bachelor-thesis/offloading-cacher/offloading-cache.hpp

#pragma once

#include <atomic>
#include <vector>
#include <unordered_map>

#include <numa.h>

#include <dml/dml.hpp>

namespace offcache {
    // the cache task structure will be used to submit and
    // control a cache element, while providing source pointer
    // and size in bytes for submission
    //
    // then the submitting thread may wait on the atomic "result"
    // which will be notified by the cache worker upon processing
    // after which the atomic-bool-ptr active will also become valid
    // 
    // the data pointed to by result and the bool-ptr are guaranteed
    // to remain valid until the value pointed to by active is changed
    // to false, after which the worker may clean up and delete the
    // structure - carefull, do not call delete on this, the worker does
    struct CacheTask {
        uint8_t* data_;
        size_t size_;
        std::atomic<uint8_t*> result_ { nullptr };
        std::atomic<bool>* active_;
    };

    // worker class, one for each numa node
    // discovers its node configuration on startup
    // and keeps track of available memory
    class CacheWorker {
    private:
        uint8_t numa_node_ = 0;

        std::unordered_map<uint8_t*, CacheTask*> cache_info_;

    public:
        // 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<CacheTask*>* task_slot_ = nullptr;

        static void run(CacheWorker* this_, const uint8_t numa_node);
    };

    // singleton which holds the cache workers
    // and is the place where work will be submited
    class CacheCoordinator {
    public:
        // cache policy is defined as a type here to allow flexible usage of the cacher
        // given a numa destination node (where the data will be needed), the numa source
        // node (current location of the data) and the data size, this function should
        // 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);

        // 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);

        enum class ExecutionPolicy {
            Immediate, Relaxed, NoCache
        };

    private:
        CachePolicy* cache_policy_function_ = nullptr;
        CopyPolicy* copy_policy_function_ = nullptr;

    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;

        static void WaitOnCompletion(CacheTask* task);
        static void SignalDataUnused(CacheTask* task);
    };
}