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Subject[tip: perf/core] lib: Introduce generic min-heap
The following commit has been merged into the perf/core branch of tip:

Commit-ID: 6e24628d78e4785385876125cba62315ca3b04b9
Gitweb: https://git.kernel.org/tip/6e24628d78e4785385876125cba62315ca3b04b9
Author: Ian Rogers <irogers@google.com>
AuthorDate: Thu, 13 Feb 2020 23:51:29 -08:00
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Fri, 06 Mar 2020 11:56:59 +01:00

lib: Introduce generic min-heap

Supports push, pop and converting an array into a heap. If the sense of
the compare function is inverted then it can provide a max-heap.

Based-on-work-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200214075133.181299-3-irogers@google.com
---
include/linux/min_heap.h | 134 ++++++++++++++++++++++++++-
lib/Kconfig.debug | 10 ++-
lib/Makefile | 1 +-
lib/test_min_heap.c | 194 ++++++++++++++++++++++++++++++++++++++-
4 files changed, 339 insertions(+)
create mode 100644 include/linux/min_heap.h
create mode 100644 lib/test_min_heap.c

diff --git a/include/linux/min_heap.h b/include/linux/min_heap.h
new file mode 100644
index 0000000..4407783
--- /dev/null
+++ b/include/linux/min_heap.h
@@ -0,0 +1,134 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_MIN_HEAP_H
+#define _LINUX_MIN_HEAP_H
+
+#include <linux/bug.h>
+#include <linux/string.h>
+#include <linux/types.h>
+
+/**
+ * struct min_heap - Data structure to hold a min-heap.
+ * @data: Start of array holding the heap elements.
+ * @nr: Number of elements currently in the heap.
+ * @size: Maximum number of elements that can be held in current storage.
+ */
+struct min_heap {
+ void *data;
+ int nr;
+ int size;
+};
+
+/**
+ * struct min_heap_callbacks - Data/functions to customise the min_heap.
+ * @elem_size: The nr of each element in bytes.
+ * @less: Partial order function for this heap.
+ * @swp: Swap elements function.
+ */
+struct min_heap_callbacks {
+ int elem_size;
+ bool (*less)(const void *lhs, const void *rhs);
+ void (*swp)(void *lhs, void *rhs);
+};
+
+/* Sift the element at pos down the heap. */
+static __always_inline
+void min_heapify(struct min_heap *heap, int pos,
+ const struct min_heap_callbacks *func)
+{
+ void *left, *right, *parent, *smallest;
+ void *data = heap->data;
+
+ for (;;) {
+ if (pos * 2 + 1 >= heap->nr)
+ break;
+
+ left = data + ((pos * 2 + 1) * func->elem_size);
+ parent = data + (pos * func->elem_size);
+ smallest = parent;
+ if (func->less(left, smallest))
+ smallest = left;
+
+ if (pos * 2 + 2 < heap->nr) {
+ right = data + ((pos * 2 + 2) * func->elem_size);
+ if (func->less(right, smallest))
+ smallest = right;
+ }
+ if (smallest == parent)
+ break;
+ func->swp(smallest, parent);
+ if (smallest == left)
+ pos = (pos * 2) + 1;
+ else
+ pos = (pos * 2) + 2;
+ }
+}
+
+/* Floyd's approach to heapification that is O(nr). */
+static __always_inline
+void min_heapify_all(struct min_heap *heap,
+ const struct min_heap_callbacks *func)
+{
+ int i;
+
+ for (i = heap->nr / 2; i >= 0; i--)
+ min_heapify(heap, i, func);
+}
+
+/* Remove minimum element from the heap, O(log2(nr)). */
+static __always_inline
+void min_heap_pop(struct min_heap *heap,
+ const struct min_heap_callbacks *func)
+{
+ void *data = heap->data;
+
+ if (WARN_ONCE(heap->nr <= 0, "Popping an empty heap"))
+ return;
+
+ /* Place last element at the root (position 0) and then sift down. */
+ heap->nr--;
+ memcpy(data, data + (heap->nr * func->elem_size), func->elem_size);
+ min_heapify(heap, 0, func);
+}
+
+/*
+ * Remove the minimum element and then push the given element. The
+ * implementation performs 1 sift (O(log2(nr))) and is therefore more
+ * efficient than a pop followed by a push that does 2.
+ */
+static __always_inline
+void min_heap_pop_push(struct min_heap *heap,
+ const void *element,
+ const struct min_heap_callbacks *func)
+{
+ memcpy(heap->data, element, func->elem_size);
+ min_heapify(heap, 0, func);
+}
+
+/* Push an element on to the heap, O(log2(nr)). */
+static __always_inline
+void min_heap_push(struct min_heap *heap, const void *element,
+ const struct min_heap_callbacks *func)
+{
+ void *data = heap->data;
+ void *child, *parent;
+ int pos;
+
+ if (WARN_ONCE(heap->nr >= heap->size, "Pushing on a full heap"))
+ return;
+
+ /* Place at the end of data. */
+ pos = heap->nr;
+ memcpy(data + (pos * func->elem_size), element, func->elem_size);
+ heap->nr++;
+
+ /* Sift child at pos up. */
+ for (; pos > 0; pos = (pos - 1) / 2) {
+ child = data + (pos * func->elem_size);
+ parent = data + ((pos - 1) / 2) * func->elem_size;
+ if (func->less(parent, child))
+ break;
+ func->swp(parent, child);
+ }
+}
+
+#endif /* _LINUX_MIN_HEAP_H */
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 69def4a..f04b61c 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1769,6 +1769,16 @@ config TEST_LIST_SORT

