Advanced request handling optimizations

src/plugins/ucx/ucx_backend.cpp

@@ -265,40 +265,14 @@ void nixlUcxEngine::vramFiniCtx()
     cudaCtx.reset();
 }
 
-/****************************************
- * UCX request management
-*****************************************/
-
-
-class nixlUcxIntReq {
-public:
-    operator nixlUcxReq() noexcept {
-        return static_cast<nixlUcxReq>(this);
-    }
-
-    void
-    setConnection(nixlUcxConnection *conn) {
-        conn_ = conn;
-    }
-
-    nixl_status_t
-    checkConnection(size_t ep_id) const {
-        NIXL_ASSERT(conn_) << "Connection is not set";
-        return conn_->getEp(ep_id)->checkTxState();
-    }
-
-private:
-    nixlUcxConnection *conn_;
-};
-
 /****************************************
  * Backend request management
 *****************************************/
 
 class nixlUcxBackendH : public nixlBackendReqH {
 private:
     std::set<ucx_connection_ptr_t> connections_;
-    std::vector<nixlUcxIntReq *> requests_;
+    std::vector<nixlUcxReq> requests_;
     nixlUcxWorker *worker;
     size_t worker_id;
 
@@ -313,26 +287,54 @@ class nixlUcxBackendH : public nixlBackendReqH {
     };
     std::optional<Notif> notif;
 
-public:
-    auto& notification() {
-        return notif;
+    nixl_status_t
+    checkConnection(nixl_status_t status = NIXL_SUCCESS) const {
+        NIXL_ASSERT(!connections_.empty());
+        for (const auto &conn : connections_) {
+            nixl_status_t conn_status = conn->getEp(worker_id)->checkTxState();
+            if (conn_status != NIXL_SUCCESS) {
+                return conn_status;
+            }
+        }
+        return status;
     }
 
+public:
     nixlUcxBackendH(nixlUcxWorker *worker, size_t worker_id)
         : worker(worker),
           worker_id(worker_id) {}
 
+    auto &
+    notification() {
+        return notif;
+    }
+
     void
     reserve(size_t size) {
         requests_.reserve(size);
     }
 
-    void
-    append(nixlUcxReq req, ucx_connection_ptr_t conn) {
-        auto req_int = static_cast<nixlUcxIntReq *>(req);
-        req_int->setConnection(conn.get());
-        requests_.push_back(req_int);
+    nixl_status_t
+    append(nixl_status_t status, nixlUcxReq req, ucx_connection_ptr_t conn) {
         connections_.insert(conn);
+        switch (status) {
+        case NIXL_IN_PROG:
+            requests_.push_back(req);
+            break;
+        case NIXL_SUCCESS:
+            // Nothing to do
+            break;
+        default:
+            // Error. Release all previously initiated ops and exit:
+            release();
+            return status;
+        }
+        return NIXL_SUCCESS;
+    }
+
+    const std::set<ucx_connection_ptr_t> &
+    getConnections() const {
+        return connections_;
     }
 
     virtual bool
@@ -343,7 +345,7 @@ class nixlUcxBackendH : public nixlBackendReqH {
     virtual nixl_status_t
     release() {
         // TODO: Error log: uncompleted requests found! Cancelling ...
-        for (nixlUcxIntReq *req : requests_) {
+        for (nixlUcxReq req : requests_) {
             nixl_status_t ret = ucx_status_to_nixl(ucp_request_check_status(req));
             if (ret == NIXL_IN_PROG) {
                 // TODO: Need process this properly.
@@ -370,20 +372,19 @@ class nixlUcxBackendH : public nixlBackendReqH {
 
