[PATCH v10 2/5] ptr_compress: add pointer compression library

[Paul Szczepanek <paul.szczepanek@arm.com>]

Add a new utility header for compressing pointers. The provided
functions can store pointers in 32-bit or 16-bit offsets.

The compression takes advantage of the fact that pointers are
usually located in a limited memory region (like a mempool).
We can compress them by converting them to offsets from a base
memory address. Offsets can be stored in fewer bytes (dictated
by the memory region size and alignment of the pointer).
For example: an 8 byte aligned pointer which is part of a 32GB
memory pool can be stored in 4 bytes.

Suggested-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Signed-off-by: Paul Szczepanek <paul.szczepanek@arm.com>
Signed-off-by: Kamalakshitha Aligeri <kamalakshitha.aligeri@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Reviewed-by: Nathan Brown <nathan.brown@arm.com>
---
 MAINTAINERS                            |   4 +
 doc/api/doxy-api-index.md              |   1 +
 doc/api/doxy-api.conf.in               |   1 +
 doc/guides/rel_notes/release_24_03.rst |   6 +
 lib/meson.build                        |   1 +
 lib/ptr_compress/meson.build           |   4 +
 lib/ptr_compress/rte_ptr_compress.h    | 266 +++++++++++++++++++++++++
 7 files changed, 283 insertions(+)
 create mode 100644 lib/ptr_compress/meson.build
 create mode 100644 lib/ptr_compress/rte_ptr_compress.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 4755a68274..6f703b1b13 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1685,6 +1685,10 @@ M: Chenbo Xia <chenbox@nvidia.com>
 M: Gaetan Rivet <grive@u256.net>
 F: lib/pci/

+Pointer Compression
+M: Paul Szczepanek <paul.szczepanek@arm.com>
+F: lib/ptr_compress/
+
 Power management
 M: Anatoly Burakov <anatoly.burakov@intel.com>
 M: David Hunt <david.hunt@intel.com>
diff --git a/doc/api/doxy-api-index.md b/doc/api/doxy-api-index.md
index 8c1eb8fafa..f9283154f8 100644
--- a/doc/api/doxy-api-index.md
+++ b/doc/api/doxy-api-index.md
@@ -222,6 +222,7 @@ The public API headers are grouped by topics:
   [config file](@ref rte_cfgfile.h),
   [key/value args](@ref rte_kvargs.h),
   [argument parsing](@ref rte_argparse.h),
+  [ptr_compress](@ref rte_ptr_compress.h),
   [string](@ref rte_string_fns.h),
   [thread](@ref rte_thread.h)

diff --git a/doc/api/doxy-api.conf.in b/doc/api/doxy-api.conf.in
index 27afec8b3b..a8823c046f 100644
--- a/doc/api/doxy-api.conf.in
+++ b/doc/api/doxy-api.conf.in
@@ -71,6 +71,7 @@ INPUT                   = @TOPDIR@/doc/api/doxy-api-index.md \
                           @TOPDIR@/lib/pipeline \
                           @TOPDIR@/lib/port \
                           @TOPDIR@/lib/power \
+                          @TOPDIR@/lib/ptr_compress \
                           @TOPDIR@/lib/rawdev \
                           @TOPDIR@/lib/rcu \
                           @TOPDIR@/lib/regexdev \
diff --git a/doc/guides/rel_notes/release_24_03.rst b/doc/guides/rel_notes/release_24_03.rst
index 932688ca4d..b82b8c5c0b 100644
--- a/doc/guides/rel_notes/release_24_03.rst
+++ b/doc/guides/rel_notes/release_24_03.rst
@@ -176,6 +176,12 @@ New Features
   * Added power-saving during polling within the ``rte_event_dequeue_burst()`` API.
   * Added support for DMA adapter.

