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replace of the "fence" changes from PR #550 #552

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replace of the "fence" changes from PR #550 #552

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149 changes: 96 additions & 53 deletions src/madness/world/worldgop.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -47,109 +47,152 @@ namespace madness {
/// constant over two traversals. We are then we are sure
/// that all tasks and AM are processed and there no AM in
/// flight.
/// \post `this->world_.taskq.size()==0`
void WorldGopInterface::fence_impl(std::function<void()> epilogue,
bool pause_during_epilogue,
bool debug) {
PROFILE_MEMBER_FUNC(WorldGopInterface);
MADNESS_CHECK(not forbid_fence_);
unsigned long nsent_prev=0, nrecv_prev=1; // invalid initial condition
unsigned long nsent_prev=0, nrecv_prev=1;
SafeMPI::Request req0, req1;
ProcessID parent, child0, child1;
world_.mpi.binary_tree_info(0, parent, child0, child1);
Tag gfence_tag = world_.mpi.unique_tag();
Tag bcast_tag = world_.mpi.unique_tag();
int npass = 0;

//double start = wall_time();

if (debug)
madness::print(world_.rank(), ": WORLD.GOP.FENCE: entering fence loop, gfence_tag=", gfence_tag, " bcast_tag=", bcast_tag);

while (1) {
uint64_t sum0[2]={0,0}, sum1[2]={0,0}, sum[2];
if (child0 != -1) req0 = world_.mpi.Irecv((void*) &sum0, sizeof(sum0), MPI_BYTE, child0, gfence_tag);
if (child1 != -1) req1 = world_.mpi.Irecv((void*) &sum1, sizeof(sum1), MPI_BYTE, child1, gfence_tag);
// fence ensures that all ranks agree that all sent AMs (nsent) have been
// processed (nrecv) and that no tasks (ntask) are running. We ensure this by
// observing the global sums of these local observables, and then ensuring
// that the termination conditions have been met twice and
// over two rounds of observations no messages have been met.
// N.B. Epilogue and deferred cleanup can also generate messages, so
// need to do another round of global synchronization after these
// actions ... hence the lambda

auto termdet = [&]() {
if (debug)
madness::print(
world_.rank(),
": WORLD.GOP.FENCE: entering termdet, gfence_tag=",
gfence_tag, " bcast_tag=", bcast_tag);

while (1) {
uint64_t sum0[2] = {0, 0}, sum1[2] = {0, 0}, sum[2];
if (child0 != -1)
req0 = world_.mpi.Irecv((void *)&sum0, sizeof(sum0), MPI_BYTE,
child0, gfence_tag);
if (child1 != -1)
req1 = world_.mpi.Irecv((void *)&sum1, sizeof(sum1), MPI_BYTE,
child1, gfence_tag);
world_.taskq.fence();
if (child0 != -1) World::await(req0);
if (child1 != -1) World::await(req1);
if (child0 != -1)
World::await(req0);
if (child1 != -1)
World::await(req1);

if (debug && (child0 != -1 || child1 != -1))
madness::print(world_.rank(), ": WORLD.GOP.FENCE: npass=", npass, " received messages from children={", child0, ",", child1, "} gfence_tag=", gfence_tag);
madness::print(world_.rank(),
": WORLD.GOP.FENCE: npass=", npass,
" received messages from children={", child0,
",", child1, "} gfence_tag=", gfence_tag);

bool finished;
uint64_t ntask1, nsent1, nrecv1, ntask2, nsent2, nrecv2;
do {
world_.taskq.fence();
world_.taskq.fence();

// Since the number of outstanding tasks and number of AM sent/recv
// don't share a critical section read each twice and ensure they
// are unchanged to ensure that are consistent ... they don't have
// to be current.
// Since the number of outstanding tasks and number of AM sent/recv
// don't share a critical section there is no good way to obtain
// their "current" values (i.e. their values at the same clock),
// so read each twice and ensure they are unchanged to ensure
// that are consistent ...

ntask1 = world_.taskq.size();
nsent1 = world_.am.nsent;
nrecv1 = world_.am.nrecv;
nsent1 = world_.am.nsent; // # of sent AM
nrecv1 = world_.am.nrecv; // # of processed incoming AM
ntask1 = world_.taskq.size(); // current # of tasks; N.B. this was zero after the fence above but may be non-zero now
// processing each incoming AMs may bump this up, so read it AFTER nrecv (albeit task completion will drop this again)

__asm__ __volatile__ (" " : : : "memory");
__asm__ __volatile__(" " : : : "memory");

ntask2 = world_.taskq.size();
nsent2 = world_.am.nsent;
nrecv2 = world_.am.nrecv;
nsent2 = world_.am.nsent;
nrecv2 = world_.am.nrecv;
ntask2 = world_.taskq.size();

