[PATCH v10 1/7] eal: add static per-lcore memory allocation facility

["Mattias Rönnblom" <mattias.ronnblom@ericsson.com>]

Introduce DPDK per-lcore id variables, or lcore variables for short.

An lcore variable has one value for every current and future lcore
id-equipped thread.

The primary <rte_lcore_var.h> use case is for statically allocating
small, frequently-accessed data structures, for which one instance
should exist for each lcore.

Lcore variables are similar to thread-local storage (TLS, e.g., C11
_Thread_local), but decoupling the values' life time with that of the
threads.

Lcore variables are also similar in terms of functionality provided by
FreeBSD kernel's DPCPU_*() family of macros and the associated
build-time machinery. DPCPU uses linker scripts, which effectively
prevents the reuse of its, otherwise seemingly viable, approach.

The currently-prevailing way to solve the same problem as lcore
variables is to keep a module's per-lcore data as RTE_MAX_LCORE-sized
array of cache-aligned, RTE_CACHE_GUARDed structs. The benefit of
lcore variables over this approach is that data related to the same
lcore now is close (spatially, in memory), rather than data used by
the same module, which in turn avoid excessive use of padding,
polluting caches with unused data.

Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
Acked-by: Morten Brørup <mb@smartsharesystems.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@huawei.com>
Acked-by: Chengwen Feng <fengchengwen@huawei.com>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>

--

PATCH v10:
 * Improve documentation grammar and spelling. (Stephen Hemminger,
   Thomas Monjalon)
 * Add version.map DPDK version comment. (Thomas Monjalon)

PATCH v9:
 * Fixed merge conflicts in release notes.

PATCH v8:
 * Work around missing max_align_t definition in MSVC. (Morten Brørup)

PATCH v7:
 * Add () to the FOREACH lcore id macro parameter, to allow arbitrary
   expression, not just a simple variable name, being passed.
   (Konstantin Ananyev)

PATCH v6:
 * Have API user provide the loop variable in the FOREACH macro, to
   avoid subtle bugs where the loop variable name clashes with some
   other user-defined variable. (Konstantin Ananyev)

PATCH v5:
 * Update EAL programming guide.

PATCH v2:
 * Add Windows support. (Morten Brørup)
 * Fix lcore variables API index reference. (Morten Brørup)
 * Various improvements of the API documentation. (Morten Brørup)
 * Elimination of unused symbol in version.map. (Morten Brørup)

PATCH:
 * Update MAINTAINERS and release notes.
 * Stop covering included files in extern "C" {}.

RFC v6:
 * Include <stdlib.h> to get aligned_alloc().
 * Tweak documentation (grammar).
 * Provide API-level guarantees that lcore variable values take on an
   initial value of zero.
 * Fix misplaced __rte_cache_aligned in the API doc example.

RFC v5:
 * In Doxygen, consistenly use @<cmd> (and not \<cmd>).
 * The RTE_LCORE_VAR_GET() and SET() convience access macros
   covered an uncommon use case, where the lcore value is of a
   primitive type, rather than a struct, and is thus eliminated
   from the API. (Morten Brørup)
 * In the wake up GET()/SET() removeal, rename RTE_LCORE_VAR_PTR()
   RTE_LCORE_VAR_VALUE().
 * The underscores are removed from __rte_lcore_var_lcore_ptr() to
   signal that this function is a part of the public API.
 * Macro arguments are documented.

RFV v4:
 * Replace large static array with libc heap-allocated memory. One
   implication of this change is there no longer exists a fixed upper
   bound for the total amount of memory used by lcore variables.
   RTE_MAX_LCORE_VAR has changed meaning, and now represent the
   maximum size of any individual lcore variable value.
 * Fix issues in example. (Morten Brørup)
 * Improve access macro type checking. (Morten Brørup)
 * Refer to the lcore variable handle as "handle" and not "name" in
   various macros.
 * Document lack of thread safety in rte_lcore_var_alloc().
 * Provide API-level assurance the lcore variable handle is
   always non-NULL, to all applications to use NULL to mean
   "not yet allocated".
 * Note zero-sized allocations are not allowed.
 * Give API-level guarantee the lcore variable values are zeroed.

