runtime/src/kmp_taskdeps.cpp

/*
 * kmp_taskdeps.cpp
 */


//===----------------------------------------------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.txt for details.
//
//===----------------------------------------------------------------------===//


//#define KMP_SUPPORT_GRAPH_OUTPUT 1

#include "kmp.h"
#include "kmp_io.h"
#include "kmp_wait_release.h"

#if OMP_40_ENABLED

//TODO: Improve memory allocation? keep a list of pre-allocated structures? allocate in blocks? re-use list finished list entries?
//TODO: don't use atomic ref counters for stack-allocated nodes.
//TODO: find an alternate to atomic refs for heap-allocated nodes?
//TODO: Finish graph output support
//TODO: kmp_lock_t seems a tad to big (and heavy weight) for this. Check other runtime locks
//TODO: Any ITT support needed?

#ifdef KMP_SUPPORT_GRAPH_OUTPUT
static kmp_int32 kmp_node_id_seed = 0;
#endif

static void
__kmp_init_node ( kmp_depnode_t *node )
{
    node->dn.task = NULL; // set to null initially, it will point to the right task once dependences have been processed
    node->dn.successors = NULL;
    __kmp_init_lock(&node->dn.lock);
    node->dn.nrefs = 1; // init creates the first reference to the node
#ifdef KMP_SUPPORT_GRAPH_OUTPUT
    node->dn.id = KMP_TEST_THEN_INC32(&kmp_node_id_seed);
#endif
}

static inline kmp_depnode_t *
__kmp_node_ref ( kmp_depnode_t *node )
{
    KMP_TEST_THEN_INC32(&node->dn.nrefs);
    return node;
}

static inline void
__kmp_node_deref ( kmp_info_t *thread, kmp_depnode_t *node )
{
    if (!node) return;

    kmp_int32 n = KMP_TEST_THEN_DEC32(&node->dn.nrefs) - 1;
    if ( n == 0 ) {
        KMP_ASSERT(node->dn.nrefs == 0);
#if USE_FAST_MEMORY
        __kmp_fast_free(thread,node);
#else
        __kmp_thread_free(thread,node);
#endif
    }
}

#define KMP_ACQUIRE_DEPNODE(gtid,n) __kmp_acquire_lock(&(n)->dn.lock,(gtid))
#define KMP_RELEASE_DEPNODE(gtid,n) __kmp_release_lock(&(n)->dn.lock,(gtid))

static void
__kmp_depnode_list_free ( kmp_info_t *thread, kmp_depnode_list *list );

static const kmp_int32 kmp_dephash_log2 = 6;
static const kmp_int32 kmp_dephash_size = (1 << kmp_dephash_log2);

static inline kmp_int32
__kmp_dephash_hash ( kmp_intptr_t addr )
{
    //TODO alternate to try: set = (((Addr64)(addrUsefulBits * 9.618)) % m_num_sets );
    return ((addr >> kmp_dephash_log2) ^ addr) % kmp_dephash_size;
}

static kmp_dephash_t *
__kmp_dephash_create ( kmp_info_t *thread )
{
    kmp_dephash_t *h;

    kmp_int32 size = kmp_dephash_size * sizeof(kmp_dephash_entry_t) + sizeof(kmp_dephash_t);

#if USE_FAST_MEMORY
    h = (kmp_dephash_t *) __kmp_fast_allocate( thread, size );
#else
    h = (kmp_dephash_t *) __kmp_thread_malloc( thread, size );
#endif

#ifdef KMP_DEBUG
    h->nelements = 0;
#endif
    h->buckets = (kmp_dephash_entry **)(h+1);

    for ( kmp_int32 i = 0; i < kmp_dephash_size; i++ )
        h->buckets[i] = 0;

    return h;
}

static void
__kmp_dephash_free ( kmp_info_t *thread, kmp_dephash_t *h )
{
    for ( kmp_int32 i=0; i < kmp_dephash_size; i++ ) {
        if ( h->buckets[i] ) {
            kmp_dephash_entry_t *next;
            for ( kmp_dephash_entry_t *entry = h->buckets[i]; entry; entry = next ) {
                next = entry->next_in_bucket;
                __kmp_depnode_list_free(thread,entry->last_ins);
                __kmp_node_deref(thread,entry->last_out);
#if USE_FAST_MEMORY
                __kmp_fast_free(thread,entry);
#else
                __kmp_thread_free(thread,entry);
#endif
            }
        }
    }
#if USE_FAST_MEMORY
    __kmp_fast_free(thread,h);
#else
    __kmp_thread_free(thread,h);
#endif
}

