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#pragma once
#include <iostream>
#include <unordered_map>
#include <shared_mutex>
#include <mutex>
#include <memory>
#include <sched.h>
#include <numa.h>
#include <numaif.h>
#include <dml/dml.hpp>
namespace dml { inline const std::string StatusCodeToString(const dml::status_code code) { switch (code) { case dml::status_code::ok: return "ok"; case dml::status_code::false_predicate: return "false predicate"; case dml::status_code::partial_completion: return "partial completion"; case dml::status_code::nullptr_error: return "nullptr error"; case dml::status_code::bad_size: return "bad size"; case dml::status_code::bad_length: return "bad length"; case dml::status_code::inconsistent_size: return "inconsistent size"; case dml::status_code::dualcast_bad_padding: return "dualcast bad padding"; case dml::status_code::bad_alignment: return "bad alignment"; case dml::status_code::buffers_overlapping: return "buffers overlapping"; case dml::status_code::delta_delta_empty: return "delta delta empty"; case dml::status_code::batch_overflow: return "batch overflow"; case dml::status_code::execution_failed: return "execution failed"; case dml::status_code::unsupported_operation: return "unsupported operation"; case dml::status_code::queue_busy: return "queue busy"; case dml::status_code::error: return "unknown error"; case dml::status_code::config_error: return "config error"; default: return "unhandled error"; } } }
namespace dsacache { class Cache;
/*
* Class Description: * Holds all required information on one cache entry and is used * both internally by the Cache and externally by the user. * * Important Usage Notes: * The pointer is only updated in WaitOnCompletion() which * therefore must be called by the user at some point in order * to use the cached data. Using this class as T for * std::shared_ptr<T> is not recommended as references are * already counted internally. * * Cache Lifetime: * As long as the instance is referenced, the pointer it stores * is guaranteed to be either nullptr or pointing to a valid copy. * * Implementation Detail: * Performs self-reference counting with a shared atomic integer. * Therefore on creating a copy the reference count is increased * and with the destructor it is deacresed. If the last copy is * destroyed the actual underlying data is freed and all shared * variables deleted. * * Notes on Thread Safety: * Class is thread safe in any possible state and performs * reference counting and deallocation itself entirely atomically. */
class CacheData { public: using dml_handler = dml::handler<dml::mem_copy_operation, std::allocator<uint8_t>>;
private: // data source and size of the block
uint8_t* src_; size_t size_;
// global reference counting object
std::atomic<int32_t>* active_;
// global cache-location pointer
std::atomic<uint8_t*>* cache_;
// object-local incomplete cache location pointer
// which is only available in the first instance
uint8_t* incomplete_cache_;
// dml handler vector pointer which is only
// available in the first instance
std::unique_ptr<std::vector<dml_handler>> handlers_;
// deallocates the global cache-location
// and invalidates it
void Deallocate();
// checks whether there are at least two
// valid references to this object which
// is done as the cache always has one
// internally to any living instance
bool Active() const;
friend Cache;
public: CacheData(uint8_t* data, const size_t size); CacheData(const CacheData& other); ~CacheData();
// waits on completion of caching operations
// for this task and is safe to be called in
// any state of the object
void WaitOnCompletion();
// returns the cache data location for this
// instance which is valid as long as the
// instance is alive - !!! this may also
// yield a nullptr !!!