RFC v3:
 * Replace use of GCC-specific alignof(<expression>) with alignof(<type>).
 * Update example to reflect FOREACH macro name change (in RFC v2).

RFC v2:
 * Use alignof to derive alignment requirements. (Morten Brørup)
 * Change name of FOREACH to make it distinct from <rte_lcore.h>'s
   *per-EAL-thread* RTE_LCORE_FOREACH(). (Morten Brørup)
 * Allow user-specified alignment, but limit max to cache line size.
---
 MAINTAINERS                                   |   6 +
 config/rte_config.h                           |   1 +
 doc/api/doxy-api-index.md                     |   1 +
 .../prog_guide/env_abstraction_layer.rst      |  43 +-
 doc/guides/rel_notes/release_24_11.rst        |  14 +
 lib/eal/common/eal_common_lcore_var.c         |  85 ++++
 lib/eal/common/meson.build                    |   1 +
 lib/eal/include/meson.build                   |   1 +
 lib/eal/include/rte_lcore_var.h               | 389 ++++++++++++++++++
 lib/eal/version.map                           |   3 +
 10 files changed, 538 insertions(+), 6 deletions(-)
 create mode 100644 lib/eal/common/eal_common_lcore_var.c
 create mode 100644 lib/eal/include/rte_lcore_var.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 812463fe9f..61e5907fb5 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -282,6 +282,12 @@ F: lib/eal/include/rte_random.h
 F: lib/eal/common/rte_random.c
 F: app/test/test_rand_perf.c
 
+Lcore Variables
+M: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
+F: lib/eal/include/rte_lcore_var.h
+F: lib/eal/common/eal_common_lcore_var.c
+F: app/test/test_lcore_var.c
+
 ARM v7
 M: Wathsala Vithanage <wathsala.vithanage@arm.com>
 F: config/arm/
diff --git a/config/rte_config.h b/config/rte_config.h
index fd6f8a2f1a..498d509244 100644
--- a/config/rte_config.h
+++ b/config/rte_config.h
@@ -41,6 +41,7 @@
 /* EAL defines */
 #define RTE_CACHE_GUARD_LINES 1
 #define RTE_MAX_HEAPS 32
+#define RTE_MAX_LCORE_VAR 1048576
 #define RTE_MAX_MEMSEG_LISTS 128
 #define RTE_MAX_MEMSEG_PER_LIST 8192
 #define RTE_MAX_MEM_MB_PER_LIST 32768
diff --git a/doc/api/doxy-api-index.md b/doc/api/doxy-api-index.md
index f9f0300126..ed577f14ee 100644
--- a/doc/api/doxy-api-index.md
+++ b/doc/api/doxy-api-index.md
@@ -99,6 +99,7 @@ The public API headers are grouped by topics:
   [interrupts](@ref rte_interrupts.h),
   [launch](@ref rte_launch.h),
   [lcore](@ref rte_lcore.h),
+  [lcore variables](@ref rte_lcore_var.h),
   [per-lcore](@ref rte_per_lcore.h),
   [service cores](@ref rte_service.h),
   [keepalive](@ref rte_keepalive.h),
diff --git a/doc/guides/prog_guide/env_abstraction_layer.rst b/doc/guides/prog_guide/env_abstraction_layer.rst
index b9fac1839d..b659a1d085 100644
--- a/doc/guides/prog_guide/env_abstraction_layer.rst
+++ b/doc/guides/prog_guide/env_abstraction_layer.rst
@@ -429,12 +429,43 @@ with them once they're registered.
 Per-lcore and Shared Variables
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-.. note::
-
-    lcore refers to a logical execution unit of the processor, sometimes called a hardware *thread*.
-
-Shared variables are the default behavior.
-Per-lcore variables are implemented using *Thread Local Storage* (TLS) to provide per-thread local storage.
+By default, static variables, memory blocks allocated on the DPDK
+heap, and other types of memory are shared by all DPDK threads.
+
+An application, a DPDK library, or a PMD may opt to keep per-thread state.
+
+Per-thread data can be maintained using either *lcore variables* (see
+``rte_lcore_var.h``), *thread-local storage (TLS)* (see
+``rte_per_lcore.h``), or a static array of ``RTE_MAX_LCORE`` elements,
+indexed by ``rte_lcore_id()``. These methods allow per-lcore data to be
+largely internal to the module and not directly exposed in its
+API. Another approach is to explicitly handle per-thread aspects in
+the API (e.g., the ports in the Eventdev API).
+
+Lcore variables are suitable for small objects that are statically
+allocated at the time of module or application initialization. An
+lcore variable takes on one value for each lcore ID-equipped thread
+(i.e., for both EAL threads and registered non-EAL threads, in total
+``RTE_MAX_LCORE`` instances). The lifetime of lcore variables is
+independent of the owning threads and can, therefore, be initialized
+before the threads are created.
+
+Variables with thread-local storage are allocated when the thread is
+created and exist until the thread terminates. These are applicable
+for every thread in the process. Only very small objects should be
+allocated in TLS, as large TLS objects can significantly slow down
+thread creation and may unnecessarily increase the memory footprint of
+applications that extensively use unregistered threads.
+
+A common but now largely obsolete DPDK pattern is to use a static
+array sized according to the maximum number of lcore ID-equipped
+threads (i.e., with ``RTE_MAX_LCORE`` elements). To avoid *false
+sharing*, each element must be both cache-aligned and include an
+``RTE_CACHE_GUARD``. This extensive use of padding causes internal
+fragmentation (i.e., unused space) and reduces cache hit rates.
+
+For more discussions on per-lcore state, refer to the
+``rte_lcore_var.h`` API documentation.
 