         /* If last request is incomplete, return NIXL_IN_PROG early without
          * checking other requests */
-        nixlUcxIntReq *req = requests_.back();
+        nixlUcxReq req = requests_.back();
         nixl_status_t ret = ucx_status_to_nixl(ucp_request_check_status(req));
         if (ret == NIXL_IN_PROG) {
             return NIXL_IN_PROG;
         } else if (ret != NIXL_SUCCESS) {
-            nixl_status_t conn_status = req->checkConnection(worker_id);
-            return (conn_status == NIXL_SUCCESS) ? ret : conn_status;
+            return checkConnection(ret);
         }
 
         /* Last request completed successfully, all the others must be in the
          * same state. TODO: remove extra checks? */
         size_t incomplete_reqs = 0;
         nixl_status_t out_ret = NIXL_SUCCESS;
-        for (nixlUcxIntReq *req : requests_) {
+        for (nixlUcxReq req : requests_) {
             nixl_status_t ret = ucx_status_to_nixl(ucp_request_check_status(req));
             if (__builtin_expect(ret == NIXL_SUCCESS, 0)) {
                 worker->reqRelease(req);
@@ -394,8 +395,7 @@ class nixlUcxBackendH : public nixlBackendReqH {
                 requests_[incomplete_reqs++] = req;
             } else {
                 // Any other ret value is ERR and will be returned
-                nixl_status_t conn_status = req->checkConnection(worker_id);
-                out_ret = (conn_status == NIXL_SUCCESS) ? ret : conn_status;
+                out_ret = checkConnection(ret);
             }
         }
 
@@ -1102,7 +1102,7 @@ nixlUcxEngine::nixlUcxEngine(const nixlBackendInitParams &init_params)
     }
 
     uc = std::make_unique<nixlUcxContext>(
-        devs, sizeof(nixlUcxIntReq), init_params.enableProgTh, num_workers, init_params.syncMode);
+        devs, init_params.enableProgTh, num_workers, init_params.syncMode);
 
     for (size_t i = 0; i < num_workers; i++) {
         uws.emplace_back(std::make_unique<nixlUcxWorker>(*uc, err_handling_mode));
@@ -1324,24 +1324,6 @@ nixl_status_t nixlUcxEngine::unloadMD (nixlBackendMD* input) {
  * Data movement
 *****************************************/
 
-static nixl_status_t
-_retHelper(nixl_status_t ret, nixlUcxBackendH *hndl, nixlUcxReq &req, ucx_connection_ptr_t conn) {
-    /* if transfer wasn't immediately completed */
-    switch(ret) {
-    case NIXL_IN_PROG:
-        hndl->append(req, conn);
-    case NIXL_SUCCESS:
-        // Nothing to do
-        break;
-    default:
-        // Error. Release all previously initiated ops and exit:
-        hndl->release();
-        return ret;
-    }
-
-    return NIXL_SUCCESS;
-}
-
 size_t
 nixlUcxEngine::getWorkerId() const {
     auto it = tlsSharedWorkerMap().find(this);
@@ -1461,6 +1443,56 @@ nixl_status_t nixlUcxEngine::estimateXferCost (const nixl_xfer_op_t &operation,
     return NIXL_SUCCESS;
 }
 
