mirror of
https://github.com/autc04/Retro68.git
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200 lines
4.7 KiB
C
200 lines
4.7 KiB
C
// Copyright 2012 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Parallel for algorithm.
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#include "runtime.h"
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#include "arch.h"
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struct ParForThread
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{
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// the thread's iteration space [32lsb, 32msb)
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uint64 pos;
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// stats
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uint64 nsteal;
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uint64 nstealcnt;
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uint64 nprocyield;
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uint64 nosyield;
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uint64 nsleep;
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byte pad[CacheLineSize];
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};
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ParFor*
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runtime_parforalloc(uint32 nthrmax)
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{
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ParFor *desc;
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// The ParFor object is followed by CacheLineSize padding
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// and then nthrmax ParForThread.
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desc = (ParFor*)runtime_malloc(sizeof(ParFor) + CacheLineSize + nthrmax * sizeof(ParForThread));
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desc->thr = (ParForThread*)((byte*)(desc+1) + CacheLineSize);
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desc->nthrmax = nthrmax;
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return desc;
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}
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void
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runtime_parforsetup(ParFor *desc, uint32 nthr, uint32 n, void *ctx, bool wait, void (*body)(ParFor*, uint32))
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{
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uint32 i, begin, end;
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uint64 *pos;
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if(desc == nil || nthr == 0 || nthr > desc->nthrmax || body == nil) {
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runtime_printf("desc=%p nthr=%d count=%d body=%p\n", desc, nthr, n, body);
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runtime_throw("parfor: invalid args");
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}
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desc->body = body;
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desc->done = 0;
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desc->nthr = nthr;
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desc->thrseq = 0;
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desc->cnt = n;
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desc->ctx = ctx;
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desc->wait = wait;
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desc->nsteal = 0;
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desc->nstealcnt = 0;
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desc->nprocyield = 0;
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desc->nosyield = 0;
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desc->nsleep = 0;
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for(i=0; i<nthr; i++) {
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begin = (uint64)n*i / nthr;
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end = (uint64)n*(i+1) / nthr;
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pos = &desc->thr[i].pos;
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if(((uintptr)pos & 7) != 0)
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runtime_throw("parforsetup: pos is not aligned");
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*pos = (uint64)begin | (((uint64)end)<<32);
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}
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}
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void
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runtime_parfordo(ParFor *desc)
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{
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ParForThread *me;
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uint32 tid, begin, end, begin2, try, victim, i;
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uint64 *mypos, *victimpos, pos, newpos;
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void (*body)(ParFor*, uint32);
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bool idle;
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// Obtain 0-based thread index.
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tid = runtime_xadd(&desc->thrseq, 1) - 1;
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if(tid >= desc->nthr) {
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runtime_printf("tid=%d nthr=%d\n", tid, desc->nthr);
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runtime_throw("parfor: invalid tid");
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}
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// If single-threaded, just execute the for serially.
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if(desc->nthr==1) {
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for(i=0; i<desc->cnt; i++)
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desc->body(desc, i);
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return;
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}
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body = desc->body;
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me = &desc->thr[tid];
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mypos = &me->pos;
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for(;;) {
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for(;;) {
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// While there is local work,
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// bump low index and execute the iteration.
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pos = runtime_xadd64(mypos, 1);
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begin = (uint32)pos-1;
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end = (uint32)(pos>>32);
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if(begin < end) {
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body(desc, begin);
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continue;
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}
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break;
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}
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// Out of work, need to steal something.
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idle = false;
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for(try=0;; try++) {
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// If we don't see any work for long enough,
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// increment the done counter...
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if(try > desc->nthr*4 && !idle) {
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idle = true;
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runtime_xadd(&desc->done, 1);
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}
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// ...if all threads have incremented the counter,
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// we are done.
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if(desc->done + !idle == desc->nthr) {
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if(!idle)
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runtime_xadd(&desc->done, 1);
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goto exit;
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}
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// Choose a random victim for stealing.
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victim = runtime_fastrand1() % (desc->nthr-1);
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if(victim >= tid)
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victim++;
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victimpos = &desc->thr[victim].pos;
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for(;;) {
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// See if it has any work.
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pos = runtime_atomicload64(victimpos);
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begin = (uint32)pos;
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end = (uint32)(pos>>32);
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if(begin+1 >= end) {
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begin = end = 0;
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break;
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}
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if(idle) {
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runtime_xadd(&desc->done, -1);
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idle = false;
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}
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begin2 = begin + (end-begin)/2;
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newpos = (uint64)begin | (uint64)begin2<<32;
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if(runtime_cas64(victimpos, pos, newpos)) {
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begin = begin2;
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break;
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}
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}
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if(begin < end) {
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// Has successfully stolen some work.
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if(idle)
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runtime_throw("parfor: should not be idle");
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runtime_atomicstore64(mypos, (uint64)begin | (uint64)end<<32);
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me->nsteal++;
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me->nstealcnt += end-begin;
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break;
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}
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// Backoff.
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if(try < desc->nthr) {
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// nothing
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} else if (try < 4*desc->nthr) {
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me->nprocyield++;
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runtime_procyield(20);
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// If a caller asked not to wait for the others, exit now
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// (assume that most work is already done at this point).
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} else if (!desc->wait) {
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if(!idle)
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runtime_xadd(&desc->done, 1);
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goto exit;
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} else if (try < 6*desc->nthr) {
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me->nosyield++;
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runtime_osyield();
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} else {
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me->nsleep++;
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runtime_usleep(1);
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}
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}
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}
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exit:
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runtime_xadd64(&desc->nsteal, me->nsteal);
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runtime_xadd64(&desc->nstealcnt, me->nstealcnt);
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runtime_xadd64(&desc->nprocyield, me->nprocyield);
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runtime_xadd64(&desc->nosyield, me->nosyield);
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runtime_xadd64(&desc->nsleep, me->nsleep);
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me->nsteal = 0;
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me->nstealcnt = 0;
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me->nprocyield = 0;
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me->nosyield = 0;
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me->nsleep = 0;
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}
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// For testing from Go.
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void
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runtime_parforiters(ParFor *desc, uintptr tid, uintptr *start, uintptr *end)
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{
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*start = (uint32)desc->thr[tid].pos;
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*end = (uint32)(desc->thr[tid].pos>>32);
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}
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