 Logs
 ~~~~
diff --git a/doc/guides/rel_notes/release_24_11.rst b/doc/guides/rel_notes/release_24_11.rst
index 915065a6f9..0e15767d41 100644
--- a/doc/guides/rel_notes/release_24_11.rst
+++ b/doc/guides/rel_notes/release_24_11.rst
@@ -113,6 +113,20 @@ New Features
 
   * Added independent enqueue feature.
 
+* **Added EAL per-lcore static memory allocation facility.**
+
+    Added EAL API <rte_lcore_var.h> for statically allocating small,
+    frequently-accessed data structures, for which one instance should
+    exist for each EAL thread and registered non-EAL thread.
+
+    With lcore variables, data is organized spatially on a per-lcore id
+    basis, rather than per library or PMD, avoiding the need for cache
+    aligning (or RTE_CACHE_GUARDing) data structures, which in turn
+    reduces CPU cache internal fragmentation, improving performance.
+
+    Lcore variables are similar to thread-local storage (TLS, e.g.,
+    C11 _Thread_local), but decoupling the values' life time from that
+    of the threads.
 
 Removed Items
 -------------
diff --git a/lib/eal/common/eal_common_lcore_var.c b/lib/eal/common/eal_common_lcore_var.c
new file mode 100644
index 0000000000..fac6ab52b0
--- /dev/null
+++ b/lib/eal/common/eal_common_lcore_var.c
@@ -0,0 +1,85 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2024 Ericsson AB
+ */
+
+#include <inttypes.h>
+#include <stdlib.h>
+
+#ifdef RTE_EXEC_ENV_WINDOWS
+#include <malloc.h>
+#endif
+
+#include <rte_common.h>
+#include <rte_debug.h>
+#include <rte_log.h>
+
+#include <rte_lcore_var.h>
+
+#include "eal_private.h"
+
+#define LCORE_BUFFER_SIZE (RTE_MAX_LCORE_VAR * RTE_MAX_LCORE)
+
+static void *lcore_buffer;
+/* initialized to trigger buffer allocation on first lcore_var_alloc() call */
+static size_t offset = RTE_MAX_LCORE_VAR;
+
+static void *
+lcore_var_alloc(size_t size, size_t align)
+{
+	void *handle;
+	unsigned int lcore_id;
+	void *value;
+
+	offset = RTE_ALIGN_CEIL(offset, align);
+
+	if (offset + size > RTE_MAX_LCORE_VAR) {
+#ifdef RTE_EXEC_ENV_WINDOWS
+		lcore_buffer = _aligned_malloc(LCORE_BUFFER_SIZE,
+					       RTE_CACHE_LINE_SIZE);
+#else
+		lcore_buffer = aligned_alloc(RTE_CACHE_LINE_SIZE,
+					     LCORE_BUFFER_SIZE);
+#endif
+		RTE_VERIFY(lcore_buffer != NULL);
+
+		offset = 0;
+	}
+
+	handle = RTE_PTR_ADD(lcore_buffer, offset);
+
+	offset += size;
+
+	RTE_LCORE_VAR_FOREACH_VALUE(lcore_id, value, handle)
+		memset(value, 0, size);
+
+	EAL_LOG(DEBUG, "Allocated %"PRIuPTR" bytes of per-lcore data with a "
+		"%"PRIuPTR"-byte alignment", size, align);
+
+	return handle;
+}
+
+void *
+rte_lcore_var_alloc(size_t size, size_t align)
+{
+	/* Having the per-lcore buffer size aligned on cache lines
+	 * assures as well as having the base pointer aligned on cache
+	 * size assures that aligned offsets also translate to alipgned
+	 * pointers across all values.
+	 */
+	RTE_BUILD_BUG_ON(RTE_MAX_LCORE_VAR % RTE_CACHE_LINE_SIZE != 0);
+	RTE_ASSERT(align <= RTE_CACHE_LINE_SIZE);
+	RTE_ASSERT(size <= RTE_MAX_LCORE_VAR);
+
+	/* '0' means asking for worst-case alignment requirements */
+	if (align == 0)
+#ifdef RTE_TOOLCHAIN_MSVC
+		/* MSVC <stddef.h> is missing the max_align_t typedef */