static kmp_dephash_entry *
__kmp_dephash_find ( kmp_info_t *thread, kmp_dephash_t *h, kmp_intptr_t addr )
{
    kmp_int32 bucket = __kmp_dephash_hash(addr);

    kmp_dephash_entry_t *entry;
    for ( entry = h->buckets[bucket]; entry; entry = entry->next_in_bucket )
        if ( entry->addr == addr ) break;

    if ( entry == NULL ) {
        // create entry. This is only done by one thread so no locking required
#if USE_FAST_MEMORY
        entry = (kmp_dephash_entry_t *) __kmp_fast_allocate( thread, sizeof(kmp_dephash_entry_t) );
#else
        entry = (kmp_dephash_entry_t *) __kmp_thread_malloc( thread, sizeof(kmp_dephash_entry_t) );
#endif
        entry->addr = addr;
        entry->last_out = NULL;
        entry->last_ins = NULL;
        entry->next_in_bucket = h->buckets[bucket];
        h->buckets[bucket] = entry;
#ifdef KMP_DEBUG
        h->nelements++;
        if ( entry->next_in_bucket ) h->nconflicts++;
#endif
    }
    return entry;
}

static kmp_depnode_list_t *
__kmp_add_node ( kmp_info_t *thread, kmp_depnode_list_t *list, kmp_depnode_t *node )
{
    kmp_depnode_list_t *new_head;

#if USE_FAST_MEMORY
    new_head = (kmp_depnode_list_t *) __kmp_fast_allocate(thread,sizeof(kmp_depnode_list_t));
#else
    new_head = (kmp_depnode_list_t *) __kmp_thread_malloc(thread,sizeof(kmp_depnode_list_t));
#endif

    new_head->node = __kmp_node_ref(node);
    new_head->next = list;

    return new_head;
}

static void
__kmp_depnode_list_free ( kmp_info_t *thread, kmp_depnode_list *list )
{
    kmp_depnode_list *next;

    for ( ; list ; list = next ) {
        next = list->next;

        __kmp_node_deref(thread,list->node);
#if USE_FAST_MEMORY
        __kmp_fast_free(thread,list);
#else
        __kmp_thread_free(thread,list);
#endif
    }
}

static inline void
__kmp_track_dependence ( kmp_depnode_t *source, kmp_depnode_t *sink )
{
#ifdef KMP_SUPPORT_GRAPH_OUTPUT
    kmp_taskdata_t * task_source = KMP_TASK_TO_TASKDATA(source->dn.task);
    kmp_taskdata_t * task_sink = KMP_TASK_TO_TASKDATA(sink->dn.task);    // this can be NULL when if(0) ...

    __kmp_printf("%d(%s) -> %d(%s)\n", source->dn.id, task_source->td_ident->psource, sink->dn.id, task_sink->td_ident->psource);
#endif
}

template< bool filter >
static inline kmp_int32
__kmp_process_deps ( kmp_int32 gtid, kmp_depnode_t *node, kmp_dephash_t *hash,
                     bool dep_barrier,kmp_int32 ndeps, kmp_depend_info_t *dep_list)
{
    KA_TRACE(30, ("__kmp_process_deps<%d>: T#%d processing %d depencies : dep_barrier = %d\n", filter, gtid, ndeps, dep_barrier ) );

    kmp_info_t *thread = __kmp_threads[ gtid ];
    kmp_int32 npredecessors=0;
    for ( kmp_int32 i = 0; i < ndeps ; i++ ) {
        const kmp_depend_info_t * dep = &dep_list[i];

