provide first draft of implementations for the cachers functionality

offloading-cacher/offloading-cache.hpp

@@ -4,9 +4,11 @@
 #include <vector>
 #include <thread>
 #include <unordered_map>
+#include <shared_mutex>
 
 #include <semaphore.h>
 
+#include <sched.h>
 #include <numa.h>
 
 #include <dml/dml.hpp>
@@ -28,13 +30,6 @@ namespace offcache {
         Relaxed, Immediate, ImmediateNoCache
     };
 
-    struct WorkerTask {
-        uint8_t* src_;
-        uint8_t* dst_;
-        size_t size_;
-        std::atomic<bool> completed_ { false };
-    };
-
     // the cache task structure will be used to submit and
     // control a cache element, while providing source pointer
     // and size in bytes for submission
@@ -45,26 +40,11 @@ namespace offcache {
     struct CacheTask {
         uint8_t* data_;
         size_t size_;
-        ExecutionPolicy policy_;
-        uint8_t* result_;
-        std::atomic<bool> active_;
-        std::vector<WorkerTask> sub_tasks_;
-    };
-
-    // worker class, one for each numa node
-    // discovers its node configuration on startup
-    // and keeps track of available memory
-    class CacheWorker {
-    public:
-        uint8_t numa_node_ = 0;
-
-        // this is the mailbox of the worker to which a new task
-        // may be submitted by exchanging nullptr with a valid one
-        // and notifying on the atomic after which ownership
-        // of the CacheTask structure is transferred to the worker
-        std::atomic<WorkerTask*>* task_slot_ = nullptr;
-
-        static void run(CacheWorker* this_);
+        uint8_t* result_ = nullptr;
+        uint8_t* maybe_result_ = nullptr;
+        std::atomic<bool> active_ { true };
+        std::atomic<bool> valid_ { false };
+        std::vector<dml::handler<dml::mem_copy_operation, std::allocator<uint8_t>>> handlers_;
     };
 
     // singleton which holds the cache workers
@@ -77,71 +57,283 @@ namespace offcache {
         // return optimal cache placement
         // dst node and returned value can differ if the system, for example, has HBM
         // attached accessible directly to node n under a different node id m
-        typedef uint8_t (CachePolicy)(const uint8_t numa_dst_node, const uint8_t numa_src_node, const size_t data_size);
+        typedef int (CachePolicy)(const int numa_dst_node, const int numa_src_node, const size_t data_size);
 
         // copy policy specifies the copy-executing nodes for a given task
         // which allows flexibility in assignment for optimizing raw throughput
         // or choosing a conservative usage policy
-        typedef std::vector<uint8_t> (CopyPolicy)(const uint8_t numa_dst_node, const uint8_t numa_src_node);
+        typedef std::vector<int> (CopyPolicy)(const int numa_dst_node, const int numa_src_node);
 
     private:
-        std::unordered_map<uint8_t, CacheWorker> workers_;
+        std::shared_mutex cache_mutex_;
 
         std::unordered_map<uint8_t*, CacheTask*> cache_state_;
 
         CachePolicy* cache_policy_function_ = nullptr;
         CopyPolicy* copy_policy_function_ = nullptr;
 
+        dml::handler<dml::mem_copy_operation, std::allocator<uint8_t>> ExecuteCopy(const uint8_t* src, uint8_t* dst, const size_t size, const int node) const;
+
+        void SubmitTask(CacheTask* task);
+
+        CacheTask* CreateTask(const uint8_t *data, const size_t size) const;
+
+        void DestroyTask(CacheTask* task) const;
+
     public:
         void Init(CachePolicy* cache_policy_function, CopyPolicy* copy_policy_function);
 
-        // submits the given task and takes ownership of the pointer
-        void SubmitTask(CacheTask* task, const ExecutionPolicy policy) const;
+        // function to perform data access through the cache
+        // behaviour depends on the chosen execution policy
+        // Immediate and ImmediateNoCache return a cache task
+        // with guaranteed-valid result value where Relaxed
+        // policy does not come with this guarantee.
+        CacheTask* Access(uint8_t* data, const size_t size, const ExecutionPolicy policy);
 
         // waits upon completion of caching
-        // returns the location of the data
-        static uint8_t* WaitOnCompletion(CacheTask* task);
+        static void WaitOnCompletion(CacheTask* task);
 
         // invalidates the given pointer
+        // afterwards the reference to the
+        // cache task object may be forgotten
         static void SignalDataUnused(CacheTask* task);
-    };
-}
 