+nixlUcxEngine::batchResult
+nixlUcxEngine::sendXferRangeBatch(nixlUcxEp &ep,
+                                  nixl_xfer_op_t operation,
+                                  const nixl_meta_dlist_t &local,
+                                  const nixl_meta_dlist_t &remote,
+                                  size_t worker_id,
+                                  size_t start_idx,
+                                  size_t end_idx) {
+    batchResult result = {NIXL_SUCCESS, 0, nullptr};
+
+    for (size_t i = start_idx; i < end_idx; ++i) {
+        void *laddr = (void *)local[i].addr;
+        size_t lsize = local[i].len;
+        uint64_t raddr = (uint64_t)remote[i].addr;
+        NIXL_ASSERT(lsize == remote[i].len);
+
+        auto lmd = static_cast<nixlUcxPrivateMetadata *>(local[i].metadataP);
+        auto rmd = static_cast<nixlUcxPublicMetadata *>(remote[i].metadataP);
+        auto &rmd_ep = rmd->conn->getEp(worker_id);
+        if (__builtin_expect(rmd_ep.get() != &ep, 0)) {
+            break;
+        }
+
+        ++result.size;
+        nixlUcxReq req;
+        nixl_status_t ret = operation == NIXL_READ ?
+            ep.read(raddr, rmd->getRkey(worker_id), laddr, lmd->mem, lsize, req) :
+            ep.write(laddr, lmd->mem, raddr, rmd->getRkey(worker_id), lsize, req);
+
+        if (ret == NIXL_IN_PROG) {
+            if (__builtin_expect(result.req != nullptr, 1)) {
+                ucp_request_free(result.req);
+            }
+            result.req = req;
+        } else if (ret != NIXL_SUCCESS) {
+            result.status = ret;
+            if (result.req != nullptr) {
+                ucp_request_free(result.req);
+                result.req = nullptr;
+            }
+            break;
+        }
+    }
+
+    if (result.status == NIXL_SUCCESS && result.req) {
+        result.status = NIXL_IN_PROG;
+    }
+    return result;
+}
+
 nixl_status_t
 nixlUcxEngine::sendXferRange(const nixl_xfer_op_t &operation,
                              const nixl_meta_dlist_t &local,
@@ -1470,54 +1502,44 @@ nixlUcxEngine::sendXferRange(const nixl_xfer_op_t &operation,
                              size_t start_idx,
                              size_t end_idx) const {
     nixlUcxBackendH *intHandle = (nixlUcxBackendH *)handle;
-    nixlUcxPrivateMetadata *lmd;
-    nixlUcxPublicMetadata *rmd;
-    nixl_status_t ret;
-    nixlUcxReq req;
     size_t workerId = intHandle->getWorkerId();
+    nixl_status_t ret;
 
-    // Reserve space for the requests, +2 for flush and completion
-    intHandle->reserve(end_idx - start_idx + 2);
+    if (operation != NIXL_WRITE && operation != NIXL_READ) {
+        return NIXL_ERR_INVALID_PARAM;
+    }
 
-    for (size_t i = start_idx; i < end_idx; i++) {
-        void *laddr = (void*) local[i].addr;
-        size_t lsize = local[i].len;
-        uint64_t raddr = (uint64_t)remote[i].addr;
-        size_t rsize = remote[i].len;
+    /* Assuming we have a single EP, we need 3 requests: one pending request,
+     * one flush request, and one notification request */
+    intHandle->reserve(3);
 
-        lmd = (nixlUcxPrivateMetadata*) local[i].metadataP;
-        rmd = (nixlUcxPublicMetadata*) remote[i].metadataP;
+    for (size_t i = start_idx; i < end_idx;) {
+        /* Send requests to a single EP */
+        auto rmd = static_cast<nixlUcxPublicMetadata *>(remote[i].metadataP);
         auto &ep = rmd->conn->getEp(workerId);
+        auto result = sendXferRangeBatch(*ep, operation, local, remote, workerId, i, end_idx);
 
-        if (lsize != rsize) {
-            return NIXL_ERR_INVALID_PARAM;
-        }
-
-        switch (operation) {
-        case NIXL_READ:
-            ret = ep->read(raddr, rmd->getRkey(workerId), laddr, lmd->mem, lsize, req);
-            break;
-        case NIXL_WRITE:
-            ret = ep->write(laddr, lmd->mem, raddr, rmd->getRkey(workerId), lsize, req);
-            break;
-        default:
-            return NIXL_ERR_INVALID_PARAM;
-        }
-
-        if (_retHelper(ret, intHandle, req, rmd->conn)) {
+        /* Append a single pending request for the entire EP batch */
+        ret = intHandle->append(result.status, result.req, rmd->conn);
+        if (ret != NIXL_SUCCESS) {
             return ret;
         }
+
+        i += result.size;
     }
 
