaps[rn].ntasks >= tasks_per_heap) {
jl_mutex_unlock_nogc(&heaps[rn].lock);
// multiq insertion failed, increase #tasks per heap
return -1;
}
heaps[rn].tasks[heaps[rn].ntasks++] = task;
sift_up(&heaps[rn], heaps[rn].ntasks-1);
int16_t prio = jl_atomic_load(&heaps[rn].prio);
if (task->prio < prio)
jl_atomic_store(&heaps[rn].prio, task->prio);
jl_mutex_unlock_nogc(&heaps[rn].lock);
return 0;
}
static inline jl_task_t *multiq_deletemin(void)
{
jl_ptls_t ptls = jl_current_task->ptls;
uint64_t rn1 = 0, rn2;
int32_t i;
int16_t prio1, prio2;
jl_task_t *task;
retry:
for (i = 0; i < heap_p; ++i) {
rn1 = cong(heap_p, cong_unbias, &ptls->rngseed);
rn2 = cong(heap_p, cong_unbias, &ptls->rngseed);
prio1 = jl_atomic_load(&heaps[rn1].prio);
prio2 = jl_atomic_load(&heaps[rn2].prio);
if (prio1 > prio2) {
prio1 = prio2;
rn1 = rn2;
}
else if (prio1 == prio2 && prio1 == INT16_MAX)
continue;
if (jl_mutex_trylock_nogc(&heaps[rn1].lock)) {
if (prio1 == heaps[rn1].prio)
break;
jl_mutex_unlock_nogc(&heaps[rn1].lock);
}
}
if (i == heap_p)
return NULL;
task = heaps[rn1].tasks[0];
if (!jl_set_task_tid(task, ptls->tid)) {
jl_mutex_unlock_nogc(&heaps[rn1].lock);
goto retry;
}
heaps[rn1].tasks[0] = heaps[rn1].tasks[--heaps[rn1].ntasks];
heaps[rn1].tasks[heaps[rn1].ntasks] = NULL;
prio1 = INT16_MAX;
if (heaps[rn1].ntasks > 0) {
sift_down(&heaps[rn1], 0);
prio1 = heaps[rn1].tasks[0]->prio;
}
jl_atomic_store(&heaps[rn1].prio, prio1);
jl_mutex_unlock_nogc(&heaps[rn1].lock);
return task;
}
void jl_gc_mark_enqueued_tasks(jl_gc_mark_cache_t *gc_cache, jl_gc_mark_sp_t *sp)
{
int32_t i, j;
for (i = 0; i < heap_p; ++i)
for (j = 0; j < heaps[i].ntasks; ++j)
jl_gc_mark_queue_obj_explicit(gc_cache, sp, (jl_value_t *)heaps[i].tasks[j]);
}
static int multiq_check_empty(void)
{
int32_t i;
for (i = 0; i < heap_p; ++i) {
if (heaps[i].ntasks != 0)
return 0;
}
return 1;
}
// parallel task runtime
// ---
// initialize the threading infrastructure
void jl_init_threadinginfra(void)
{
/* initialize the synchronization trees pool and the multiqueue */
multiq_init();
jl_ptls_t ptls = jl_current_task->ptls;
jl_install_thread_signal_handler(ptls);
uv_mutex_init(&ptls->sleep_lock);
uv_cond_init(&ptls->wake_signal);
}
void JL_NORETURN jl_finish_task(jl_task_t *t);
// thread function: used by all except the main thread
void jl_threadfun(void *arg)
{
jl_threadarg_t *targ = (jl_threadarg_t*)arg;
// initialize this thread (set tid, create heap, set up root task)
jl_ptls_t ptls = jl_init_threadtls(targ->tid);
void *stack_lo, *stack_hi;
jl_init_stack_limits(0, &stack_lo, &stack_hi);
jl_init_root_task(ptls, stack_lo, stack_hi);
jl_install_thread_signal_handler(ptls);
// set up sleep mechanism for this thread
uv_mutex_init(&ptls->sleep_lock);
uv_cond_init(&ptls->wake_signal);
// wait for all threads
jl_gc_state_set(ptls, JL_GC_STATE_SAFE, 0);
uv_barrier_wait(targ->barrier);
// free the thread argument here
free(targ);
(void)jl_gc_unsafe_enter(ptls);
jl_finish_task(jl_current_task); // noreturn
}
// enqueue the specified task for execution
JL_DLLEXPORT int jl_enqueue_task(jl_task_t *task)
{
if (multiq_insert(task, task->prio) == -1)
return 1;
return 0;
}
int jl_running_under_rr(int recheck)
{
#ifdef _OS_LINUX_
#define RR_CALL_BASE 1000
#define SYS_rrcall_check_presence (RR_CALL_BASE + 8)
static int checked_running_under_rr = 0;
static int is_running_under_rr = 0;
if (!checked_running_under_rr || recheck) {
int ret = syscall(SYS_rrcall_check_presence, 0, 0, 0, 0, 0, 0);
if (ret == -1) {
// Should always be ENOSYS, but who knows what people do for
// unknown syscalls with their seccomp filters, so just say
// that we don't have rr.
