In case the call side is not providing a swap function, we either use
a 32 bit or a generic swap function. When swapping around pointers on
64 bit architectures falling back to use the generic swap function
seems like an unnecessary waste.
There at least 9 users ('sort' is of difficult to grep for) of sort()
and all of them use the sort function without a customized swap
function. Furthermore, they are all using pointers to swap around:
arch/x86/kernel/e820.c:sanitize_e820_map()
arch/x86/mm/extable.c:sort_extable()
drivers/acpi/fan.c:acpi_fan_get_fps()
fs/btrfs/super.c:btrfs_descending_sort_devices()
fs/xfs/libxfs/xfs_dir2_block.c:xfs_dir2_sf_to_block()
kernel/range.c:clean_sort_range()
mm/memcontrol.c:__mem_cgroup_usage_register_event()
sound/pci/hda/hda_auto_parser.c:snd_hda_parse_pin_defcfg()
sound/pci/hda/hda_auto_parser.c:sort_pins_by_sequence()
Obviously, we could improve the swap for other sizes as well
but this is overkill at this point.
A simple test shows sorting a 400 element array (try to stay in one
page) with either with u32_swap() or u64_swap() show that the theory
actually works. This test was done on a x86_64 (Intel Xeon E5-4610)
machine.
$ cat u32_swap.old | histogram.py
NumSamples = 99; Min = 26.00; Max = 37.00
Mean = 28.494949; Variance = 1.542904; SD = 1.242137; Median 28.000000
each ∎ represents a count of 1
26.0000 - 27.1000 [ 13]: ∎∎∎∎∎∎∎∎∎∎∎∎∎
27.1000 - 28.2000 [ 44]: ∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎
28.2000 - 29.3000 [ 28]: ∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎
29.3000 - 30.4000 [ 13]: ∎∎∎∎∎∎∎∎∎∎∎∎∎
30.4000 - 31.5000 [ 0]:
31.5000 - 32.6000 [ 0]:
32.6000 - 33.7000 [ 0]:
33.7000 - 34.8000 [ 0]:
34.8000 - 35.9000 [ 0]:
35.9000 - 37.0000 [ 1]: ∎
$ cat u32_swap.new | histogram.py
NumSamples = 99; Min = 26.00; Max = 28.00
Mean = 27.030303; Variance = 0.191001; SD = 0.437037; Median 27.000000
each ∎ represents a count of 1
26.0000 - 26.2000 [ 8]: ∎∎∎∎∎∎∎∎
26.2000 - 26.4000 [ 0]:
26.4000 - 26.6000 [ 0]:
26.6000 - 26.8000 [ 0]:
26.8000 - 27.0000 [ 80]:
∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎
27.0000 - 27.2000 [ 0]:
27.2000 - 27.4000 [ 0]:
27.4000 - 27.6000 [ 0]:
27.6000 - 27.8000 [ 0]:
27.8000 - 28.0000 [ 11]: ∎∎∎∎∎∎∎∎∎∎∎
$ cat u64_swap.old | histogram.py
NumSamples = 99; Min = 43.00; Max = 45.00
Mean = 44.060606; Variance = 0.137741; SD = 0.371135; Median 44.000000
each ∎ represents a count of 1
43.0000 - 43.2000 [ 4]: ∎∎∎∎
43.2000 - 43.4000 [ 0]:
43.4000 - 43.6000 [ 0]:
43.6000 - 43.8000 [ 0]:
43.8000 - 44.0000 [ 85]:
∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎
44.0000 - 44.2000 [ 0]:
44.2000 - 44.4000 [ 0]:
44.4000 - 44.6000 [ 0]:
44.6000 - 44.8000 [ 0]:
44.8000 - 45.0000 [ 10]: ∎∎∎∎∎∎∎∎∎∎
$ cat u64_swap.new | histogram.py
NumSamples = 99; Min = 26.00; Max = 32.00
Mean = 26.939394; Variance = 0.400367; SD = 0.632746; Median 27.000000
each ∎ represents a count of 1
26.0000 - 26.6000 [ 13]: ∎∎∎∎∎∎∎∎∎∎∎∎∎