__asm__ __volatile__ (" " : : : "memory");
__asm__ __volatile__(" " : : : "memory");

finished = (ntask2==0) && (ntask1==0) && (nsent1==nsent2) && (nrecv1==nrecv2);
}
while (!finished);
finished = (ntask2 == 0) && (ntask1 == 0) &&
(nsent1 == nsent2) && (nrecv1 == nrecv2);
} while (!finished);

sum[0] = sum0[0] + sum1[0] + nsent2; // Must use values read above
sum[0] =
sum0[0] + sum1[0] + nsent2;
sum[1] = sum0[1] + sum1[1] + nrecv2;

if (parent != -1) {
req0 = world_.mpi.Isend(&sum, sizeof(sum), MPI_BYTE, parent, gfence_tag);
if (debug)
madness::print(world_.rank(), ": WORLD.GOP.FENCE: npass=", npass, " sent message to parent=", parent, " gfence_tag=", gfence_tag);
World::await(req0);
if (debug)
madness::print(world_.rank(), ": WORLD.GOP.FENCE: npass=", npass, " parent=", parent, ", confirmed receipt");
req0 = world_.mpi.Isend(&sum, sizeof(sum), MPI_BYTE, parent,
gfence_tag);
if (debug)
madness::print(world_.rank(),
": WORLD.GOP.FENCE: npass=", npass,
" sent message to parent=", parent,
" gfence_tag=", gfence_tag);
World::await(req0);
if (debug)
madness::print(world_.rank(),
": WORLD.GOP.FENCE: npass=", npass,
" parent=", parent, ", confirmed receipt");
}

// While we are probably idle free unused communication buffers
//world_.am.free_managed_buffers();

//bool dowork = (npass==0) || (ThreadPool::size()==0);
// bool dowork = (npass==0) || (ThreadPool::size()==0);
bool dowork = true;
broadcast(&sum, sizeof(sum), 0, dowork, bcast_tag);
++npass;

if (debug)
madness::print(world_.rank(), ": WORLD.GOP.FENCE: npass=", npass, " sum0=", sum[0], " nsent_prev=", nsent_prev, " sum1=", sum[1], " nrecv_prev=", nrecv_prev);
madness::print(world_.rank(),
": WORLD.GOP.FENCE: npass=", npass,
" sum0=", sum[0], " nsent_prev=", nsent_prev,
" sum1=", sum[1], " nrecv_prev=", nrecv_prev);

if (sum[0]==sum[1] && sum[0]==nsent_prev && sum[1]==nrecv_prev) {
if (sum[0] == sum[1] && sum[0] == nsent_prev &&
sum[1] == nrecv_prev) {
if (debug)
madness::print(world_.rank(), ": WORLD.GOP.FENCE: npass=", npass, " exiting fence loop");
madness::print(world_.rank(),
": WORLD.GOP.FENCE: npass=", npass,
" exiting fence loop");
break;
}

// if (wall_time() - start > 1200.0) {
// std::cout << rank() << " FENCE " << nsent2 << " "
// << nsent_prev << " " << nrecv2 << " " << nrecv_prev
// << " " << sum[0] << " " << sum[1] << " " << npass
// << " " << taskq.size() << std::endl;
// std::cout.flush();
// //myusleep(1000);
// MADNESS_ASSERT(0);
// }
// if (wall_time() - start > 1200.0) {
// std::cout << rank() << " FENCE " << nsent2 << " "
// << nsent_prev << " " << nrecv2 << " " << nrecv_prev
// << " " << sum[0] << " " << sum[1] << " " << npass
// << " " << taskq.size() << std::endl;
// std::cout.flush();
// //myusleep(1000);
// MADNESS_ASSERT(0);
// }

nsent_prev = sum[0];
nrecv_prev = sum[1];
};
}; // termdet

termdet();

};
// execute post-fence actions
MADNESS_ASSERT(pause_during_epilogue == false);
epilogue();
world_.am.free_managed_buffers(); // free up communication buffers
deferred_->do_cleanup();

// repeat termination detection in case epilogue or cleanup produced tasks
termdet();

// ensure postcondition
world_.taskq.fence();

#ifdef MADNESS_HAS_GOOGLE_PERF_TCMALLOC
MallocExtension::instance()->ReleaseFreeMemory();
// print("clearing memory");
Expand Down
10 changes: 5 additions & 5 deletions src/madness/world/worldgop.h
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Original file line number Diff line number Diff line change
Expand Up @@ -706,14 +706,14 @@ namespace madness {

/// Synchronizes all processes in communicator AND globally ensures no pending AM or tasks

/// \internal Runs Dykstra-like termination algorithm on binary tree by
/// locally ensuring ntask=0 and all am sent and processed,
/// and then participating in a global sum of nsent and nrecv.
/// Then globally checks that nsent=nrecv and that both are
/// constant over two traversals. We are then sure
/// \internal Runs Dykstra-like termination algorithm on binary tree
/// which stops when global sum of # of tasks in queue (`ntask`) is
/// zero and global sum of the # of sent/received AMs (`nsent`/`nrecv`)
/// are equal and unchanged over two traversals. We are then sure
/// that all tasks and AM are processed and there no AM in
/// flight.
/// \param[in] debug set to true to print progress statistics using madness::print(); the default is false.
/// \post `this->gop.taskq.size()==0`
void fence(bool debug = false);

/// Executes an action on single (this) thread after ensuring all other work is done
Expand Down
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