uint8_t* GetDataLocation() const; };
/*
* Class Description: * Class will handle access to data through internal copies. * These are obtained via work submission to the Intel DSA which takes * care of asynchronously duplicating the data. The user will define * where these copies lie and which system nodes will perform the copy. * This is done through policy functions set during initialization. * * Placement Policy: * The Placement Policy Function decides on which node a particular * entry is to be placed, given the current executing node and the * data source node and data size. This in turn means that for one * datum, multiple cached copies may exist at one time. * * Cache Lifetime: * When accessing the cache, a CacheData-object will be returned. * As long as this object lives, the pointer which it holds is * guaranteed to be either nullptr or a valid copy. When destroyed * the entry is marked for deletion which is only carried out * when system memory pressure drives an automated cache flush. * * Restrictions: * - Overlapping Pointers may lead to undefined behaviour during * manual cache invalidation which should not be used if you * intend to have these types of pointers * - Cache Invalidation may only be performed manually and gives * no ordering guarantees. Therefore, it is the users responsibility * to ensure that results after invalidation have been generated * using the latest state of data. The cache is best suited * to static data. * * Notes on Thread Safety: * - Cache is completely thread-safe after initialization * - CacheData-class will handle deallocation of data itself by * performing self-reference-counting atomically and only * deallocating if the last reference is destroyed * - The internal cache state has one lock which is either * acquired shared for reading the state (upon accessing an already * cached element) or unique (accessing a new element, flushing, invalidating) * - Waiting on copy completion is done over an atomic-wait in copies * of the original CacheData-instance * - Overall this class may experience performance issues due to the use * of locking (in any configuration), lock contention (worsens with higher * core count, node count and utilization) and atomics (worse in the same * situations as lock contention) * * Improving Performance: * When data is never shared between threads or memory size for the cache is * not an issue you may consider having one Cache-instance per thread and removing * the lock in Cache and modifying the reference counting and waiting mechanisms * of CacheData accordingly (although this is high effort and will yield little due * to the atomics not being shared among cores/nodes). * Otherwise, one Cache-instance per node could also be considered. This will allow * the placement policy function to be barebones and reduces the lock contention and * synchronization impact of the atomic variables. */
class Cache { 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 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<int> (CopyPolicy)(const int numa_dst_node, const int numa_src_node, const size_t data_size);
private: // mutex for accessing the cache state map
std::shared_mutex cache_mutex_;
// map from [dst-numa-node,map2]
// map2 from [data-ptr,cache-structure]
std::unordered_map<uint8_t, std::unordered_map<uint8_t*, CacheData>> cache_state_;
CachePolicy* cache_policy_function_ = nullptr; CopyPolicy* copy_policy_function_ = nullptr;
// function used to submit a copy task on a specific node to the dml
// engine on that node - will change the current threads node assignment
// to achieve this so take care to restore this
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;
// allocates the required memory on the destination node
// and then submits task to the dml library for processing
// and attaches the handlers to the cache data structure
void SubmitTask(CacheData* task, const int dst_node, const int src_node);
// querries the policy functions for the given data and size
// to obtain destination cache node, also returns the datas
// source node for further usage
// output may depend on the calling threads node assignment
// as this is set as the "optimal placement" node
void GetCacheNode(uint8_t* src, const size_t size, int* OUT_DST_NODE, int* OUT_SRC_NODE) const;
// allocates memory of size "size" on the numa node "node"
// and returns nullptr if this is not possible, also may
// try to flush the cache of the requested node to
// alleviate encountered shortage
uint8_t* AllocOnNode(const size_t size, const int node);
// checks whether the cache contains an entry for
// the given data in the given memory node and
// returns it, otherwise returns nullptr
std::unique_ptr<CacheData> GetFromCache(uint8_t* src, const size_t size, const int dst_node);
public: Cache(const Cache& other) = delete;
// initializes the cache with the two policy functions
// only after this is it safe to use in a threaded environment
void Init(CachePolicy* cache_policy_function, CopyPolicy* copy_policy_function);
// function to perform data access through the cache
std::unique_ptr<CacheData> Access(uint8_t* data, const size_t size);
// flushes the cache of inactive entries
// if node is -1 then the whole cache is
// checked and otherwise the specified
// node - no checks on node validity
void Flush(const int node = -1);
// forces out all entries from the
// cache and therefore will also "forget"
// still-in-use entries, these will still
// be properly deleted, but the cache
// will be fresh - use for testing
void Clear();
void Invalidate(uint8_t* data); }; }
inline void dsacache::Cache::Clear() { std::unique_lock<std::shared_mutex> lock(cache_mutex_);
