Introduce optimistic fast path for engine_rd

Signed-off-by: Avi Halaf <avi.halaf@huawei.com>
Signed-off-by: Robert Baldyga <robert.baldyga@huawei.com>
Signed-off-by: Michal Mielewczyk <michal.mielewczyk@huawei.com>

src/concurrency/ocf_cache_line_concurrency.c

@@ -33,7 +33,7 @@ static ocf_cache_line_t ocf_cl_lock_line_get_entry(
 	return req->map[index].coll_idx;
 }
 
-static int ocf_cl_lock_line_fast(struct ocf_alock *alock,
+int ocf_cl_lock_line_fast(struct ocf_alock *alock,
 		struct ocf_request *req, int rw)
 {
 	int32_t i;

src/engine/engine_rd.c

@@ -258,3 +258,46 @@ int ocf_read_generic(struct ocf_request *req)
 
 	return 0;
 }
+
+int ocf_read_generic_try_fast(struct ocf_request *req)
+{
+	struct ocf_alock *c = ocf_cache_line_concurrency(req->cache);
+
+	/* Calculate hashes for hash-bucket locking */
+	ocf_req_hash(req);
+
+	/* Read-lock hash buckets associated with request target core & LBAs
+	* (core lines) to assure that cache mapping for these core lines does
+	* not change during traversation */
+	ocf_hb_req_prot_lock_rd(req);
+
+	/* check CL status */
+	ocf_engine_lookup(req);
+
+	if (ocf_engine_is_mapped(req) && ocf_engine_is_hit(req) &&
+			ocf_cl_lock_line_fast(c, req, OCF_READ) == OCF_LOCK_ACQUIRED) {
+
+		OCF_DEBUG_RQ(req, "Submit read generic fast");
+
+		ocf_req_get(req);
+		ocf_engine_set_hot(req);
+		ocf_hb_req_prot_unlock_rd(req);
+
+		if (ocf_engine_needs_repart(req)) {
+			ocf_hb_req_prot_lock_wr(req);
+			ocf_user_part_move(req);
+			ocf_hb_req_prot_unlock_wr(req);
+		}
+
+		ocf_read_generic_submit_hit(req);
+
+		/* Update statistics */
+		ocf_engine_update_request_stats(req);
+		ocf_engine_update_block_stats(req);
+		return OCF_FAST_PATH_YES;
+	} else {
+		ocf_hb_req_prot_unlock_rd(req);
+		OCF_DEBUG_RQ(req, "Failed to read generic fast");
+		return OCF_FAST_PATH_NO;
+	}
+}

src/engine/engine_rd.h

@@ -1,5 +1,6 @@
 /*
  * Copyright(c) 2012-2021 Intel Corporation
+ * Copyright(c) 2024 Huawei Technologies
  * SPDX-License-Identifier: BSD-3-Clause
  */
 
@@ -9,5 +10,6 @@
 int ocf_read_generic(struct ocf_request *req);
 
 void ocf_read_generic_submit_hit(struct ocf_request *req);
+int ocf_read_generic_try_fast(struct ocf_request *req);
 
 #endif /* ENGINE_RD_H_ */

src/ocf_core.c

@@ -10,9 +10,12 @@
 #include "ocf_io_priv.h"
 #include "metadata/metadata.h"
 #include "engine/cache_engine.h"
+#include "engine/engine_rd.h"
 #include "utils/utils_user_part.h"
 #include "ocf_request.h"
 
+#define MAX_FAST_PATH_CACHE_LINES (64)
+
 struct ocf_core_volume {
 	ocf_core_t core;
 };
@@ -218,6 +221,29 @@ static void ocf_req_complete(struct ocf_request *req, int error)
 	ocf_io_put(&req->ioi.io);
 }
 
+static inline int _ocf_core_submit_io_fast_rd_generic(struct ocf_io *io,
+		struct ocf_request *req)
+{
+	int res;
+
+	switch (req->cache_mode) {
+		case ocf_req_cache_mode_wt:
+		case ocf_req_cache_mode_wa:
+		case ocf_req_cache_mode_wi:
+		case ocf_req_cache_mode_wb:
+		case ocf_req_cache_mode_wo:
+			res = ocf_read_generic_try_fast(req);
+			break;
+		default:
+			break;
+	}
+
+	if (res == OCF_FAST_PATH_NO)
+		ocf_req_clear_map(req);
+
+	return res;
+}
+
 static inline ocf_req_cache_mode_t _ocf_core_req_resolve_fast_mode(
 		ocf_cache_t cache, struct ocf_request *req)
 {
@@ -248,6 +274,14 @@ static int ocf_core_submit_io_fast(struct ocf_io *io, struct ocf_request *req,
 	if (req->cache_mode == ocf_req_cache_mode_pt)
 		return OCF_FAST_PATH_NO;
 
+	/* If a read request isn't too big for a lookup in submission context,
+	   check it is a read-hit and if cache line lock could be acquired
+	   without waiting. If so, submit immediately */
+	if (req->rw == OCF_READ) {
+		if (req->core_line_count <= MAX_FAST_PATH_CACHE_LINES)
+			return _ocf_core_submit_io_fast_rd_generic(io, req);
+	}
+
 	resolved_mode = _ocf_core_req_resolve_fast_mode(cache, req);
 	if (resolved_mode == ocf_req_cache_mode_max)
 		return OCF_FAST_PATH_NO;