+		align = alignof(double);
+#else
+		align = alignof(max_align_t);
+#endif
+
+	RTE_ASSERT(rte_is_power_of_2(align));
+
+	return lcore_var_alloc(size, align);
+}
diff --git a/lib/eal/common/meson.build b/lib/eal/common/meson.build
index 22a626ba6f..d41403680b 100644
--- a/lib/eal/common/meson.build
+++ b/lib/eal/common/meson.build
@@ -18,6 +18,7 @@ sources += files(
         'eal_common_interrupts.c',
         'eal_common_launch.c',
         'eal_common_lcore.c',
+        'eal_common_lcore_var.c',
         'eal_common_mcfg.c',
         'eal_common_memalloc.c',
         'eal_common_memory.c',
diff --git a/lib/eal/include/meson.build b/lib/eal/include/meson.build
index e94b056d46..9449253e23 100644
--- a/lib/eal/include/meson.build
+++ b/lib/eal/include/meson.build
@@ -27,6 +27,7 @@ headers += files(
         'rte_keepalive.h',
         'rte_launch.h',
         'rte_lcore.h',
+        'rte_lcore_var.h',
         'rte_lock_annotations.h',
         'rte_malloc.h',
         'rte_mcslock.h',
diff --git a/lib/eal/include/rte_lcore_var.h b/lib/eal/include/rte_lcore_var.h
new file mode 100644
index 0000000000..2f4d388732
--- /dev/null
+++ b/lib/eal/include/rte_lcore_var.h
@@ -0,0 +1,389 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2024 Ericsson AB
+ */
+
+#ifndef _RTE_LCORE_VAR_H_
+#define _RTE_LCORE_VAR_H_
+
+/**
+ * @file
+ *
+ * Lcore variables
+ *
+ * This API provides a mechanism to create and access per-lcore id
+ * variables in a space- and cycle-efficient manner.
+ *
+ * A per-lcore id variable (or lcore variable for short) holds a
+ * unique value for each EAL thread and registered non-EAL
+ * thread. There is one instance for each current and future lcore
+ * id-equipped thread, with a total of @c RTE_MAX_LCORE instances. The
+ * value of the lcore variable for one lcore id is independent from
+ * the values assigned to other lcore ids within the same variable.
+ *
+ * In order to access the values of an lcore variable, a handle is
+ * used. The type of the handle is a pointer to the value's type
+ * (e.g., for an @c uint32_t lcore variable, the handle is a
+ * <code>uint32_t *</code>). The handle type is used to inform the
+ * access macros of the type of the values. A handle may be passed
+ * between modules and threads just like any pointer, but its value
+ * must be treated as an opaque identifier. An allocated handle never
+ * has the value NULL.
+ *
+ * @b Creation
+ *
+ * An lcore variable is created in two steps:
+ *  1. Define an lcore variable handle by using @ref RTE_LCORE_VAR_HANDLE.
+ *  2. Allocate lcore variable storage and initialize the handle with
+ *     a unique identifier by @ref RTE_LCORE_VAR_ALLOC or
+ *     @ref RTE_LCORE_VAR_INIT. Allocation generally occurs at the time
+ *     of module initialization, but may be done at any time.
+ *
+ * The lifetime of an lcore variable is not tied to the thread that
+ * created it. Its per lcore id values (up to @c RTE_MAX_LCORE) are
+ * available from the moment the lcore variable is created and
+ * continue to exist throughout the entire lifetime of the EAL,
+ * whether or not the lcore id is currently in use.
+ *
+ * Lcore variables cannot and need not be freed.
+ *
+ * @b Access
+ *
