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lib/find_bit_benchmark: avoid clearing randomly filled bitmap in test_find_first_bit()

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test_find_first_bit() searches for a set bit from the beginning of the
test bitmap and clears it repeatedly, eventually clearing the entire
bitmap.

After test_find_first_bit() is executed, test_find_first_and_bit() and
test_find_next_and_bit() are executed without randomly reinitializing the
cleared bitmap.

In the first phase (testing find_bit() with a random-filled bitmap),
test_find_first_bit() only operates on 1/10 of the entire size of the
testing bitmap, so this isn't a big problem.

However, in the second phase (testing find_bit() with a sparse bitmap),
test_find_first_bit() clears the entire test bitmap, so the subsequent
test_find_first_and_bit() and test_find_next_and_bit() will not find any
set bits. This is probably not the intended benchmark.

To fix this issue, test_find_first_bit() operates on a duplicated bitmap
and does not clear the original test bitmap.
The same is already done in test_find_first_and_bit().

While we're at it, add const qualifiers to the bitmap pointer arguments
in the test functions.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Yury Norov <ynorov@nvidia.com>
This commit is contained in:
Akinobu Mita
2026-03-11 00:21:26 +09:00
committed by Yury Norov
parent a676643709
commit 6c88ba561c
1 changed files with 9 additions and 6 deletions
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15
lib/find_bit_benchmark.c
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@@ -30,18 +30,20 @@ static DECLARE_BITMAP(bitmap, BITMAP_LEN) __initdata;
static DECLARE_BITMAP(bitmap2, 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.
* This is Schlemiel the Painter's algorithm.
*/
static int __init test_find_first_bit(void *bitmap, unsigned long len)
static int __init test_find_first_bit(const void *bitmap, unsigned long len)
{
static DECLARE_BITMAP(cp, BITMAP_LEN) __initdata;
unsigned long i, cnt;
ktime_t time;
bitmap_copy(cp, bitmap, BITMAP_LEN);
time = ktime_get();
for (cnt = i = 0; i < len; cnt++) {
i = find_first_bit(bitmap, len);
__clear_bit(i, bitmap);
i = find_first_bit(cp, len);
__clear_bit(i, cp);
}
time = ktime_get() - time;
pr_err("find_first_bit: %18llu ns, %6ld iterations\n", time, cnt);
@@ -49,7 +51,8 @@ static int __init test_find_first_bit(void *bitmap, unsigned long len)
return 0;
}
static int __init test_find_first_and_bit(void *bitmap, const void *bitmap2, unsigned long len)
static int __init test_find_first_and_bit(const void *bitmap, const void *bitmap2,
unsigned long len)
{
static DECLARE_BITMAP(cp, BITMAP_LEN) __initdata;
unsigned long i, cnt;