+* **Introduced pointer compression library.**
+
+  Library provides functions to compress and decompress arrays of pointers
+  which can improve application performance under certain conditions.
+  Performance test was added to help users evaluate performance on their setup.
+

 Removed Items
 -------------
diff --git a/lib/meson.build b/lib/meson.build
index 7c90602bf5..63becee142 100644
--- a/lib/meson.build
+++ b/lib/meson.build
@@ -14,6 +14,7 @@ libraries = [
         'argparse',
         'telemetry', # basic info querying
         'eal', # everything depends on eal
+        'ptr_compress',
         'ring',
         'rcu', # rcu depends on ring
         'mempool',
diff --git a/lib/ptr_compress/meson.build b/lib/ptr_compress/meson.build
new file mode 100644
index 0000000000..e92706a45f
--- /dev/null
+++ b/lib/ptr_compress/meson.build
@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright(c) 2024 Arm Limited
+
+headers = files('rte_ptr_compress.h')
diff --git a/lib/ptr_compress/rte_ptr_compress.h b/lib/ptr_compress/rte_ptr_compress.h
new file mode 100644
index 0000000000..97c084003d
--- /dev/null
+++ b/lib/ptr_compress/rte_ptr_compress.h
@@ -0,0 +1,266 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2024 Arm Limited
+ */
+
+#ifndef RTE_PTR_COMPRESS_H
+#define RTE_PTR_COMPRESS_H
+
+/**
+ * @file
+ * Pointer compression and decompression functions.
+ *
+ * When passing arrays full of pointers between threads, memory containing
+ * the pointers is copied multiple times which is especially costly between
+ * cores. These functions allow us to compress the pointers.
+ *
+ * Compression takes advantage of the fact that pointers are usually located in
+ * a limited memory region (like a mempool). We compress them by converting them
+ * to offsets from a base memory address. Offsets can be stored in fewer bytes.
+ *
+ * The compression functions come in two varieties: 32-bit and 16-bit.
+ *
+ * To determine how many bits are needed to compress the pointer calculate
+ * the biggest offset possible (highest value pointer - base pointer)
+ * and shift the value right according to alignment (shift by exponent of the
+ * power of 2 of alignment: aligned by 4 - shift by 2, aligned by 8 - shift by
+ * 3, etc.). The resulting value must fit in either 32 or 16 bits.
+ *
+ * For usage example and further explanation please see "Pointer Compression" in
+ * doc/guides/prog_guide/ptr_compress_lib.rst
+ */
+
+#include <stdint.h>
+#include <inttypes.h>
+
+#include <rte_branch_prediction.h>
+#include <rte_common.h>
+#include <rte_debug.h>
+#include <rte_vect.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * Compress pointers into 32-bit offsets from base pointer.
+ *
+ * @note It is programmer's responsibility to ensure the resulting offsets fit
+ * into 32 bits. Alignment of the structures pointed to by the pointers allows
+ * us to drop bits from the offsets. This is controlled by the bit_shift
+ * parameter. This means that if structures are aligned by 8 bytes they must be
+ * within 32GB of the base pointer. If there is no such alignment guarantee they
+ * must be within 4GB.
+ *
+ * @param ptr_base
+ *   A pointer used to calculate offsets of pointers in src_table.
+ * @param src_table
+ *   A pointer to an array of pointers.
+ * @param dest_table
+ *   A pointer to an array of compressed pointers returned by this function.
+ * @param n
+ *   The number of objects to compress, must be strictly positive.
+ * @param bit_shift
+ *   Byte alignment of memory pointed to by the pointers allows for
+ *   bits to be dropped from the offset and hence widen the memory region that