is_running_under_rr = 0;
}
else {
is_running_under_rr = 1;
}
checked_running_under_rr = 1;
}
return is_running_under_rr;
#else
return 0;
#endif
}
// sleep_check_after_threshold() -- if sleep_threshold ns have passed, return 1
static int sleep_check_after_threshold(uint64_t *start_cycles)
{
JULIA_DEBUG_SLEEPWAKE( return 1 ); // hammer on the sleep/wake logic much harder
/**
* This wait loop is a bit of a worst case for rr - it needs timer access,
* which are slow and it busy loops in user space, which prevents the
* scheduling logic from switching to other threads. Just don't bother
* trying to wait here
*/
if (jl_running_under_rr(0))
return 1;
if (!(*start_cycles)) {
*start_cycles = jl_hrtime();
return 0;
}
uint64_t elapsed_cycles = jl_hrtime() - (*start_cycles);
if (elapsed_cycles >= DEFAULT_THREAD_SLEEP_THRESHOLD) {
*start_cycles = 0;
return 1;
}
return 0;
}
static void wake_thread(int16_t tid)
{
jl_ptls_t other = jl_all_tls_states[tid];
uint8_t state = sleeping;
jl_atomic_cmpswap(&other->sleep_check_state, &state, not_sleeping);
if (state == sleeping) {
uv_mutex_lock(&other->sleep_lock);
uv_cond_signal(&other->wake_signal);
uv_mutex_unlock(&other->sleep_lock);
}
}
static void wake_libuv(void)
{
JULIA_DEBUG_SLEEPWAKE( io_wakeup_enter = cycleclock() );
jl_wake_libuv();
JULIA_DEBUG_SLEEPWAKE( io_wakeup_leave = cycleclock() );
}
/* ensure thread tid is awake if necessary */
JL_DLLEXPORT void jl_wakeup_thread(int16_t tid)
{
jl_ptls_t ptls = jl_current_task->ptls;
jl_thread_t uvlock = jl_atomic_load(&jl_uv_mutex.owner);
int16_t self = ptls->tid;
jl_thread_t system_self = jl_all_tls_states[self]->system_id;
JULIA_DEBUG_SLEEPWAKE( wakeup_enter = cycleclock() );
if (tid == self || tid == -1) {
// we're already awake, but make sure we'll exit uv_run
if (jl_atomic_load_relaxed(&ptls->sleep_check_state) == sleeping)
jl_atomic_store(&ptls->sleep_check_state, not_sleeping);
if (uvlock == system_self)
uv_stop(jl_global_event_loop());
}
else {
// something added to the sticky-queue: notify that thread
wake_thread(tid);
// check if we need to notify uv_run too
jl_thread_t system_tid = jl_all_tls_states[tid]->system_id;
if (uvlock != system_self && jl_atomic_load(&jl_uv_mutex.owner) == system_tid)
wake_libuv();
}
// check if the other threads might be sleeping
if (tid == -1) {
// something added to the multi-queue: notify all threads
// in the future, we might want to instead wake some fraction of threads,
// and let each of those wake additional threads if they find work
for (tid = 0; tid < jl_n_threads; tid++) {
if (tid != self)
wake_thread(tid);
}
// check if we need to notify uv_run too
if (uvlock != system_self && jl_atomic_load(&jl_uv_mutex.owner) != 0)
wake_libuv();
}
JULIA_DEBUG_SLEEPWAKE( wakeup_leave = cycleclock() );
}
// get the next runnable task from the multiq
static jl_task_t *get_next_task(jl_value_t *trypoptask, jl_value_t *q)
{
jl_gc_safepoint();
jl_value_t *args[2] = { trypoptask, q };
jl_task_t *task = (jl_task_t*)jl_apply(args, 2);
if (jl_typeis(task, jl_task_type)) {
int self = jl_current_task->tid;
jl_set_task_tid(task, self);
return task;
}
jl_gc_safepoint();
return multiq_deletemin();
}
static int may_sleep(jl_ptls_t ptls)
{
// sleep_check_state is only transitioned from not_sleeping to sleeping
// by the thread itself. As a result, if this returns false, it will
// continue returning false. If it returns true, there are no guarantees.
