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/*
* Copyright (c) 2014-2015 Advanced Micro Devices, Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* 3. Neither the name of the copyright holder nor the names of its
* contributors may be used to endorse or promote products derived from this
* software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#include "gpu-compute/scoreboard_check_stage.hh"
#include "debug/GPUExec.hh"
#include "debug/GPUSched.hh"
#include "debug/GPUSync.hh"
#include "gpu-compute/compute_unit.hh"
#include "gpu-compute/gpu_static_inst.hh"
#include "gpu-compute/scalar_register_file.hh"
#include "gpu-compute/shader.hh"
#include "gpu-compute/vector_register_file.hh"
#include "gpu-compute/wavefront.hh"
#include "params/ComputeUnit.hh"
namespace gem5
{
ScoreboardCheckStage::ScoreboardCheckStage(const ComputeUnitParams &p,
ComputeUnit &cu,
ScoreboardCheckToSchedule
&to_schedule)
: computeUnit(cu), toSchedule(to_schedule),
_name(cu.name() + ".ScoreboardCheckStage"), stats(&cu)
{
}
ScoreboardCheckStage::~ScoreboardCheckStage()
{
}
void
ScoreboardCheckStage::collectStatistics(nonrdytype_e rdyStatus)
{
panic_if(rdyStatus == NRDY_ILLEGAL || rdyStatus >= NRDY_CONDITIONS,
"Instruction ready status %d is illegal!!!", rdyStatus);
stats.stallCycles[rdyStatus]++;
}
// Return true if this wavefront is ready
// to execute an instruction of the specified type.
// It also returns the reason (in rdyStatus) if the instruction is not
// ready. Finally it sets the execution resource type (in exesResType)
// of the instruction, only if it ready.
bool
ScoreboardCheckStage::ready(Wavefront *w, nonrdytype_e *rdyStatus,
int *exeResType, int wfSlot)
{
/**
* The waitCnt checks have to be done BEFORE checking for Instruction
* buffer empty condition. Otherwise, it will result into a deadlock if
* the last instruction in the Instruction buffer is a waitCnt: after
* executing the waitCnt, the Instruction buffer would be empty and the
* ready check logic will exit BEFORE checking for wait counters being
* satisfied.
*/
// waitCnt instruction has been dispatched or executed: next
// instruction should be blocked until waitCnts are satisfied.
if (w->getStatus() == Wavefront::S_WAITCNT) {
if (!w->waitCntsSatisfied()) {
*rdyStatus = NRDY_WAIT_CNT;
return false;
}
}
// sleep instruction has been dispatched or executed: next
// instruction should be blocked until the sleep period expires.
if (w->getStatus() == Wavefront::S_STALLED_SLEEP) {
if (!w->sleepDone()) {
*rdyStatus = NRDY_SLEEP;
return false;
}
}
// Is the wave waiting at a barrier. Check this condition BEFORE checking
// for instruction buffer occupancy to avoid a deadlock when the barrier is
// the last instruction in the instruction buffer.
if (w->getStatus() == Wavefront::S_BARRIER) {
assert(w->hasBarrier());
int bar_id = w->barrierId();
if (!computeUnit.allAtBarrier(bar_id)) {
DPRINTF(GPUSync, "CU[%d] WF[%d][%d] Wave[%d] - Stalled at "
"barrier Id%d. %d waves remain.\n", w->computeUnit->cu_id,
w->simdId, w->wfSlotId, w->wfDynId, bar_id,
w->computeUnit->numYetToReachBarrier(bar_id));
// Are all threads at barrier?
*rdyStatus = NRDY_BARRIER_WAIT;
return false;
}
DPRINTF(GPUSync, "CU[%d] WF[%d][%d] Wave[%d] - All waves at barrier "
"Id%d. Resetting barrier resources.\n", w->computeUnit->cu_id,
w->simdId, w->wfSlotId, w->wfDynId, bar_id);
computeUnit.resetBarrier(bar_id);
computeUnit.releaseWFsFromBarrier(bar_id);
}
// Check WF status: it has to be running
if (w->getStatus() == Wavefront::S_STOPPED ||
w->getStatus() == Wavefront::S_RETURNING ||
w->getStatus() == Wavefront::S_STALLED) {
*rdyStatus = NRDY_WF_STOP;
return false;
}
// is the Instruction buffer empty
if ( w->instructionBuffer.empty()) {
*rdyStatus = NRDY_IB_EMPTY;
return false;
}
// Check next instruction from instruction buffer
GPUDynInstPtr ii = w->nextInstr();
// Only instruction in the instruction buffer has been dispatched.
// No need to check it again for readiness
if (!ii) {
*rdyStatus = NRDY_IB_EMPTY;
return false;
}
// The following code is very error prone and the entire process for
// checking readiness will be fixed eventually. In the meantime, let's
// make sure that we do not silently let an instruction type slip
// through this logic and always return not ready.
if (!(ii->isBarrier() || ii->isNop() || ii->isReturn() || ii->isBranch() ||
ii->isALU() || ii->isLoad() || ii->isStore() || ii->isAtomic() ||
ii->isEndOfKernel() || ii->isMemSync() || ii->isFlat() ||
ii->isFlatGlobal() || ii->isSleep() || ii->isLocalMem())) {
panic("next instruction: %s is of unknown type\n", ii->disassemble());
}
DPRINTF(GPUExec, "CU%d: WF[%d][%d]: Checking Ready for Inst : %s\n",
computeUnit.cu_id, w->simdId, w->wfSlotId, ii->disassemble());
// Non-scalar (i.e., vector) instructions may use VGPRs
if (!ii->isScalar()) {
if (!computeUnit.vrf[w->simdId]->operandsReady(w, ii)) {
*rdyStatus = NRDY_VGPR_NRDY;
return false;
}
}
// Scalar and non-scalar instructions may use SGPR
if (!computeUnit.srf[w->simdId]->operandsReady(w, ii)) {
*rdyStatus = NRDY_SGPR_NRDY;
return false;
}
// The hardware implicitly executes S_WAITCNT 0 before executing
// the S_ENDPGM instruction. Implementing this implicit S_WAITCNT.