If unsure, say N.

+config TEST_MIN_HEAP
+ tristate "Min heap test"
+ depends on DEBUG_KERNEL || m
+ help
+ Enable this to turn on min heap function tests. This test is
+ executed only once during system boot (so affects only boot time),
+ or at module load time.
+
+ If unsure, say N.
+
config TEST_SORT
tristate "Array-based sort test"
depends on DEBUG_KERNEL || m
diff --git a/lib/Makefile b/lib/Makefile
index 611872c..09a8acb 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -67,6 +67,7 @@ CFLAGS_test_ubsan.o += $(call cc-disable-warning, vla)
UBSAN_SANITIZE_test_ubsan.o := y
obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
obj-$(CONFIG_TEST_LIST_SORT) += test_list_sort.o
+obj-$(CONFIG_TEST_MIN_HEAP) += test_min_heap.o
obj-$(CONFIG_TEST_LKM) += test_module.o
obj-$(CONFIG_TEST_VMALLOC) += test_vmalloc.o
obj-$(CONFIG_TEST_OVERFLOW) += test_overflow.o
diff --git a/lib/test_min_heap.c b/lib/test_min_heap.c
new file mode 100644
index 0000000..d19c808
--- /dev/null
+++ b/lib/test_min_heap.c
@@ -0,0 +1,194 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define pr_fmt(fmt) "min_heap_test: " fmt
+
+/*
+ * Test cases for the min max heap.
+ */
+
+#include <linux/log2.h>
+#include <linux/min_heap.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+#include <linux/random.h>
+
+static __init bool less_than(const void *lhs, const void *rhs)
+{
+ return *(int *)lhs < *(int *)rhs;
+}
+
+static __init bool greater_than(const void *lhs, const void *rhs)
+{
+ return *(int *)lhs > *(int *)rhs;
+}
+
+static __init void swap_ints(void *lhs, void *rhs)
+{
+ int temp = *(int *)lhs;
+
+ *(int *)lhs = *(int *)rhs;
+ *(int *)rhs = temp;
+}
+
+static __init int pop_verify_heap(bool min_heap,
+ struct min_heap *heap,
+ const struct min_heap_callbacks *funcs)
+{
+ int *values = heap->data;
+ int err = 0;
+ int last;
+
+ last = values[0];
+ min_heap_pop(heap, funcs);
+ while (heap->nr > 0) {
+ if (min_heap) {
+ if (last > values[0]) {
+ pr_err("error: expected %d <= %d\n", last,
+ values[0]);
+ err++;
+ }
+ } else {
+ if (last < values[0]) {
+ pr_err("error: expected %d >= %d\n", last,
+ values[0]);
+ err++;
+ }
+ }
+ last = values[0];
+ min_heap_pop(heap, funcs);
+ }
+ return err;
+}
+
+static __init int test_heapify_all(bool min_heap)
+{
+ int values[] = { 3, 1, 2, 4, 0x8000000, 0x7FFFFFF, 0,
+ -3, -1, -2, -4, 0x8000000, 0x7FFFFFF };
+ struct min_heap heap = {
+ .data = values,
+ .nr = ARRAY_SIZE(values),
+ .size = ARRAY_SIZE(values),
+ };
+ struct min_heap_callbacks funcs = {
+ .elem_size = sizeof(int),
+ .less = min_heap ? less_than : greater_than,
+ .swp = swap_ints,
+ };
+ int i, err;
+
+ /* Test with known set of values. */
+ min_heapify_all(&heap, &funcs);
+ err = pop_verify_heap(min_heap, &heap, &funcs);
+
+
+ /* Test with randomly generated values. */