return jl_atomic_load_relaxed(&ptls->sleep_check_state) == sleeping;
}
extern volatile unsigned _threadedregion;
JL_DLLEXPORT jl_task_t *jl_task_get_next(jl_value_t *trypoptask, jl_value_t *q)
{
jl_task_t *ct = jl_current_task;
uint64_t start_cycles = 0;
while (1) {
jl_task_t *task = get_next_task(trypoptask, q);
if (task)
return task;
// quick, race-y check to see if there seems to be any stuff in there
jl_cpu_pause();
if (!multiq_check_empty()) {
start_cycles = 0;
continue;
}
jl_cpu_pause();
jl_ptls_t ptls = ct->ptls;
if (sleep_check_after_threshold(&start_cycles) || (!_threadedregion && ptls->tid == 0)) {
jl_atomic_store(&ptls->sleep_check_state, sleeping); // acquire sleep-check lock
if (!multiq_check_empty()) {
if (jl_atomic_load_relaxed(&ptls->sleep_check_state) != not_sleeping)
jl_atomic_store(&ptls->sleep_check_state, not_sleeping); // let other threads know they don't need to wake us
continue;
}
task = get_next_task(trypoptask, q); // WARNING: this should not yield
if (ptls != ct->ptls)
continue;
if (task) {
if (jl_atomic_load_relaxed(&ptls->sleep_check_state) != not_sleeping)
jl_atomic_store(&ptls->sleep_check_state, not_sleeping); // let other threads know they don't need to wake us
return task;
}
// one thread should win this race and watch the event loop
// inside a threaded region, any thread can listen for IO messages,
// although none are allowed to create new ones
// outside of threaded regions, all IO is permitted,
// but only on thread 1
int uvlock = 0;
if (_threadedregion) {
uvlock = jl_mutex_trylock(&jl_uv_mutex);
}
else if (ptls->tid == 0) {
uvlock = 1;
JL_UV_LOCK(); // jl_mutex_lock(&jl_uv_mutex);
}
if (uvlock) {
int active = 1;
if (jl_atomic_load(&jl_uv_n_waiters) != 0) {
// but if we won the race against someone who actually needs
// the lock to do real work, we need to let them have it instead
JL_UV_UNLOCK();
}
else {
// otherwise, we may block until someone asks us for the lock
uv_loop_t *loop = jl_global_event_loop();
jl_gc_safepoint();
if (may_sleep(ptls)) {
loop->stop_flag = 0;
JULIA_DEBUG_SLEEPWAKE( ptls->uv_run_enter = cycleclock() );
active = uv_run(loop, UV_RUN_ONCE);
JULIA_DEBUG_SLEEPWAKE( ptls->uv_run_leave = cycleclock() );
}
JL_UV_UNLOCK();
// optimization: check again first if we may have work to do
if (!may_sleep(ptls)) {
assert(ptls->sleep_check_state == not_sleeping);
start_cycles = 0;
continue;
}
// otherwise, we got a spurious wakeup since some other
// thread that just wanted to steal libuv from us,
// just go right back to sleep on the other wake signal
// to let them take it from us without conflict
// TODO: this relinquishes responsibility for all event
// to the last thread to do an explicit operation,
// which may starve other threads of critical work
if (jl_atomic_load(&jl_uv_n_waiters) == 0) {
continue;
}
}
if (!_threadedregion && active && ptls->tid == 0) {
// thread 0 is the only thread permitted to run the event loop
// so it needs to stay alive
if (jl_atomic_load_relaxed(&ptls->sleep_check_state) != not_sleeping)
jl_atomic_store(&ptls->sleep_check_state, not_sleeping); // let other threads know they don't need to wake us
start_cycles = 0;
continue;
}
}
// the other threads will just wait for on signal to resume
JULIA_DEBUG_SLEEPWAKE( ptls->sleep_enter = cycleclock() );
int8_t gc_state = jl_gc_safe_enter(ptls);
uv_mutex_lock(&ptls->sleep_lock);
while (may_sleep(ptls)) {
uv_cond_wait(&ptls->wake_signal, &ptls->sleep_lock);
// TODO: help with gc work here, if applicable
}
assert(ptls->sleep_check_state == not_sleeping);
uv_mutex_unlock(&ptls->sleep_lock);
JULIA_DEBUG_SLEEPWAKE( ptls->sleep_leave = cycleclock() );
jl_gc_safe_leave(ptls, gc_state); // contains jl_gc_safepoint
start_cycles = 0;
}
else {
// maybe check the kernel for new messages too
jl_process_events();
}
}
}
#ifdef __cplusplus
}
#endif
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