// isEndOfKernel() is used to identify the S_ENDPGM instruction
// On identifying it, we do the following:
// 1. Wait for all older instruction to execute
// 2. Once all the older instruction are executed, we add a wait
// count for the executed instruction(s) to complete.
if (ii->isEndOfKernel()) {
// Waiting for older instruction to execute
if (w->instructionBuffer.front()->seqNum() != ii->seqNum()) {
*rdyStatus = NRDY_WAIT_CNT;
return false;
}
// Older instructions have executed, adding implicit wait count
w->setStatus(Wavefront::S_WAITCNT);
w->setWaitCnts(0, 0, 0);
if (!w->waitCntsSatisfied()) {
*rdyStatus = NRDY_WAIT_CNT;
return false;
}
}
DPRINTF(GPUExec, "CU%d: WF[%d][%d]: Ready Inst : %s\n", computeUnit.cu_id,
w->simdId, w->wfSlotId, ii->disassemble());
*exeResType = mapWaveToExeUnit(w);
*rdyStatus = INST_RDY;
return true;
}
int
ScoreboardCheckStage::mapWaveToExeUnit(Wavefront *w)
{
GPUDynInstPtr ii = w->nextInstr();
assert(ii);
if (ii->isFlat()) {
/**
* NOTE: Flat memory ops requires both GM and LM resources.
* The simulator models consumption of both GM and LM
* resources in the schedule stage. At instruction execution time,
* after the aperture check is performed, only the GM or LM pipe
* is actually reserved by the timing model. The GM unit is returned
* here since Flat ops occupy the GM slot in the ready and dispatch
* lists. They also consume the LM slot in the dispatch list.
*/
return w->globalMem;
} else if (ii->isLocalMem()) {
return w->localMem;
} else if (ii->isGlobalMem()) {
if (!ii->isScalar()) {
return w->globalMem;
} else {
return w->scalarMem;
}
} else if (ii->isBranch() ||
ii->isALU() ||
(ii->isKernArgSeg() && ii->isLoad()) ||
ii->isArgSeg() ||
ii->isReturn() ||
ii->isEndOfKernel() ||
ii->isNop() ||
ii->isBarrier()) {
if (!ii->isScalar()) {
return w->simdId;
} else {
return w->scalarAluGlobalIdx;
}
}
panic("%s: unmapped to an execution resource", ii->disassemble());
return computeUnit.numExeUnits();
}
void
ScoreboardCheckStage::exec()
{
/**
* Reset the ready list for all execution units; ready list will be
* constructed every cycle because resource availability may change.
*/
toSchedule.reset();
// Iterate over all WF slots across all SIMDs.
for (int simdId = 0; simdId < computeUnit.numVectorALUs; ++simdId) {
for (int wfSlot = 0; wfSlot < computeUnit.shader->n_wf; ++wfSlot) {
// reset the ready status of each wavefront
Wavefront *curWave = computeUnit.wfList[simdId][wfSlot];
nonrdytype_e rdyStatus = NRDY_ILLEGAL;
int exeResType = -1;
// check WF readiness: If the WF's oldest
// instruction is ready to issue then add the WF to the ready list
if (ready(curWave, &rdyStatus, &exeResType, wfSlot)) {
assert(curWave->simdId == simdId);
DPRINTF(GPUSched,
"Adding to readyList[%d]: SIMD[%d] WV[%d]: %d: %s\n",
exeResType,
curWave->simdId, curWave->wfDynId,
curWave->nextInstr()->seqNum(),
curWave->nextInstr()->disassemble());
toSchedule.markWFReady(curWave, exeResType);
}
collectStatistics(rdyStatus);
}
}
}
ScoreboardCheckStage::
ScoreboardCheckStageStats::ScoreboardCheckStageStats(statistics::Group *parent)
: statistics::Group(parent, "ScoreboardCheckStage"),
ADD_STAT(stallCycles, "number of cycles wave stalled in SCB")
{
stallCycles.init(NRDY_CONDITIONS);
stallCycles.subname(NRDY_WF_STOP, csprintf("WFStop"));
stallCycles.subname(NRDY_IB_EMPTY, csprintf("IBEmpty"));
stallCycles.subname(NRDY_WAIT_CNT, csprintf("WaitCnt"));
stallCycles.subname(NRDY_BARRIER_WAIT, csprintf("BarrierWait"));
stallCycles.subname(NRDY_VGPR_NRDY, csprintf("VgprBusy"));
stallCycles.subname(NRDY_SGPR_NRDY, csprintf("SgprBusy"));
stallCycles.subname(INST_RDY, csprintf("InstrReady"));
}
} // namespace gem5