+ * The value of any lcore variable for any lcore id may be accessed
+ * from any thread (including unregistered threads), but it should
+ * only be *frequently* read from or written to by the owner.
+ *
+ * Values of the same lcore variable, associated with different lcore
+ * ids may be frequently read or written by their respective owners
+ * without risking false sharing.
+ *
+ * An appropriate synchronization mechanism (e.g., atomic loads and
+ * stores) should be employed to prevent data races between the owning
+ * thread and any other thread accessing the same value instance.
+ *
+ * The value of the lcore variable for a particular lcore id is
+ * accessed using @ref RTE_LCORE_VAR_LCORE_VALUE.
+ *
+ * A common pattern is for an EAL thread or a registered non-EAL
+ * thread to access its own lcore variable value. For this purpose, a
+ * shorthand exists as @ref RTE_LCORE_VAR_VALUE.
+ *
+ * Although the handle (as defined by @ref RTE_LCORE_VAR_HANDLE) is a
+ * pointer with the same type as the value, it may not be directly
+ * dereferenced and must be treated as an opaque identifier.
+ *
+ * Lcore variable handles and value pointers may be freely passed
+ * between different threads.
+ *
+ * @b Storage
+ *
+ * An lcore variable's values may be of a primitive type like @c int,
+ * but would more typically be a @c struct.
+ *
+ * The lcore variable handle introduces a per-variable (not
+ * per-value/per-lcore id) overhead of @c sizeof(void *) bytes, so
+ * there are some memory footprint gains to be made by organizing all
+ * per-lcore id data for a particular module as one lcore variable
+ * (e.g., as a struct).
+ *
+ * An application may define an lcore variable handle without ever
+ * allocating it.
+ *
+ * The size of an lcore variable's value must be less than the DPDK
+ * build-time constant @c RTE_MAX_LCORE_VAR.
+ *
+ * Lcore variables are stored in a series of lcore buffers, which are
+ * allocated from the libc heap. Heap allocation failures are treated
+ * as fatal.
+ *
+ * Lcore variables should generally *not* be @ref __rte_cache_aligned
+ * and need *not* include a @ref RTE_CACHE_GUARD field, since the use
+ * of these constructs are designed to avoid false sharing. In the
+ * case of an lcore variable instance, the thread most recently
+ * accessing nearby data structures should almost-always be the lcore
+ * variable's owner. Adding padding will increase the effective memory
+ * working set size, potentially reducing performance.
+ *
+ * Lcore variable values are initialized to zero by default.
+ *
+ * @b Example
+ *
+ * Below is an example of the use of an lcore variable:
+ *
+ * @code{.c}
+ * struct foo_lcore_state {
+ *         int a;
+ *         long b;
+ * };
+ *
+ * static RTE_LCORE_VAR_HANDLE(struct foo_lcore_state, lcore_states);
+ *
+ * long foo_get_a_plus_b(void)
+ * {
+ *         struct foo_lcore_state *state = RTE_LCORE_VAR_VALUE(lcore_states);
+ *
+ *         return state->a + state->b;
+ * }
+ *
+ * RTE_INIT(rte_foo_init)
+ * {
+ *         RTE_LCORE_VAR_ALLOC(lcore_states);
+ *
+ *         unsigned int lcore_id;
+ *         struct foo_lcore_state *state;
+ *         RTE_LCORE_VAR_FOREACH_VALUE(lcore_id, state, lcore_states) {
