lib: test module for find_*_bit() functions

find_bit functions are widely used in the kernel, including hot paths.
This module tests performance of those 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
	find_next_bit:          240043 cycles,  164062 iterations
	find_next_zero_bit:     312848 cycles,  163619 iterations
	find_last_bit:          193748 cycles,  164062 iterations
	find_first_bit:      177720874 cycles,  164062 iterations

	 Start testing find_bit() with sparse bitmap
	find_next_bit:            3633 cycles,     656 iterations
	find_next_zero_bit:     620399 cycles,  327025 iterations
	find_last_bit:            3038 cycles,     656 iterations
	find_first_bit:         691407 cycles,     656 iterations

[arnd@arndb.de: use correct format string for find-bit tests]
Link: http://lkml.kernel.org/r/20171113135605.3166307-1-arnd@arndb.de
Link: http://lkml.kernel.org/r/20171109140714.13168-1-ynorov@caviumnetworks.com
Signed-off-by: Yury Norov <ynorov@caviumnetworks.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Clement Courbet <courbet@google.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 8ffd891857aba74eb4c309c692e6ae7034bd4a7b..ce813731269f6c1318feaf0ce1656b2454b90d1c 100644 (file)
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1850,6 +1850,15 @@ 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 e3cb2a2413380aa7d70d65ca11689aea6ea261bf..d11c48ec8ffdbd32db32cf9258c8bb45e92e440b 100644 (file)
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -47,6 +47,7 @@ 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 (file)
index 0000000..f4394a3
--- /dev/null
+++ b/lib/test_find_bit.c
@@ -0,0 +1,144 @@
+/*
+ * 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%llu cycles,\t%ld iterations\n",
+              (u64)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%llu cycles,\t%ld iterations\n",
+              (u64)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%llu cycles,\t%ld iterations\n",
+              (u64)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%llu cycles,\t%ld iterations\n",
+              (u64)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");