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[Offload] Make the RPC thread sleep briefly when idle #168596

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[Offload] Make the RPC thread sleep briefly when idle #168596

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21 changes: 18 additions & 3 deletions offload/plugins-nextgen/common/src/RPC.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -83,7 +83,8 @@ static rpc::Status handleOffloadOpcodes(plugin::GenericDeviceTy &Device,
return rpc::RPC_ERROR;
}

static rpc::Status runServer(plugin::GenericDeviceTy &Device, void *Buffer) {
static rpc::Status runServer(plugin::GenericDeviceTy &Device, void *Buffer,
bool &ClientInUse) {
uint64_t NumPorts =
std::min(Device.requestedRPCPortCount(), rpc::MAX_PORT_COUNT);
rpc::Server Server(NumPorts, Buffer);
Expand All @@ -92,14 +93,14 @@ static rpc::Status runServer(plugin::GenericDeviceTy &Device, void *Buffer) {
if (!Port)
return rpc::RPC_SUCCESS;

ClientInUse = true;
rpc::Status Status =
handleOffloadOpcodes(Device, *Port, Device.getWarpSize());

// Let the `libc` library handle any other unhandled opcodes.
if (Status == rpc::RPC_UNHANDLED_OPCODE)
Status = LIBC_NAMESPACE::shared::handle_libc_opcodes(*Port,
Device.getWarpSize());

Port->close();

return Status;
Expand All @@ -122,7 +123,11 @@ void RPCServerTy::ServerThread::shutDown() {
}

void RPCServerTy::ServerThread::run() {
static constexpr auto IdleTime = std::chrono::microseconds(25);
static constexpr auto IdleSleep = std::chrono::microseconds(250);
std::unique_lock<decltype(Mutex)> Lock(Mutex);

auto LastUse = std::chrono::steady_clock::now();
for (;;) {
CV.wait(Lock, [&]() {
return NumUsers.load(std::memory_order_acquire) > 0 ||
Expand All @@ -133,15 +138,25 @@ void RPCServerTy::ServerThread::run() {
return;

Lock.unlock();
bool ClientInUse = false;
while (NumUsers.load(std::memory_order_relaxed) > 0 &&
Running.load(std::memory_order_relaxed)) {

// Suspend this thread briefly if there is no current work.
auto Now = std::chrono::steady_clock::now();
if (!ClientInUse && Now - LastUse >= IdleTime)
std::this_thread::sleep_for(IdleSleep);
else if (ClientInUse)
LastUse = Now;

ClientInUse = false;
std::lock_guard<decltype(Mutex)> Lock(BufferMutex);
for (const auto &[Buffer, Device] : llvm::zip_equal(Buffers, Devices)) {
if (!Buffer || !Device)
continue;

// If running the server failed, print a message but keep running.
if (runServer(*Device, Buffer) != rpc::RPC_SUCCESS)
if (runServer(*Device, Buffer, ClientInUse) != rpc::RPC_SUCCESS)
FAILURE_MESSAGE("Unhandled or invalid RPC opcode!");
}
}
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