+ *                 (initialize 'state')
+ *         }
+ *
+ *         (other initialization)
+ * }
+ * @endcode
+ *
+ *
+ * @b Alternatives
+ *
+ * Lcore variables are designed to replace a pattern exemplified below:
+ * @code{.c}
+ * struct __rte_cache_aligned foo_lcore_state {
+ *         int a;
+ *         long b;
+ *         RTE_CACHE_GUARD;
+ * };
+ *
+ * static struct foo_lcore_state lcore_states[RTE_MAX_LCORE];
+ * @endcode
+ *
+ * This scheme is simple and effective, but has one drawback: the data
+ * is organized so that objects related to all lcores for a particular
+ * module are kept close in memory. At a bare minimum, this requires
+ * sizing data structures (e.g., using `__rte_cache_aligned`) to an
+ * even number of cache lines to avoid false sharing. With CPU
+ * hardware prefetching and memory loads resulting from speculative
+ * execution (functions which seemingly are getting more eager faster
+ * than they are getting more intelligent), one or more "guard" cache
+ * lines may be required to separate one lcore's data from another's
+ * and prevent false sharing.
+ *
+ * Lcore variables offer the advantage of working with, rather than
+ * against, the CPU's assumptions. A next-line hardware prefetcher,
+ * for example, may function as intended (i.e., to the benefit, not
+ * detriment, of system performance).
+ *
+ * Another alternative to @ref rte_lcore_var.h is the @ref
+ * rte_per_lcore.h API, which makes use of thread-local storage (TLS,
+ * e.g., GCC __thread or C11 _Thread_local). The main differences
+ * between by using the various forms of TLS (e.g., @ref
+ * RTE_DEFINE_PER_LCORE or _Thread_local) and the use of lcore
+ * variables are:
+ *
+ *   * The lifecycle of a thread-local variable instance is tied to
+ *     that of the thread. The data cannot be accessed before the
+ *     thread has been created, nor after it has exited. As a result,
+ *     thread-local variables must be initialized in a "lazy" manner
+ *     (e.g., at the point of thread creation). Lcore variables may be
+ *     accessed immediately after having been allocated (which may occur
+ *     before any thread beyond the main thread is running).
+ *   * A thread-local variable is duplicated across all threads in the
+ *     process, including unregistered non-EAL threads (i.e.,
+ *     "regular" threads). For DPDK applications heavily relying on
+ *     multi-threading (in conjunction to DPDK's "one thread per core"
+ *     pattern), either by having many concurrent threads or
+ *     creating/destroying threads at a high rate, an excessive use of
+ *     thread-local variables may cause inefficiencies (e.g.,
+ *     increased thread creation overhead due to thread-local storage
+ *     initialization or increased total RAM footprint usage). Lcore
+ *     variables *only* exist for threads with an lcore id.
+ *   * If data in thread-local storage may be shared between threads
+ *     (i.e., can a pointer to a thread-local variable be passed to
+ *     and successfully dereferenced by non-owning thread) depends on
+ *     the specifics of the TLS implementation. With GCC __thread and
+ *     GCC _Thread_local, data sharing between threads is supported.