+ heap.nr = ARRAY_SIZE(values);
+ for (i = 0; i < heap.nr; i++)
+ values[i] = get_random_int();
+
+ min_heapify_all(&heap, &funcs);
+ err += pop_verify_heap(min_heap, &heap, &funcs);
+
+ return err;
+}
+
+static __init int test_heap_push(bool min_heap)
+{
+ const int data[] = { 3, 1, 2, 4, 0x80000000, 0x7FFFFFFF, 0,
+ -3, -1, -2, -4, 0x80000000, 0x7FFFFFFF };
+ int values[ARRAY_SIZE(data)];
+ struct min_heap heap = {
+ .data = values,
+ .nr = 0,
+ .size = ARRAY_SIZE(values),
+ };
+ struct min_heap_callbacks funcs = {
+ .elem_size = sizeof(int),
+ .less = min_heap ? less_than : greater_than,
+ .swp = swap_ints,
+ };
+ int i, temp, err;
+
+ /* Test with known set of values copied from data. */
+ for (i = 0; i < ARRAY_SIZE(data); i++)
+ min_heap_push(&heap, &data[i], &funcs);
+
+ err = pop_verify_heap(min_heap, &heap, &funcs);
+
+ /* Test with randomly generated values. */
+ while (heap.nr < heap.size) {
+ temp = get_random_int();
+ min_heap_push(&heap, &temp, &funcs);
+ }
+ err += pop_verify_heap(min_heap, &heap, &funcs);
+
+ return err;
+}
+
+static __init int test_heap_pop_push(bool min_heap)
+{
+ const int data[] = { 3, 1, 2, 4, 0x80000000, 0x7FFFFFFF, 0,
+ -3, -1, -2, -4, 0x80000000, 0x7FFFFFFF };
+ int values[ARRAY_SIZE(data)];
+ struct min_heap heap = {
+ .data = values,
+ .nr = 0,
+ .size = ARRAY_SIZE(values),
+ };
+ struct min_heap_callbacks funcs = {
+ .elem_size = sizeof(int),
+ .less = min_heap ? less_than : greater_than,
+ .swp = swap_ints,
+ };
+ int i, temp, err;
+
+ /* Fill values with data to pop and replace. */
+ temp = min_heap ? 0x80000000 : 0x7FFFFFFF;
+ for (i = 0; i < ARRAY_SIZE(data); i++)
+ min_heap_push(&heap, &temp, &funcs);
+
+ /* Test with known set of values copied from data. */
+ for (i = 0; i < ARRAY_SIZE(data); i++)
+ min_heap_pop_push(&heap, &data[i], &funcs);
+
+ err = pop_verify_heap(min_heap, &heap, &funcs);
+
+ heap.nr = 0;
+ for (i = 0; i < ARRAY_SIZE(data); i++)
+ min_heap_push(&heap, &temp, &funcs);
+
+ /* Test with randomly generated values. */
+ for (i = 0; i < ARRAY_SIZE(data); i++) {
+ temp = get_random_int();
+ min_heap_pop_push(&heap, &temp, &funcs);
+ }
+ err += pop_verify_heap(min_heap, &heap, &funcs);
+
+ return err;
+}
+
+static int __init test_min_heap_init(void)
+{
+ int err = 0;
+
+ err += test_heapify_all(true);
+ err += test_heapify_all(false);
+ err += test_heap_push(true);
+ err += test_heap_push(false);
+ err += test_heap_pop_push(true);
+ err += test_heap_pop_push(false);
+ if (err) {
+ pr_err("test failed with %d errors\n", err);
+ return -EINVAL;
+ }
+ pr_info("test passed\n");
+ return 0;
+}
+module_init(test_min_heap_init);
+
+static void __exit test_min_heap_exit(void)
+{
+ /* do nothing */
+}
+module_exit(test_min_heap_exit);
+
+MODULE_LICENSE("GPL");
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