        KMP_DEBUG_ASSERT(dep->flags.in);

        if ( filter && dep->base_addr == 0 ) continue; // skip filtered entries

        kmp_dephash_entry_t *info = __kmp_dephash_find(thread,hash,dep->base_addr);
        kmp_depnode_t *last_out = info->last_out;

        if ( dep->flags.out && info->last_ins ) {
            for ( kmp_depnode_list_t * p = info->last_ins; p; p = p->next ) {
                kmp_depnode_t * indep = p->node;
                if ( indep->dn.task ) {
                    KMP_ACQUIRE_DEPNODE(gtid,indep);
                    if ( indep->dn.task ) {
                        __kmp_track_dependence(indep,node);
                        indep->dn.successors = __kmp_add_node(thread, indep->dn.successors, node);
                        KA_TRACE(40,("__kmp_process_deps<%d>: T#%d adding dependence from %p to %p",
                                 filter,gtid, KMP_TASK_TO_TASKDATA(indep->dn.task), KMP_TASK_TO_TASKDATA(node->dn.task)));
                        npredecessors++;
                    }
                    KMP_RELEASE_DEPNODE(gtid,indep);
                }
            }

            __kmp_depnode_list_free(thread,info->last_ins);
            info->last_ins = NULL;

        } else if ( last_out && last_out->dn.task ) {
            KMP_ACQUIRE_DEPNODE(gtid,last_out);
            if ( last_out->dn.task ) {
                __kmp_track_dependence(last_out,node);
                last_out->dn.successors = __kmp_add_node(thread, last_out->dn.successors, node);
                KA_TRACE(40,("__kmp_process_deps<%d>: T#%d adding dependence from %p to %p",
                             filter,gtid, KMP_TASK_TO_TASKDATA(last_out->dn.task), KMP_TASK_TO_TASKDATA(node->dn.task)));

                npredecessors++;
            }
            KMP_RELEASE_DEPNODE(gtid,last_out);
        }

        if ( dep_barrier ) {
            // if this is a sync point in the serial sequence, then the previous outputs are guaranteed to be completed after
            // the execution of this task so the previous output nodes can be cleared.
            __kmp_node_deref(thread,last_out);
            info->last_out = NULL;
        } else {
            if ( dep->flags.out ) {
                __kmp_node_deref(thread,last_out);
                info->last_out = __kmp_node_ref(node);
            } else
                info->last_ins = __kmp_add_node(thread, info->last_ins, node);
        }

    }

    KA_TRACE(30, ("__kmp_process_deps<%d>: T#%d found %d predecessors\n", filter, gtid, npredecessors ) );

    return npredecessors;
}

#define NO_DEP_BARRIER (false)
#define DEP_BARRIER (true)

// returns true if the task has any outstanding dependence
static bool
__kmp_check_deps ( kmp_int32 gtid, kmp_depnode_t *node, kmp_task_t *task, kmp_dephash_t *hash, bool dep_barrier,
                   kmp_int32 ndeps, kmp_depend_info_t *dep_list,
                   kmp_int32 ndeps_noalias, kmp_depend_info_t *noalias_dep_list )
{
    int i;

    kmp_taskdata_t * taskdata = KMP_TASK_TO_TASKDATA(task);
    KA_TRACE(20, ("__kmp_check_deps: T#%d checking dependencies for task %p : %d possibly aliased dependencies, %d non-aliased depedencies : dep_barrier=%d .\n", gtid, taskdata, ndeps, ndeps_noalias, dep_barrier ) );

    // Filter deps in dep_list
    // TODO: Different algorithm for large dep_list ( > 10 ? )
    for ( i = 0; i < ndeps; i ++ ) {
        if ( dep_list[i].base_addr != 0 )
            for ( int j = i+1; j < ndeps; j++ )
                if ( dep_list[i].base_addr == dep_list[j].base_addr ) {
                    dep_list[i].flags.in |= dep_list[j].flags.in;
                    dep_list[i].flags.out |= dep_list[j].flags.out;
                    dep_list[j].base_addr = 0; // Mark j element as void
                }
    }

    // doesn't need to be atomic as no other thread is going to be accessing this node just yet
    // npredecessors is set -1 to ensure that none of the releasing tasks queues this task before we have finished processing all the dependencies
    node->dn.npredecessors = -1;

    // used to pack all npredecessors additions into a single atomic operation at the end
    int npredecessors;

    npredecessors = __kmp_process_deps<true>(gtid, node, hash, dep_barrier, ndeps, dep_list);
    npredecessors += __kmp_process_deps<false>(gtid, node, hash, dep_barrier, ndeps_noalias, noalias_dep_list);

    node->dn.task = task;
    KMP_MB();