cache_state_.clear();
Init(cache_policy_function_, copy_policy_function_); }
inline void dsacache::Cache::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();
// obtain all available nodes
// and those we may allocate
// memory on
const int nodes_max = numa_num_configured_nodes(); const bitmask* valid_nodes = numa_get_mems_allowed();
// prepare the cache state with entries
// for all given nodes
for (int node = 0; node < nodes_max; node++) { if (numa_bitmask_isbitset(valid_nodes, node)) { cache_state_.insert({node,{}}); } } }
inline std::unique_ptr<dsacache::CacheData> dsacache::Cache::Access(uint8_t* data, const size_t size) { // get destination numa node for the cache
int dst_node = -1; int src_node = -1;
GetCacheNode(data, size, &dst_node, &src_node);
// TODO: at this point it could be beneficial to check whether
// TODO: the given destination node is present as an entry
// TODO: in the cache state to see if it is valid
// check whether the data is already cached
std::unique_ptr<CacheData> task = GetFromCache(data, size, dst_node);
if (task != nullptr) { return std::move(task); }
// at this point the requested data is not present in cache
// and we create a caching task for it
task = std::make_unique<CacheData>(data, size);
{ std::unique_lock<std::shared_mutex> lock(cache_mutex_);
const auto state = cache_state_[dst_node].emplace(task->src_, *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 return the other
// threads data cache structure
if (!state.second) { std::cout << "[!] Found another cache instance for 0x" << std::hex << (uint64_t)task->src_ << std::dec << std::endl; return std::move(std::make_unique<CacheData>(state.first->second)); } }
SubmitTask(task.get(), dst_node, src_node);
return std::move(task); }
inline uint8_t* dsacache::Cache::AllocOnNode(const size_t size, const int node) { // 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
// check currently free memory to see if the data fits
long long int free_space = 0; numa_node_size64(node, &free_space);
if (free_space < size) { std::cout << "[!] Memory shortage when allocating " << size << "B on node " << node << std::endl;
// dst node lacks memory space so we flush the cache for this
// node hoping to free enough currently unused entries to make
// the second allocation attempt successful
Flush(node);
// re-test by getting the free space and checking again
numa_node_size64(node, &free_space);
if (free_space < size) { std::cout << "[x] Memory shortage after flush when allocating " << size << "B on node " << node << std::endl;
return nullptr; } }
uint8_t* dst = reinterpret_cast<uint8_t*>(numa_alloc_onnode(size, node));
if (dst == nullptr) { std::cout << "[x] Allocation try failed for " << size << "B on node " << node << std::endl;
return nullptr; }
return dst; }
inline void dsacache::Cache::SubmitTask(CacheData* task, const int dst_node, const int src_node) { uint8_t* dst = AllocOnNode(task->size_, dst_node);
if (dst == nullptr) { std::cout << "[x] Allocation failed so we can not cache" << std::endl; return; }
task->incomplete_cache_ = dst;
// querry copy policy function for the nodes to use for the copy
const std::vector<int> executing_nodes = copy_policy_function_(dst_node, src_node, task->size_); const size_t task_count = executing_nodes.size();
// 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
bitmask* 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->src_ + local_offset; uint8_t* local_dst = dst + local_offset;
task->handlers_->emplace_back(ExecuteCopy(local_src, local_dst, local_size, executing_nodes[i])); }
// restore the previous nodemask
numa_run_on_node_mask(nodemask); numa_free_nodemask(nodemask); }
inline dml::handler<dml::mem_copy_operation, std::allocator<uint8_t>> dsacache::Cache::ExecuteCopy( const uint8_t* src, uint8_t* dst, const size_t size, const int node ) const { dml::const_data_view srcv = dml::make_view(src, size); dml::data_view dstv = dml::make_view(dst, size);
numa_run_on_node(node);
return dml::submit<dml::automatic>(dml::mem_copy.block_on_fault(), srcv, dstv); }
inline void dsacache::Cache::GetCacheNode(uint8_t* src, const size_t size, int* OUT_DST_NODE, int* OUT_SRC_NODE) const { // 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
*OUT_SRC_NODE = -1; get_mempolicy(OUT_SRC_NODE, NULL, 0, (void*)src, MPOL_F_NODE | MPOL_F_ADDR);
// querry cache policy function for the destination numa node
*OUT_DST_NODE = cache_policy_function_(current_node, *OUT_SRC_NODE, size); }
inline void dsacache::Cache::Flush(const int node) { // this lambda is used because below we have two code paths that
// flush nodes, either one single or all successively
const auto FlushNode = [](std::unordered_map<uint8_t*,CacheData>& map) { // begin at the front of the map
auto it = map.begin();
// loop until we reach the end of the map
while (it != map.end()) { // if the iterator points to an inactive element
// then we may erase it
if (it->second.Active() == false) { // erase the iterator from the map
map.erase(it);
// as the erasure invalidated out iterator
// we must start at the beginning again
it = map.begin(); } else { // if element is active just move over to the next one
it++; } } };
{ // we require exclusive lock as we modify the cache state
std::unique_lock<std::shared_mutex> lock(cache_mutex_);
// node == -1 means that cache on all nodes should be flushed
if (node == -1) { for (auto& nc : cache_state_) { FlushNode(nc.second); } } else { FlushNode(cache_state_[node]); } } }
inline std::unique_ptr<dsacache::CacheData> dsacache::Cache::GetFromCache(uint8_t* src, const size_t size, const int dst_node) { // 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