-void offcache::CacheWorker::run(CacheWorker* this_) {
+        // returns the location of the cached data
+        // which may or may not be valid
+        static uint8_t* GetDataLocation(CacheTask* task);
 
+        void Flush();
+    };
 }
 
-void offcache::CacheCoordinator::Init(CachePolicy* cache_policy_function, CopyPolicy* copy_policy_function) {
+inline void offcache::CacheCoordinator::Init(CachePolicy* cache_policy_function, CopyPolicy* copy_policy_function) {
     cache_policy_function_ = cache_policy_function;
     copy_policy_function_ = copy_policy_function;
 
     // initialize numa library
     numa_available();
+}
+
+inline offcache::CacheTask* offcache::CacheCoordinator::Access(uint8_t* data, const size_t size, const ExecutionPolicy policy) {
+    // the best situation is if this data is already cached
+    // which we check in an unnamed block in which the cache
+    // is locked for reading to prevent another thread
+    // from marking the element we may find as unused and
+    // clearing it
+    {
+        std::shared_lock<std::shared_mutex> lock(cache_mutex_);
 
-    const uint8_t nodes_max = numa_num_configured_nodes();
-    const uint8_t valid_nodes = numa_get_mems_allowed();
+        const auto search = cache_state_.find(data);
 
-    for (uint8_t node = 0; node < nodes_max; node++) {
-        if (numa_bitmask_isbitset(valid_nodes, node)) {
-            workers_.insert({ node, CacheWorker() });
-            workers_[node].numa_node_ = node;
-            std::thread t (CacheWorker::run, &workers_[node]);
-            t.detach();
+        if (search != cache_state_.end()) {
+            if (search->second->size_ == size) {
+                search->second->active_.store(true);
+                // TODO: check for completed status depending on execution policy
+                return search->second;
+            }
+            else {
+                DestroyTask(search->second);
+                cache_state_.erase(search);
+            }
         }
     }
+
+    // at this point the requested data is not present in cache
+    // and we create a caching task for it
+
+    CacheTask* task = CreateTask(data, size);
+
+    if (policy == ExecutionPolicy::Immediate) {
+        // in intermediate mode the returned task
+        // object is guaranteed to be valid and therefore
+        // its resulting location must be validated
+        // after which we submit the task
+        // maybe_result is then set by submit
+
+        task->result_ = data;
+        SubmitTask(task);
+        return task;
+    }
+    else if (policy == ExecutionPolicy::ImmediateNoCache) {
+        // for immediatenocache we just validate
+        // the generated task and return it
+        // we must also set maybe_result in case
+        // someone waits on this
+
+        task->result_ = data;
+        task->maybe_result_ = data;
+        return task;
+    }
+    else if (policy == ExecutionPolicy::Relaxed) {
+        // for relaxed no valid task must be returned
+        // and therefore we just submit and then give
+        // the possible invalid task back with only
+        // maybe_result set by submission
+        
+        SubmitTask(task);
+        return task;
+    }
+    else {
+        // this should not be reached
+    }
 }
 
-void offcache::CacheCoordinator::SubmitTask(CacheTask* task, const ExecutionPolicy policy) const {
+inline void offcache::CacheCoordinator::SubmitTask(CacheTask* task) {
+    // obtain numa node of current thread to determine where the data is needed
+
+    const int current_cpu = sched_getcpu();
+    const int current_node = numa_node_of_cpu(current_cpu);
+
+    // obtain node that the given data pointer is allocated on
+
+    int data_node = -1;
+    get_mempolicy(&data_node, NULL, 0, (void*)task->data_, MPOL_F_NODE | MPOL_F_ADDR);
+
+    // querry cache policy function for the destination numa node
+
+    const uint32_t dst_node = cache_policy_function_(current_node, data_node, task->size_);
+
+    // allocate data on this node and flush the unused parts of the
+    // cache if the operation fails and retry once
+    // TODO: smarter flush strategy could keep some stuff cached
+
+    uint8_t* dst = numa_alloc_onnode(task->size_, dst_node);
+
+    if (dst == nullptr) {
+        Flush();
+
+        dst = numa_alloc_onnode(task->size_, dst_node);
+
+        if (dst == nullptr) {
+            return;
+        }
+    }
+
+    task->maybe_result_ = dst;
 