    // Account for our initial fake value
    npredecessors++;

    // Update predecessors and obtain current value to check if there are still any outstandig dependences (some tasks may have finished while we processed the dependences)
    npredecessors = KMP_TEST_THEN_ADD32(&node->dn.npredecessors, npredecessors) + npredecessors;

    KA_TRACE(20, ("__kmp_check_deps: T#%d found %d predecessors for task %p \n", gtid, npredecessors, taskdata ) );

    // beyond this point the task could be queued (and executed) by a releasing task...
    return npredecessors > 0 ? true : false;
}

void
__kmp_release_deps ( kmp_int32 gtid, kmp_taskdata_t *task )
{
    kmp_info_t *thread = __kmp_threads[ gtid ];
    kmp_depnode_t *node = task->td_depnode;

    if ( task->td_dephash ) {
        KA_TRACE(40, ("__kmp_realease_deps: T#%d freeing dependencies hash of task %p.\n", gtid, task ) );
        __kmp_dephash_free(thread,task->td_dephash);
    }

    if ( !node ) return;

    KA_TRACE(20, ("__kmp_realease_deps: T#%d notifying succesors of task %p.\n", gtid, task ) );

    KMP_ACQUIRE_DEPNODE(gtid,node);
    node->dn.task = NULL; // mark this task as finished, so no new dependencies are generated
    KMP_RELEASE_DEPNODE(gtid,node);

    kmp_depnode_list_t *next;
    for ( kmp_depnode_list_t *p = node->dn.successors; p; p = next ) {
        kmp_depnode_t *successor = p->node;
        kmp_int32 npredecessors = KMP_TEST_THEN_DEC32(&successor->dn.npredecessors) - 1;

        // successor task can be NULL for wait_depends or because deps are still being processed
        if ( npredecessors == 0 ) {
            KMP_MB();
            if ( successor->dn.task ) {
                KA_TRACE(20, ("__kmp_realease_deps: T#%d successor %p of %p scheduled for execution.\n", gtid, successor->dn.task, task ) );
                __kmp_omp_task(gtid,successor->dn.task,false);
            }
        }

        next = p->next;
        __kmp_node_deref(thread,p->node);
#if USE_FAST_MEMORY
        __kmp_fast_free(thread,p);
#else
        __kmp_thread_free(thread,p);
#endif
    }

    __kmp_node_deref(thread,node);

    KA_TRACE(20, ("__kmp_realease_deps: T#%d all successors of %p notified of completation\n", gtid, task ) );
}

/*!
@ingroup TASKING
@param loc_ref location of the original task directive
@param gtid Global Thread ID of encountering thread
@param new_task task thunk allocated by __kmp_omp_task_alloc() for the ''new task''
@param ndeps Number of depend items with possible aliasing
@param dep_list List of depend items with possible aliasing
@param ndeps_noalias Number of depend items with no aliasing
@param noalias_dep_list List of depend items with no aliasing

@return Returns either TASK_CURRENT_NOT_QUEUED if the current task was not suspendend and queued, or TASK_CURRENT_QUEUED if it was suspended and queued

Schedule a non-thread-switchable task with dependences for execution
*/
kmp_int32
__kmpc_omp_task_with_deps( ident_t *loc_ref, kmp_int32 gtid, kmp_task_t * new_task,
                            kmp_int32 ndeps, kmp_depend_info_t *dep_list,
                            kmp_int32 ndeps_noalias, kmp_depend_info_t *noalias_dep_list )
{

    kmp_taskdata_t * new_taskdata = KMP_TASK_TO_TASKDATA(new_task);
    KA_TRACE(10, ("__kmpc_omp_task_with_deps(enter): T#%d loc=%p task=%p\n",
                  gtid, loc_ref, new_taskdata ) );

    kmp_info_t *thread = __kmp_threads[ gtid ];
    kmp_taskdata_t * current_task = thread->th.th_current_task;

    bool serial = current_task->td_flags.team_serial || current_task->td_flags.tasking_ser || current_task->td_flags.final;

    if ( !serial && ( ndeps > 0 || ndeps_noalias > 0 )) {
        /* if no dependencies have been tracked yet, create the dependence hash */
        if ( current_task->td_dephash == NULL )
            current_task->td_dephash = __kmp_dephash_create(thread);

