find_bit functions are widely used in the kernel, including hot paths.
This module tests performance of that functions in 2 typical scenarios:
randomly filled bitmap with relatively equal distribution of set and
cleared bits, and sparse bitmap which has 1 set bit for 500 cleared bits.
On ThunderX machine:
Start testing find_bit() with random-filled bitmap
[1032111.632383] find_next_bit: 240043 cycles, 164062 iterations
[1032111.647236] find_next_zero_bit: 312848 cycles, 163619 iterations
[1032111.661585] find_last_bit: 193748 cycles, 164062 iterations
[1032113.450517] find_first_bit: 177720874 cycles, 164062
iterations
[1032113.462930]
Start testing find_bit() with sparse bitmap
[1032113.477229] find_next_bit: 3633 cycles, 656 iterations
[1032113.494281] find_next_zero_bit: 620399 cycles, 327025 iterations
[1032113.506723] find_last_bit: 3038 cycles, 656 iterations
[1032113.524485] find_first_bit: 691407 cycles, 656 iterations
v2:
- pretty printing;
- increase length of bitmap to suppress noise;
- drop inlining _find_next_bit();
CC: Alexey Dobriyan <adobri...@gmail.com>
CC: Andrew Morton <a...@linux-foundation.org>
CC: Clement Courbet <cour...@google.com>
CC: Matthew Wilcox <mawil...@microsoft.com>
CC: Rasmus Villemoes <li...@rasmusvillemoes.dk>
Signed-off-by: Yury Norov <yno...@caviumnetworks.com>
---
lib/Kconfig.debug | 9 ++++
lib/Makefile | 1 +
lib/test_find_bit.c | 141 ++++++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 151 insertions(+)
create mode 100644 lib/test_find_bit.c
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index dfdad67d8f6c..138034cc68a3 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1838,6 +1838,15 @@ config TEST_BPF
If unsure, say N.
+config TEST_FIND_BIT
+ tristate "Test find_bit functions"
+ default n
+ help
+ This builds the "test_find_bit" module that measure find_*_bit()
+ functions performance.
+
+ If unsure, say N.
+
config TEST_FIRMWARE
tristate "Test firmware loading via userspace interface"
default n
diff --git a/lib/Makefile b/lib/Makefile
index b8f2c16fccaa..97ec69d843f2 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -46,6 +46,7 @@ obj-y += hexdump.o
obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o
obj-y += kstrtox.o
obj-$(CONFIG_TEST_BPF) += test_bpf.o
+obj-$(CONFIG_TEST_FIND_BIT) += test_find_bit.o
obj-$(CONFIG_TEST_FIRMWARE) += test_firmware.o
obj-$(CONFIG_TEST_SYSCTL) += test_sysctl.o
obj-$(CONFIG_TEST_HASH) += test_hash.o test_siphash.o
diff --git a/lib/test_find_bit.c b/lib/test_find_bit.c
new file mode 100644
index 000000000000..920d5a0ca456
--- /dev/null
+++ b/lib/test_find_bit.c
@@ -0,0 +1,141 @@
+/*
+ * Test for find_*_bit functions.
+ *
+ * Copyright (c) 2017 Cavium.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ */
+
+/*
+ * find_bit functions are widely used in kernel, so the successful boot
+ * is good enough test for correctness.
+ *
+ * This test is focused on performance of traversing bitmaps. Two typical
+ * scenarios are reproduced:
+ * - randomly filled bitmap with approximately equal number of set and
+ * cleared bits;
+ * - sparse bitmap with few set bits at random positions.
+ */
+
+#include <linux/bitops.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+#include <linux/random.h>
+
+#define BITMAP_LEN (4096UL * 8 * 10)
+#define SPARSE 500
+
+static DECLARE_BITMAP(bitmap, BITMAP_LEN) __initdata;
+
+/*
+ * This is Schlemiel the Painter's algorithm. It should be called after
+ * all other tests for the same bitmap because it sets all bits of bitmap to 1.
+ */
+static int __init test_find_first_bit(void *bitmap, unsigned long len)
+{
+ unsigned long i, cnt;
+ cycles_t cycles;
+
+ cycles = get_cycles();
+ for (cnt = i = 0; i < len; cnt++) {
+ i = find_first_bit(bitmap, len);
+ __clear_bit(i, bitmap);
+ }
+ cycles = get_cycles() - cycles;
+ pr_err("find_first_bit:\t\t%ld cycles,\t%ld iterations\n", cycles, cnt);
+
+ return 0;
+}
+
+static int __init test_find_next_bit(const void *bitmap, unsigned long len)
+{
+ unsigned long i, cnt;
+ cycles_t cycles;
+
+ cycles = get_cycles();
+ for (cnt = i = 0; i < BITMAP_LEN; cnt++)
+ i = find_next_bit(bitmap, BITMAP_LEN, i) + 1;
+ cycles = get_cycles() - cycles;
+ pr_err("find_next_bit:\t\t%ld cycles,\t%ld iterations\n", cycles, cnt);
+
+ return 0;
+}
+
+static int __init test_find_next_zero_bit(const void *bitmap, unsigned long
len)
+{
+ unsigned long i, cnt;
+ cycles_t cycles;
+
+ cycles = get_cycles();
+ for (cnt = i = 0; i < BITMAP_LEN; cnt++)
+ i = find_next_zero_bit(bitmap, len, i) + 1;
+ cycles = get_cycles() - cycles;
+ pr_err("find_next_zero_bit:\t%ld cycles,\t%ld iterations\n",
+ cycles, cnt);
+
+ return 0;
+}
+
+static int __init test_find_last_bit(const void *bitmap, unsigned long len)
+{
+ unsigned long l, cnt = 0;
+ cycles_t cycles;
+
+ cycles = get_cycles();
+ do {
+ cnt++;
+ l = find_last_bit(bitmap, len);
+ if (l >= len)
+ break;
+ len = l;
+ } while (len);
+ cycles = get_cycles() - cycles;
+ pr_err("find_last_bit:\t\t%ld cycles,\t%ld iterations\n", cycles, cnt);
+
+ return 0;
+}
+
+static int __init find_bit_test(void)
+{
+ unsigned long nbits = BITMAP_LEN / SPARSE;
+
+ pr_err("\nStart testing find_bit() with random-filled bitmap\n");
+
+ get_random_bytes(bitmap, sizeof(bitmap));
+
+ test_find_next_bit(bitmap, BITMAP_LEN);
+ test_find_next_zero_bit(bitmap, BITMAP_LEN);
+ test_find_last_bit(bitmap, BITMAP_LEN);
+ test_find_first_bit(bitmap, BITMAP_LEN);
+
+ pr_err("\nStart testing find_bit() with sparse bitmap\n");
+
+ bitmap_zero(bitmap, BITMAP_LEN);
+
+ while (nbits--)
+ __set_bit(prandom_u32() % BITMAP_LEN, bitmap);
+
+ test_find_next_bit(bitmap, BITMAP_LEN);
+ test_find_next_zero_bit(bitmap, BITMAP_LEN);
+ test_find_last_bit(bitmap, BITMAP_LEN);
+ test_find_first_bit(bitmap, BITMAP_LEN);
+
+ return 0;
+}
+module_init(find_bit_test);
+
+static void __exit test_find_bit_cleanup(void)
+{
+}
+module_exit(test_find_bit_cleanup);
+
+MODULE_LICENSE("GPL");
--
2.11.0