// lock the cache state in shared-mode because we read
std::shared_lock<std::shared_mutex> lock(cache_mutex_);
// search for the data in our cache state structure at the given node
const auto search = cache_state_[dst_node].find(src);
// if the data is in our structure we continue
if (search != cache_state_[dst_node].end()) {
// now check whether the sizes match
if (search->second.size_ >= size) { // return a unique copy of the entry which uses the object
// lifetime and destructor to safely handle deallocation
return std::move(std::make_unique<CacheData>(search->second)); } else { // if the sizes missmatch then we clear the current entry from cache
// which will cause its deletion only after the last possible outside
// reference is also destroyed
cache_state_[dst_node].erase(search); } }
return nullptr; }
void dsacache::Cache::Invalidate(uint8_t* data) { // as the cache is modified we must obtain a unique writers lock
std::unique_lock<std::shared_mutex> lock(cache_mutex_);
// loop through all per-node-caches available
for (auto node : cache_state_) { // search for an entry for the given data pointer
auto search = node.second.find(data);
if (search != node.second.end()) { // if the data is represented in-cache
// then it will be erased to re-trigger
// caching on next access
node.second.erase(search); } } }
inline dsacache::CacheData::CacheData(uint8_t* data, const size_t size) { src_ = data; size_ = size; active_ = new std::atomic<int32_t>(1); cache_ = new std::atomic<uint8_t*>(); incomplete_cache_ = nullptr; handlers_ = std::make_unique<std::vector<dml_handler>>(); }
inline dsacache::CacheData::CacheData(const dsacache::CacheData& other) { // we copy the ptr to the global atomic reference counter
// and increase the amount of active references
active_ = other.active_; const int current_active = active_->fetch_add(1);
// source and size will be copied too
// as well as the reference to the global
// atomic cache pointer
src_ = other.src_; size_ = other.size_; cache_ = other.cache_;
// incomplete cache and handlers will not
// be copied because only the first instance
// will wait on the completion of handlers
incomplete_cache_ = nullptr; handlers_ = nullptr; }
inline dsacache::CacheData::~CacheData() { // if this is the first instance of this cache structure
// and it has not been waited on and is now being destroyed
// we must wait on completion here to ensure the cache
// remains in a valid state
if (handlers_ != nullptr) { WaitOnCompletion(); }
// due to fetch_sub returning the preivously held value
// we must subtract one locally to get the current value
const int32_t v = active_->fetch_sub(1) - 1;
// if the returned value is zero or lower
// then we must execute proper deletion
// as this was the last reference
if (v <= 0) { Deallocate();
delete active_; delete cache_; } }
inline void dsacache::CacheData::Deallocate() { // although deallocate should only be called from
// a safe context to do so, it can not hurt to
// defensively perform the operation atomically
uint8_t* cache_local = cache_->exchange(nullptr); if (cache_local != nullptr) numa_free(cache_local, size_);
// if the cache was never waited for then incomplete_cache_
// may still contain a valid pointer which has to be freed
if (incomplete_cache_ != nullptr) numa_free(incomplete_cache_, size_); }
inline uint8_t* dsacache::CacheData::GetDataLocation() const { return cache_->load(); }
inline bool dsacache::CacheData::Active() const { // this entry is active if more than one
// reference exists to it, as the Cache
// will always keep one internally until
// the entry is cleared from cache
return active_->load() > 1; }
inline void dsacache::CacheData::WaitOnCompletion() { // the cache data entry can be in two states
// either it is the original one which has not
// been waited for in which case the handlers
// are non-null or it is not
if (handlers_ == nullptr) { // when no handlers are attached to this cache entry we wait on a
// value change for the cache structure from nullptr to non-null
// which will either go through immediately if the cache is valid
// already or wait until the handler-owning thread notifies us
cache_->wait(nullptr); } else { // when the handlers are non-null there are some DSA task handlers
// available on which we must wait here
// abort is set if any operation encountered an error
bool abort = false;
for (auto& handler : *handlers_) { auto result = handler.get();
if (result.status != dml::status_code::ok) { std::cerr << "[x] Encountered bad status code for operation: " << dml::StatusCodeToString(result.status) << std::endl;
// if one of the copy tasks failed we abort the whole task
// after all operations are completed on it
abort = true; } }
// the handlers are cleared after all have completed
handlers_ = nullptr;
// now we act depending on whether an abort has been
// called for which signals operation incomplete
if (abort) { // store nullptr in the cache location
cache_->store(nullptr);
// then free the now incomplete cache
// TODO: it would be possible to salvage the
// TODO: operation at this point but this
// TODO: is quite complicated so we just abort
numa_free(incomplete_cache_, size_); } else { // incomplete cache is now safe to use and therefore we
// swap it with the global cache state of this entry
// and notify potentially waiting threads
cache_->store(incomplete_cache_); }
// as a last step all waiting threads must
// be notified (copies of this will wait on value
// change of the cache) and the incomplete cache
// is cleared to nullptr as it is not incomplete
cache_->notify_all(); incomplete_cache_ = nullptr; } }
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