#if USE_FAST_MEMORY
        kmp_depnode_t *node = (kmp_depnode_t *) __kmp_fast_allocate(thread,sizeof(kmp_depnode_t));
#else
        kmp_depnode_t *node = (kmp_depnode_t *) __kmp_thread_malloc(thread,sizeof(kmp_depnode_t));
#endif

        __kmp_init_node(node);
        new_taskdata->td_depnode = node;

        if ( __kmp_check_deps( gtid, node, new_task, current_task->td_dephash, NO_DEP_BARRIER,
                               ndeps, dep_list, ndeps_noalias,noalias_dep_list ) ) {
            KA_TRACE(10, ("__kmpc_omp_task_with_deps(exit): T#%d task had blocking dependencies: "
                  "loc=%p task=%p, return: TASK_CURRENT_NOT_QUEUED\n", gtid, loc_ref,
                  new_taskdata ) );
            return TASK_CURRENT_NOT_QUEUED;
        }
    }

    KA_TRACE(10, ("__kmpc_omp_task_with_deps(exit): T#%d task had no blocking dependencies : "
                  "loc=%p task=%p, transferring to __kmpc_omp_task\n", gtid, loc_ref,
                  new_taskdata ) );

    return __kmpc_omp_task(loc_ref,gtid,new_task);
}

/*!
@ingroup TASKING
@param loc_ref location of the original task directive
@param gtid Global Thread ID of encountering thread
@param ndeps Number of depend items with possible aliasing
@param dep_list List of depend items with possible aliasing
@param ndeps_noalias Number of depend items with no aliasing
@param noalias_dep_list List of depend items with no aliasing

Blocks the current task until all specifies dependencies have been fulfilled.
*/
void
__kmpc_omp_wait_deps ( ident_t *loc_ref, kmp_int32 gtid, kmp_int32 ndeps, kmp_depend_info_t *dep_list,
                       kmp_int32 ndeps_noalias, kmp_depend_info_t *noalias_dep_list )
{
    KA_TRACE(10, ("__kmpc_omp_wait_deps(enter): T#%d loc=%p\n", gtid, loc_ref) );

    if ( ndeps == 0 && ndeps_noalias == 0 ) {
        KA_TRACE(10, ("__kmpc_omp_wait_deps(exit): T#%d has no dependencies to wait upon : loc=%p\n", gtid, loc_ref) );
        return;
    }

    kmp_info_t *thread = __kmp_threads[ gtid ];
    kmp_taskdata_t * current_task = thread->th.th_current_task;

    // We can return immediately as:
    //   - dependences are not computed in serial teams
    //   - if the dephash is not yet created it means we have nothing to wait for
    if ( current_task->td_flags.team_serial || current_task->td_flags.tasking_ser || current_task->td_flags.final || current_task->td_dephash == NULL ) {
        KA_TRACE(10, ("__kmpc_omp_wait_deps(exit): T#%d has no blocking dependencies : loc=%p\n", gtid, loc_ref) );
        return;
    }

    kmp_depnode_t node;
    __kmp_init_node(&node);

    if (!__kmp_check_deps( gtid, &node, NULL, current_task->td_dephash, DEP_BARRIER,
                           ndeps, dep_list, ndeps_noalias, noalias_dep_list )) {
        KA_TRACE(10, ("__kmpc_omp_wait_deps(exit): T#%d has no blocking dependencies : loc=%p\n", gtid, loc_ref) );
        return;
    }

    int thread_finished = FALSE;
    kmp_flag_32 flag((volatile kmp_uint32 *)&(node.dn.npredecessors), 0U);
    while ( node.dn.npredecessors > 0 ) {
        flag.execute_tasks(thread, gtid, FALSE, &thread_finished,
#if USE_ITT_BUILD
                           NULL,
#endif
                           __kmp_task_stealing_constraint );
    }

    KA_TRACE(10, ("__kmpc_omp_wait_deps(exit): T#%d finished waiting : loc=%p\n", gtid, loc_ref) );
}

#endif /* OMP_40_ENABLED */