+ *   can be covered. This controls how many bits are right shifted.
+ **/
+static __rte_always_inline void
+rte_ptr_compress_32(void *ptr_base, void **src_table,
+		uint32_t *dest_table, size_t n, uint8_t bit_shift)
+{
+	unsigned int i = 0;
+#if defined RTE_HAS_SVE_ACLE && !defined RTE_ARCH_ARMv8_AARCH32
+	svuint64_t v_ptr_table;
+	svbool_t pg = svwhilelt_b64(i, n);
+	do {
+		v_ptr_table = svld1_u64(pg, (uint64_t *)src_table + i);
+		v_ptr_table = svsub_x(pg, v_ptr_table, (uint64_t)ptr_base);
+		v_ptr_table = svlsr_x(pg, v_ptr_table, bit_shift);
+		svst1w(pg, &dest_table[i], v_ptr_table);
+		i += svcntd();
+		pg = svwhilelt_b64(i, n);
+	} while (i < n);
+#elif defined __ARM_NEON && !defined RTE_ARCH_ARMv8_AARCH32
+	uint64_t ptr_diff;
+	uint64x2_t v_ptr_table;
+	/* right shift is done by left shifting by negative int */
+	int64x2_t v_shift = vdupq_n_s64(-bit_shift);
+	uint64x2_t v_ptr_base = vdupq_n_u64((uint64_t)ptr_base);
+	for (; i < (n & ~0x1); i += 2) {
+		v_ptr_table = vld1q_u64((const uint64_t *)src_table + i);
+		v_ptr_table = vsubq_u64(v_ptr_table, v_ptr_base);
+		v_ptr_table = vshlq_u64(v_ptr_table, v_shift);
+		vst1_u32(dest_table + i, vqmovn_u64(v_ptr_table));
+	}
+	/* process leftover single item in case of odd number of n */
+	if (unlikely(n & 0x1)) {
+		ptr_diff = RTE_PTR_DIFF(src_table[i], ptr_base);
+		dest_table[i] = (uint32_t) (ptr_diff >> bit_shift);
+	}
+#else
+	uintptr_t ptr_diff;
+	for (; i < n; i++) {
+		ptr_diff = RTE_PTR_DIFF(src_table[i], ptr_base);
+		ptr_diff = ptr_diff >> bit_shift;
+		RTE_ASSERT(ptr_diff <= UINT32_MAX);
+		dest_table[i] = (uint32_t) ptr_diff;
+	}
+#endif
+}
+
+/**
+ * Decompress pointers from 32-bit offsets from base pointer.
+ *
+ * @param ptr_base
+ *   A pointer which was used to calculate offsets in src_table.
+ * @param src_table
+ *   A pointer to an array to compressed pointers.
+ * @param dest_table
+ *   A pointer to an array of decompressed pointers returned by this function.
+ * @param n
+ *   The number of objects to decompress, must be strictly positive.
+ * @param bit_shift
+ *   Byte alignment of memory pointed to by the pointers allows for
+ *   bits to be dropped from the offset and hence widen the memory region that
+ *   can be covered. This controls how many bits are left shifted when pointers
+ *   are recovered from the offsets.
+ **/
+static __rte_always_inline void
+rte_ptr_decompress_32(void *ptr_base, uint32_t *src_table,
+		void **dest_table, size_t n, uint8_t bit_shift)
+{
+	unsigned int i = 0;
+#if defined RTE_HAS_SVE_ACLE && !defined RTE_ARCH_ARMv8_AARCH32
+	svuint64_t v_ptr_table;
+	svbool_t pg = svwhilelt_b64(i, n);
+	do {
+		v_ptr_table = svld1uw_u64(pg, &src_table[i]);
+		v_ptr_table = svlsl_x(pg, v_ptr_table, bit_shift);
+		v_ptr_table = svadd_x(pg, v_ptr_table, (uint64_t)ptr_base);
+		svst1(pg, (uint64_t *)dest_table + i, v_ptr_table);
+		i += svcntd();
+		pg = svwhilelt_b64(i, n);
+	} while (i < n);
+#elif defined __ARM_NEON && !defined RTE_ARCH_ARMv8_AARCH32
+	uint64_t ptr_diff;
+	uint64x2_t v_ptr_table;
+	int64x2_t v_shift = vdupq_n_s64(bit_shift);
+	uint64x2_t v_ptr_base = vdupq_n_u64((uint64_t)ptr_base);
+	for (; i < (n & ~0x1); i += 2) {
+		v_ptr_table = vmovl_u32(vld1_u32(src_table + i));
+		v_ptr_table = vshlq_u64(v_ptr_table, v_shift);
+		v_ptr_table = vaddq_u64(v_ptr_table, v_ptr_base);
+		vst1q_u64((uint64_t *)dest_table + i, v_ptr_table);
+	}
+	/* process leftover single item in case of odd number of n */
+	if (unlikely(n & 0x1)) {
+		ptr_diff = ((uint64_t) src_table[i]) << bit_shift;
+		dest_table[i] = RTE_PTR_ADD(ptr_base, ptr_diff);
+	}
+#else
