gpu-compute: Added method to compute the actual workgroup size

This patch adds a method to the Wavefront class to compute the actual workgroup
size. This can be different from the maximum workgroup size specified when
launching the kernel through the NDRange object. Current solution is still not
optimal, as we are computing these for each wavefront and the dispatcher also
needs to have this information and can't actually call
Wavefront::computeActuallWgSz before the wavefronts are being created. A long
term solution would be to have a Workgroup class that deals with all these
details.

src/gpu-compute/compute_unit.cc

@@ -174,7 +174,7 @@ ComputeUnit::~ComputeUnit()
 }
 
 void
-ComputeUnit::FillKernelState(Wavefront *w, NDRange *ndr)
+ComputeUnit::fillKernelState(Wavefront *w, NDRange *ndr)
 {
     w->resizeRegFiles(ndr->q.cRegCount, ndr->q.sRegCount, ndr->q.dRegCount);
 
@@ -190,6 +190,7 @@ ComputeUnit::FillKernelState(Wavefront *w, NDRange *ndr)
     w->spillSizePerItem = ndr->q.spillMemPerItem;
     w->roBase = ndr->q.roMemStart;
     w->roSize = ndr->q.roMemTotal;
+    w->computeActualWgSz(ndr);
 }
 
 void
@@ -220,19 +221,16 @@ ComputeUnit::updateEvents() {
 
 
 void
-ComputeUnit::StartWF(Wavefront *w, int trueWgSize[], int trueWgSizeTotal,
-                     int waveId, LdsChunk *ldsChunk, NDRange *ndr)
+ComputeUnit::startWavefront(Wavefront *w, int waveId, LdsChunk *ldsChunk,
+                            NDRange *ndr)
 {
     static int _n_wave = 0;
 
-    // Fill in Kernel state
-    FillKernelState(w, ndr);
-
     VectorMask init_mask;
     init_mask.reset();
 
     for (int k = 0; k < wfSize(); ++k) {
-        if (k + waveId * wfSize() < trueWgSizeTotal)
+        if (k + waveId * wfSize() < w->actualWgSzTotal)
             init_mask[k] = 1;
     }
 
@@ -241,18 +239,18 @@ ComputeUnit::StartWF(Wavefront *w, int trueWgSize[], int trueWgSizeTotal,
     w->initMask = init_mask.to_ullong();
 
     for (int k = 0; k < wfSize(); ++k) {
-        w->workItemId[0][k] = (k + waveId * wfSize()) % trueWgSize[0];
-        w->workItemId[1][k] =
-            ((k + waveId * wfSize()) / trueWgSize[0]) % trueWgSize[1];
-        w->workItemId[2][k] =
-            (k + waveId * wfSize()) / (trueWgSize[0] * trueWgSize[1]);
+        w->workItemId[0][k] = (k + waveId * wfSize()) % w->actualWgSz[0];
+        w->workItemId[1][k] = ((k + waveId * wfSize()) / w->actualWgSz[0]) %
+                             w->actualWgSz[1];
+        w->workItemId[2][k] = (k + waveId * wfSize()) /
+                              (w->actualWgSz[0] * w->actualWgSz[1]);
 
-        w->workItemFlatId[k] = w->workItemId[2][k] * trueWgSize[0] *
-            trueWgSize[1] + w->workItemId[1][k] * trueWgSize[0] +
+        w->workItemFlatId[k] = w->workItemId[2][k] * w->actualWgSz[0] *
+            w->actualWgSz[1] + w->workItemId[1][k] * w->actualWgSz[0] +
             w->workItemId[0][k];
     }
 
-    w->barrierSlots = divCeil(trueWgSizeTotal, wfSize());
+    w->barrierSlots = divCeil(w->actualWgSzTotal, wfSize());
 
     w->barCnt.resize(wfSize(), 0);
 
@@ -294,8 +292,8 @@ ComputeUnit::StartWF(Wavefront *w, int trueWgSize[], int trueWgSizeTotal,
     // is this the last wavefront in the workgroup
     // if set the spillWidth to be the remaining work-items
     // so that the vector access is correct
-    if ((waveId + 1) * wfSize() >= trueWgSizeTotal) {
-        w->spillWidth = trueWgSizeTotal - (waveId * wfSize());
+    if ((waveId + 1) * wfSize() >= w->actualWgSzTotal) {
+        w->spillWidth = w->actualWgSzTotal - (waveId * wfSize());
     } else {
         w->spillWidth = wfSize();
     }
@@ -328,17 +326,6 @@ ComputeUnit::StartWorkgroup(NDRange *ndr)
         injectGlobalMemFence(gpuDynInst, true);
     }
 