+    // querry copy policy function for the nodes to use for the copy
+
+    const std::vector<int> executing_nodes = copy_policy_function_(dst_node, data_node);
+    const size_t task_count = executing_nodes.size();
+
+    // at this point the task may be added to the cache structure
+    // due to the task being initialized with the valid flag set to false
+
+    {
+        std::unique_lock<std::shared_mutex> lock(cache_mutex_);
+
+        const auto state = cache_state_.insert({task->data_, task});
+
+        // if state.second is false then no insertion took place
+        // which means that concurrently whith this thread
+        // some other thread must have accessed the same
+        // resource in which case we must perform an abort
+        // TODO: abort is not the only way to handle this situation
+
+        if (!state.second) {
+            // abort by doing the following steps
+            // (1) free the allocated memory, (2) remove the "maybe result" as
+            // we will not run the caching operation, (3) clear the sub tasks
+            // for the very same reason, (4) set the result to the RAM-location
+
+            numa_free(dst, task->size_);
+            task->maybe_result_ = nullptr;
+            task->result_ = task->data_;
+            return;
+        }
+    }
+
+    // each task will copy one fair part of the total size
+    // and in case the total size is not a factor of the
+    // given task count the last node must copy the remainder
+
+    const size_t size = task->size_ / task_count;
+    const size_t last_size = size + task->size_ % task_count;
+
+    // save the current numa node mask to restore later
+    // as executing the copy task will place this thread
+    // on a different node
+
+    const int nodemask = numa_get_run_node_mask();
+
+    for (uint32_t i = 0; i < task_count; i++) {
+        const size_t local_size = i + 1 == task_count ? size : last_size;
+        const size_t local_offset = i * size;
+        const uint8_t* local_src = task->data_ + local_offset; 
+        uint8_t* local_dst = dst + local_offset;
+
+        const auto handler = ExecuteCopy(local_src, local_dst, local_size, executing_nodes[i]);
+        task->handlers_.emplace_back(handler);
+    }
+
+    // set the valid flag of the task as all handlers
+    // required for completion signal are registered
+
+    task->valid_.store(true);
+    task->valid_.notify_all();
+
+    // restore the previous nodemask
+
+    numa_run_on_node_mask(nodemask);
 }
 
-uint8_t* offcache::CacheCoordinator::WaitOnCompletion(CacheTask* task) {
-    while (!task->sub_tasks_.empty()) {
-        task->sub_tasks_.back().completed_.wait(false);
-        task->sub_tasks_.pop_back();
+inline dml::handler<dml::mem_copy_operation, std::allocator<uint8_t>> offcache::CacheCoordinator::ExecuteCopy(const uint8_t* src, uint8_t* dst, const size_t size, const int node) {
+    dml::data_view srcv = dml::make_view(reinterpret_cast<uint8_t*>(src), size);
+    dml::data_view dstv = dml::make_view(reinterpret_cast<uint8_t*>(dst), size);
+
+    numa_run_on_node(node);
+
+    return dml::submit<path>(dml::mem_copy.block_on_fault(), srcv, dstv);
+}
+
+inline offcache::CacheTask* offcache::CacheCoordinator::CreateTask(const uint8_t* data, const size_t size) const {
+    CacheTask* task = new CacheTask();
+    task->data_ = data;
+    task->size_ = size;
+    return task;
+}
+
+inline void offcache::CacheCoordinator::DestroyTask(CacheTask* task) const {
+    numa_free(task->result_, task->size_);
+    delete task;
+}
+
+inline void offcache::CacheCoordinator::WaitOnCompletion(CacheTask* task) {
+    task->valid_.wait(false);
+
+    for (auto& handler : task->handlers_) {
+        auto result = handler.get();
+        // TODO: handle the returned status code
     }
+
+    task->handlers_.clear();
 }
 
-void offcache::CacheCoordinator::SignalDataUnused(CacheTask* task) {
+inline uint8_t* offcache::CacheCoordinator::GetDataLocation(CacheTask* task) {
+    return task->result_;
+}
+
+inline void offcache::CacheCoordinator::SignalDataUnused(CacheTask* task) {
     task->active_.store(false);
 }
+
+inline void offcache::CacheCoordinator::Flush() {
+    // TODO: there probably is a better way to implement this flush
+
+    {
+        std::unique_lock<std::shared_mutex> lock(cache_mutex_);
+        
+        auto it = cache_state_.begin();
+
+        while (it != cache_state_.end()) {
+            if (it->second->active_.load() == false) {
+                DestroyTask(it->second);
+                cache_state_.erase(it);
+                it = cache_state_.begin();
+            }
+            else {
+                it++;
+            }
+        }
+    }
+}