+	uintptr_t ptr_diff;
+	for (; i < n; i++) {
+		ptr_diff = ((uintptr_t) src_table[i]) << bit_shift;
+		dest_table[i] = RTE_PTR_ADD(ptr_base, ptr_diff);
+	}
+#endif
+}
+
+/**
+ * Compress pointers into 16-bit offsets from base pointer.
+ *
+ * @note It is programmer's responsibility to ensure the resulting offsets fit
+ * into 16 bits. Alignment of the structures pointed to by the pointers allows
+ * us to drop bits from the offsets. This is controlled by the bit_shift
+ * parameter. This means that if structures are aligned by 8 bytes they must be
+ * within 256KB of the base pointer. If there is no such alignment guarantee
+ * they must be within 64KB.
+ *
+ * @param ptr_base
+ *   A pointer used to calculate offsets of pointers in src_table.
+ * @param src_table
+ *   A pointer to an array of pointers.
+ * @param dest_table
+ *   A pointer to an array of compressed pointers returned by this function.
+ * @param n
+ *   The number of objects to compress, must be strictly positive.
+ * @param bit_shift
+ *   Byte alignment of memory pointed to by the pointers allows for
+ *   bits to be dropped from the offset and hence widen the memory region that
+ *   can be covered. This controls how many bits are right shifted.
+ **/
+static __rte_always_inline void
+rte_ptr_compress_16(void *ptr_base, void **src_table,
+		uint16_t *dest_table, size_t n, uint8_t bit_shift)
+{
+
+	unsigned int i = 0;
+#if defined RTE_HAS_SVE_ACLE && !defined RTE_ARCH_ARMv8_AARCH32
+	svuint64_t v_ptr_table;
+	svbool_t pg = svwhilelt_b64(i, n);
+	do {
+		v_ptr_table = svld1_u64(pg, (uint64_t *)src_table + i);
+		v_ptr_table = svsub_x(pg, v_ptr_table, (uint64_t)ptr_base);
+		v_ptr_table = svlsr_x(pg, v_ptr_table, bit_shift);
+		svst1h(pg, &dest_table[i], v_ptr_table);
+		i += svcntd();
+		pg = svwhilelt_b64(i, n);
+	} while (i < n);
+#else
+	uintptr_t ptr_diff;
+	for (; i < n; i++) {
+		ptr_diff = RTE_PTR_DIFF(src_table[i], ptr_base);
+		ptr_diff = ptr_diff >> bit_shift;
+		RTE_ASSERT(ptr_diff <= UINT16_MAX);
+		dest_table[i] = (uint16_t) ptr_diff;
+	}
+#endif
+}
+
+/**
+ * Decompress pointers from 16-bit offsets from base pointer.
+ *
+ * @param ptr_base
+ *   A pointer which was used to calculate offsets in src_table.
+ * @param src_table
+ *   A pointer to an array to compressed pointers.
+ * @param dest_table
+ *   A pointer to an array of decompressed pointers returned by this function.
+ * @param n
+ *   The number of objects to decompress, must be strictly positive.
+ * @param bit_shift
+ *   Byte alignment of memory pointed to by the pointers allows for
+ *   bits to be dropped from the offset and hence widen the memory region that
+ *   can be covered. This controls how many bits are left shifted when pointers
+ *   are recovered from the offsets.
+ **/
+static __rte_always_inline void
+rte_ptr_decompress_16(void *ptr_base, uint16_t *src_table,
+		void **dest_table, size_t n, uint8_t bit_shift)
+{
+	unsigned int i = 0;
+#if defined RTE_HAS_SVE_ACLE && !defined RTE_ARCH_ARMv8_AARCH32
+	svuint64_t v_ptr_table;
+	svbool_t pg = svwhilelt_b64(i, n);
+	do {
+		v_ptr_table = svld1uh_u64(pg, &src_table[i]);
+		v_ptr_table = svlsl_x(pg, v_ptr_table, bit_shift);
+		v_ptr_table = svadd_x(pg, v_ptr_table, (uint64_t)ptr_base);
+		svst1(pg, (uint64_t *)dest_table + i, v_ptr_table);
+		i += svcntd();
+		pg = svwhilelt_b64(i, n);
+	} while (i < n);
+#else
+	uintptr_t ptr_diff;
+	for (; i < n; i++) {
+		ptr_diff = ((uintptr_t) src_table[i]) << bit_shift;
+		dest_table[i] = RTE_PTR_ADD(ptr_base, ptr_diff);
+	}
+#endif
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* RTE_PTR_COMPRESS_H */
--
2.25.1