gpu-compute: support in-order data delivery in GM pipe

this patch adds an ordered response buffer to the GM pipeline
to ensure in-order data delivery. the buffer is implemented as
a stl ordered map, which sorts the request in program order by
using their sequence ID. when requests return to the GM pipeline
they are marked as done. only the oldest request may be serviced
from the ordered buffer, and only if is marked as done.

the FIFO response buffers are kept and used in OoO delivery mode

1 files changed, 48 insertions, 1 deletions

diff --git a/src/gpu-compute/global_memory_pipeline.hh b/src/gpu-compute/global_memory_pipeline.hh
index 368a15079..d10b7c1a2 100644
--- a/src/gpu-compute/global_memory_pipeline.hh
+++ b/src/gpu-compute/global_memory_pipeline.hh
@@ -62,10 +62,40 @@ class GlobalMemPipeline
     void init(ComputeUnit *cu);
     void exec();
 
-    std::queue<GPUDynInstPtr> &getGMReqFIFO() { return gmIssuedRequests; }
     std::queue<GPUDynInstPtr> &getGMStRespFIFO() { return gmReturnedStores; }
     std::queue<GPUDynInstPtr> &getGMLdRespFIFO() { return gmReturnedLoads; }
 
+    /**
+     * find the next ready response to service. for OoO mode we
+     * simply pop the oldest (based on when the response was
+     * received) response in the response FIFOs. for in-order mode
+     * we pop the oldest (in program order) response, and only if
+     * it is marked as done.
+     */
+    GPUDynInstPtr getNextReadyResp();
+
+    /**
+     * once a memory request is finished we remove it from the
+     * buffer. this method determines which response buffer
+     * we're using based on the mode (in-order vs. OoO).
+     */
+    void completeRequest(GPUDynInstPtr gpuDynInst);
+
+    /**
+     * issues a request to the pipeline - i.e., enqueue it
+     * in the request buffer.
+     */
+    void issueRequest(GPUDynInstPtr gpuDynInst);
+
+    /**
+     * this method handles responses sent to this GM pipeline by the
+     * CU. in the case of in-order delivery it simply marks the reqeust
+     * as done in the ordered buffer to indicate that the requst is
+     * finished. for out-of-order data delivery, the requests are enqueued
+     * (in the order in which they are received) in the response FIFOs.
+     */
+    void handleResponse(GPUDynInstPtr gpuDynInst);
+
     bool
     isGMLdRespFIFOWrRdy() const
     {
@@ -97,6 +127,7 @@ class GlobalMemPipeline
     ComputeUnit *computeUnit;
     std::string _name;
     int gmQueueSize;
+    bool outOfOrderDataDelivery;
 
     // number of cycles of delaying the update of a VGPR that is the
     // target of a load instruction (or the load component of an atomic)
@@ -111,6 +142,22 @@ class GlobalMemPipeline
     // The size of global memory.
     int globalMemSize;
 
+    /*
+     * this buffer holds the memory responses when in-order data
+     * deilvery is used - the responses are ordered by their unique
+     * sequence number, which is monotonically increasing. when a
+     * memory request returns its "done" flag is set to true. during
+     * each tick the the GM pipeline will check if the oldest request
+     * is finished, and if so it will be removed from the queue.
+     *
+     * key:   memory instruction's sequence ID
+     *
+     * value: pair holding the instruction pointer and a bool that
+     *        is used to indicate whether or not the request has
+     *        completed
+     */
+    std::map<uint64_t, std::pair<GPUDynInstPtr, bool>> gmOrderedRespBuffer;
+
     // Global Memory Request FIFO: all global memory requests
     // are issued to this FIFO from the memory pipelines
     std::queue<GPUDynInstPtr> gmIssuedRequests;