     /*
      * Flush keeps intHandle non-empty until the operation is actually
      * completed, which can happen after local requests completion.
+     * We need to flush all distinct connections to ensure that the operation
+     * is actually completed.
      */
-    rmd = (nixlUcxPublicMetadata *)remote[0].metadataP;
-    ret = rmd->conn->getEp(workerId)->flushEp(req);
-
-    if (_retHelper(ret, intHandle, req, rmd->conn)) {
-        return ret;
+    for (auto &conn : intHandle->getConnections()) {
+        nixlUcxReq req;
+        ret = conn->getEp(workerId)->flushEp(req);
+        if (intHandle->append(ret, req, conn) != NIXL_SUCCESS) {
+            return ret;
+        }
     }
 
     return NIXL_SUCCESS;
@@ -1557,7 +1579,7 @@ nixlUcxEngine::postXfer(const nixl_xfer_op_t &operation,
                                 opt_args->notifMsg,
                                 rmd->conn->getEp(int_handle->getWorkerId()),
                                 &req);
-            if (_retHelper(ret, int_handle, req, rmd->conn)) {
+            if (int_handle->append(ret, req, rmd->conn) != NIXL_SUCCESS) {
                 return ret;
             }
 
@@ -1594,8 +1616,8 @@ nixl_status_t nixlUcxEngine::checkXfer (nixlBackendReqH* handle) const
     nixl_status_t status =
         notifSendPriv(notif->agent, notif->payload, conn->getEp(intHandle->getWorkerId()), &req);
     notif.reset();
-    status = _retHelper(status, intHandle, req, conn);
-    if (status != NIXL_SUCCESS) {
+
+    if (intHandle->append(status, req, conn) != NIXL_SUCCESS) {
         return status;
     }
 

src/plugins/ucx/ucx_backend.h

@@ -294,6 +294,21 @@ class nixlUcxEngine : public nixlBackendEngine {
     ucx_connection_ptr_t
     getConnection(const std::string &remote_agent) const;
 
+    struct batchResult {
+        nixl_status_t status;
+        size_t size;
+        nixlUcxReq req;
+    };
+
+    static batchResult
+    sendXferRangeBatch(nixlUcxEp &ep,
+                       nixl_xfer_op_t operation,
+                       const nixl_meta_dlist_t &local,
+                       const nixl_meta_dlist_t &remote,
+                       size_t worker_id,
+                       size_t start_idx,
+                       size_t end_idx);
+
     /* UCX data */
     std::unique_ptr<nixlUcxContext> uc;
     std::vector<std::unique_ptr<nixlUcxWorker>> uws;

src/utils/ucx/ucx_utils.cpp

@@ -406,7 +406,6 @@ bool nixlUcxMtLevelIsSupported(const nixl_ucx_mt_t mt_type) noexcept
 }
 
 nixlUcxContext::nixlUcxContext(std::vector<std::string> devs,
-                               size_t req_size,
                                bool prog_thread,
                                unsigned long num_workers,
                                nixl_thread_sync_t sync_mode) {
@@ -429,11 +428,6 @@ nixlUcxContext::nixlUcxContext(std::vector<std::string> devs,
         ucp_params.features |= UCP_FEATURE_WAKEUP;
     ucp_params.mt_workers_shared = num_workers > 1 ? 1 : 0;
 
-    if (req_size) {
-        ucp_params.request_size = req_size;
-        ucp_params.field_mask |= UCP_PARAM_FIELD_REQUEST_SIZE;
-    }
-
     nixl::ucx::config config;
 
     /* If requested, restrict the set of network devices */

src/utils/ucx/ucx_utils.h

@@ -199,7 +199,6 @@ class nixlUcxContext {
 
 public:
     nixlUcxContext(std::vector<std::string> devices,
-                   size_t req_size,
                    bool prog_thread,
                    unsigned long num_workers,
                    nixl_thread_sync_t sync_mode);