+ *     In the C11 standard, accessing another thread's _Thread_local
+ *     object is implementation-defined. Lcore variable instances may
+ *     be accessed reliably by any thread.
+ */
+
+#include <stddef.h>
+#include <stdalign.h>
+
+#include <rte_common.h>
+#include <rte_config.h>
+#include <rte_lcore.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * Given the lcore variable type, produces the type of the lcore
+ * variable handle.
+ */
+#define RTE_LCORE_VAR_HANDLE_TYPE(type)		\
+	type *
+
+/**
+ * Define an lcore variable handle.
+ *
+ * This macro defines a variable which is used as a handle to access
+ * the various instances of a per-lcore id variable.
+ *
+ * This macro clarifies that the declaration is an lcore handle, not a
+ * regular pointer.
+ *
+ * Add @b static as a prefix in case the lcore variable is only to be
+ * accessed from a particular translation unit.
+ */
+#define RTE_LCORE_VAR_HANDLE(type, name)	\
+	RTE_LCORE_VAR_HANDLE_TYPE(type) name
+
+/**
+ * Allocate space for an lcore variable, and initialize its handle.
+ *
+ * The values of the lcore variable are initialized to zero.
+ */
+#define RTE_LCORE_VAR_ALLOC_SIZE_ALIGN(handle, size, align)	\
+	handle = rte_lcore_var_alloc(size, align)
+
+/**
+ * Allocate space for an lcore variable, and initialize its handle,
+ * with values aligned for any type of object.
+ *
+ * The values of the lcore variable are initialized to zero.
+ */
+#define RTE_LCORE_VAR_ALLOC_SIZE(handle, size)	\
+	RTE_LCORE_VAR_ALLOC_SIZE_ALIGN(handle, size, 0)
+
+/**
+ * Allocate space for an lcore variable of the size and alignment requirements
+ * suggested by the handle pointer type, and initialize its handle.
+ *
+ * The values of the lcore variable are initialized to zero.
+ */
+#define RTE_LCORE_VAR_ALLOC(handle)					\
+	RTE_LCORE_VAR_ALLOC_SIZE_ALIGN(handle, sizeof(*(handle)),	\
+				       alignof(typeof(*(handle))))
+
+/**
+ * Allocate an explicitly-sized, explicitly-aligned lcore variable by
+ * means of a @ref RTE_INIT constructor.
+ *
+ * The values of the lcore variable are initialized to zero.
+ */
+#define RTE_LCORE_VAR_INIT_SIZE_ALIGN(name, size, align)		\
+	RTE_INIT(rte_lcore_var_init_ ## name)				\
+	{								\
+		RTE_LCORE_VAR_ALLOC_SIZE_ALIGN(name, size, align);	\
+	}
+
+/**
+ * Allocate an explicitly-sized lcore variable by means of a @ref
+ * RTE_INIT constructor.
+ *
+ * The values of the lcore variable are initialized to zero.
+ */
+#define RTE_LCORE_VAR_INIT_SIZE(name, size)		\
+	RTE_LCORE_VAR_INIT_SIZE_ALIGN(name, size, 0)
+
+/**
+ * Allocate an lcore variable by means of a @ref RTE_INIT constructor.
+ *
+ * The values of the lcore variable are initialized to zero.
+ */
+#define RTE_LCORE_VAR_INIT(name)					\
+	RTE_INIT(rte_lcore_var_init_ ## name)				\
+	{								\
+		RTE_LCORE_VAR_ALLOC(name);				\
+	}
+
+/**
+ * Get void pointer to lcore variable instance with the specified
+ * lcore id.
+ *
+ * @param lcore_id
+ *   The lcore id specifying which of the @c RTE_MAX_LCORE value
+ *   instances should be accessed. The lcore id need not be valid
+ *   (e.g., may be @ref LCORE_ID_ANY), but in such a case, the pointer
+ *   is also not valid (and thus should not be dereferenced).