-    // Get true size of workgroup (after clamping to grid size)
-    int trueWgSize[3];
-    int trueWgSizeTotal = 1;
-
-    for (int d = 0; d < 3; ++d) {
-        trueWgSize[d] = std::min(ndr->q.wgSize[d], ndr->q.gdSize[d] -
-                                 ndr->wgId[d] * ndr->q.wgSize[d]);
-
-        trueWgSizeTotal *= trueWgSize[d];
-    }
-
     // calculate the number of 32-bit vector registers required by wavefront
     int vregDemand = ndr->q.sRegCount + (2 * ndr->q.dRegCount);
     int wave_id = 0;
@@ -350,9 +337,10 @@ ComputeUnit::StartWorkgroup(NDRange *ndr)
         // It must be stopped and not waiting
         // for a release to complete S_RETURNING
         if (w->status == Wavefront::S_STOPPED) {
+            fillKernelState(w, ndr);
             // if we have scheduled all work items then stop
             // scheduling wavefronts
-            if (wave_id * wfSize() >= trueWgSizeTotal)
+            if (wave_id * wfSize() >= w->actualWgSzTotal)
                 break;
 
             // reserve vector registers for the scheduled wavefront
@@ -365,7 +353,7 @@ ComputeUnit::StartWorkgroup(NDRange *ndr)
             w->reservedVectorRegs = normSize;
             vectorRegsReserved[m % numSIMDs] += w->reservedVectorRegs;
 
-            StartWF(w, trueWgSize, trueWgSizeTotal, wave_id, ldsChunk, ndr);
+            startWavefront(w, wave_id, ldsChunk, ndr);
             ++wave_id;
         }
     }

src/gpu-compute/compute_unit.hh

@@ -254,10 +254,10 @@ class ComputeUnit : public MemObject
     void exec();
     void initiateFetch(Wavefront *wavefront);
     void fetch(PacketPtr pkt, Wavefront *wavefront);
-    void FillKernelState(Wavefront *w, NDRange *ndr);
+    void fillKernelState(Wavefront *w, NDRange *ndr);
 
-    void StartWF(Wavefront *w, int trueWgSize[], int trueWgSizeTotal,
-                     int cnt, LdsChunk *ldsChunk, NDRange *ndr);
+    void startWavefront(Wavefront *w, int waveId, LdsChunk *ldsChunk,
+                        NDRange *ndr);
 
     void StartWorkgroup(NDRange *ndr);
     int ReadyWorkgroup(NDRange *ndr);

src/gpu-compute/wavefront.cc

@@ -1066,3 +1066,14 @@ Wavefront::setContext(const void *in)
             ldsChunk->write<char>(i, val);
         }
 }
+
+void
+Wavefront::computeActualWgSz(NDRange *ndr)
+{
+    actualWgSzTotal = 1;
+    for (int d = 0; d < 3; ++d) {
+        actualWgSz[d] = std::min(workGroupSz[d],
+                                 gridSz[d] - ndr->wgId[d] * workGroupSz[d]);
+        actualWgSzTotal *= actualWgSz[d];
+    }
+}

src/gpu-compute/wavefront.hh

@@ -47,6 +47,7 @@
 #include "gpu-compute/condition_register_state.hh"
 #include "gpu-compute/lds_state.hh"
 #include "gpu-compute/misc.hh"
+#include "gpu-compute/ndrange.hh"
 #include "params/Wavefront.hh"
 #include "sim/sim_object.hh"
 
@@ -189,11 +190,16 @@ class Wavefront : public SimObject
     std::vector<Addr> lastAddr;
     std::vector<uint32_t> workItemId[3];
     std::vector<uint32_t> workItemFlatId;
+    /* kernel launch parameters */
     uint32_t workGroupId[3];
     uint32_t workGroupSz[3];
     uint32_t gridSz[3];
     uint32_t wgId;
     uint32_t wgSz;
+    /* the actual WG size can differ than the maximum size */
+    uint32_t actualWgSz[3];
+    uint32_t actualWgSzTotal;
+    void computeActualWgSz(NDRange *ndr);
     // wavefront id within a workgroup
     uint32_t wfId;
     uint32_t maxDynWaveId;