+ * @param handle
+ *   The lcore variable handle.
+ */
+static inline void *
+rte_lcore_var_lcore_ptr(unsigned int lcore_id, void *handle)
+{
+	return RTE_PTR_ADD(handle, lcore_id * RTE_MAX_LCORE_VAR);
+}
+
+/**
+ * Get pointer to lcore variable instance with the specified lcore id.
+ *
+ * @param lcore_id
+ *   The lcore id specifying which of the @c RTE_MAX_LCORE value
+ *   instances should be accessed. The lcore id need not be valid
+ *   (e.g., may be @ref LCORE_ID_ANY), but in such a case, the pointer
+ *   is also not valid (and thus should not be dereferenced).
+ * @param handle
+ *   The lcore variable handle.
+ */
+#define RTE_LCORE_VAR_LCORE_VALUE(lcore_id, handle)			\
+	((typeof(handle))rte_lcore_var_lcore_ptr(lcore_id, handle))
+
+/**
+ * Get pointer to lcore variable instance of the current thread.
+ *
+ * May only be used by EAL threads and registered non-EAL threads.
+ */
+#define RTE_LCORE_VAR_VALUE(handle) \
+	RTE_LCORE_VAR_LCORE_VALUE(rte_lcore_id(), handle)
+
+/**
+ * Iterate over each lcore id's value for an lcore variable.
+ *
+ * @param lcore_id
+ *   An <code>unsigned int</code> variable successively set to the
+ *   lcore id of every valid lcore id (up to @c RTE_MAX_LCORE).
+ * @param value
+ *   A pointer variable successively set to point to lcore variable
+ *   value instance of the current lcore id being processed.
+ * @param handle
+ *   The lcore variable handle.
+ */
+#define RTE_LCORE_VAR_FOREACH_VALUE(lcore_id, value, handle)		\
+	for ((lcore_id) =						\
+		     (((value) = RTE_LCORE_VAR_LCORE_VALUE(0, handle)), 0); \
+	     (lcore_id) < RTE_MAX_LCORE;				\
+	     (lcore_id)++, (value) = RTE_LCORE_VAR_LCORE_VALUE(lcore_id, \
+							       handle))
+
+/**
+ * Allocate space in the per-lcore id buffers for an lcore variable.
+ *
+ * The pointer returned is only an opaque identifier of the variable. To
+ * get an actual pointer to a particular instance of the variable use
+ * @ref RTE_LCORE_VAR_VALUE or @ref RTE_LCORE_VAR_LCORE_VALUE.
+ *
+ * The lcore variable values' memory is set to zero.
+ *
+ * The allocation is always successful, barring a fatal exhaustion of
+ * the per-lcore id buffer space.
+ *
+ * rte_lcore_var_alloc() is not multi-thread safe.
+ *
+ * @param size
+ *   The size (in bytes) of the variable's per-lcore id value. Must be > 0.
+ * @param align
+ *   If 0, the values will be suitably aligned for any kind of type
+ *   (i.e., alignof(max_align_t)). Otherwise, the values will be aligned
+ *   on a multiple of *align*, which must be a power of 2 and equal or
+ *   less than @c RTE_CACHE_LINE_SIZE.
+ * @return
+ *   The variable's handle, stored in a void pointer value. The value
+ *   is always non-NULL.
+ */
+__rte_experimental
+void *
+rte_lcore_var_alloc(size_t size, size_t align);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _RTE_LCORE_VAR_H_ */
diff --git a/lib/eal/version.map b/lib/eal/version.map
index e3ff412683..77d3181087 100644
--- a/lib/eal/version.map
+++ b/lib/eal/version.map
@@ -396,6 +396,9 @@ EXPERIMENTAL {
 
 	# added in 24.03
 	rte_vfio_get_device_info; # WINDOWS_NO_EXPORT
+
+	# added in 24.11
+	rte_lcore_var_alloc;
 };
 
 INTERNAL {
-- 
2.43.0