26.6000 - 27.2000 [ 83]:
∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎∎
27.2000 - 27.8000 [ 0]:
27.8000 - 28.4000 [ 2]: ∎∎
28.4000 - 29.0000 [ 0]:
29.0000 - 29.6000 [ 0]:
29.6000 - 30.2000 [ 0]:
30.2000 - 30.8000 [ 0]:
30.8000 - 31.4000 [ 0]:
31.4000 - 32.0000 [ 1]: ∎
Signed-off-by: Daniel Wagner <daniel.wag...@bmw-carit.de>
Cc: Rasmus Villemoes <li...@rasmusvillemoes.dk>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org
---
#include <linux/sort.h>
#include <linux/random.h>
#include <linux/ktime.h>
#include <linux/printk.h>
#include <linux/slab.h>
#include <linux/module.h>
#define ARRAY_ELEMENTS 400
static int cmp_32(const void *a, const void *b)
{
return (int) (*(u32 *)a - *(u32 *)b);
}
static int cmp_64(const void *a, const void *b)
{
return (int) (*(u64 *)a - *(u64 *)b);
}
static void init_array32(void *array)
{
u32 *a = array;
int i;
a[0] = 3821;
for (i = 1; i < ARRAY_ELEMENTS; i++)
a[i] = next_pseudo_random32(a[i-1]);
}
static void init_array64(void *array)
{
u64 *a = array;
int i;
a[0] = 3821;
for (i = 1; i < ARRAY_ELEMENTS; i++)
a[i] = next_pseudo_random32(a[i-1]);
}
static void sort_test(size_t size, void *array)
{
int (*cmp) (const void *, const void *);
void (*init)(void *array);
ktime_t start, stop;
int i;
if (size == 4) {
init = init_array32;
cmp = cmp_32;
} else if (size == 8) {
init = init_array64;
cmp = cmp_64;
} else
return;
for (i = 0; i < 10000; i++) {
init(array);
local_irq_disable();
start = ktime_get();
sort(array, ARRAY_ELEMENTS, size, cmp, NULL);
stop = ktime_get();
local_irq_enable();
if (i > 10000 - 100)
pr_info("%lld\n", ktime_to_us(ktime_sub(stop, start)));
}
}
static void *create_array(size_t size)
{
void *array;
array = kmalloc(ARRAY_ELEMENTS * size, GFP_KERNEL);
if (!array)
return NULL;
return array;
}
static int perform_test(size_t size)
{
void *array;
array = create_array(size);
if (!array)
return -ENOMEM;
pr_info("test u%d_swap\n", (int)size * 8);
sort_test(size, array);
kfree(array);
return 0;
}
static int __init sort_tests_init(void)
{
int err;
err = perform_test(sizeof(u32));
if (err)
return err;
err = perform_test(sizeof(u64));
if (err)
return err;
return 0;
}
static void __exit sort_tests_exit(void)
{
}
module_init(sort_tests_init);
module_exit(sort_tests_exit);
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR("Daniel Wagner");
MODULE_DESCRIPTION("sort perfomance tests");
lib/sort.c | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)
diff --git a/lib/sort.c b/lib/sort.c
index 43c9fe7..86e3efe 100644
--- a/lib/sort.c
+++ b/lib/sort.c
@@ -15,6 +15,13 @@ static void u32_swap(void *a, void *b, int size)
*(u32 *)b = t;
}
+static void u64_swap(void *a, void *b, int size)
+{
+ u64 t = *(u64 *)a;
+ *(u64 *)a = *(u64 *)b;
+ *(u64 *)b = t;
+}
+
static void generic_swap(void *a, void *b, int size)
{
char t;
@@ -50,8 +57,18 @@ void sort(void *base, size_t num, size_t size,
/* pre-scale counters for performance */
int i = (num/2 - 1) * size, n = num * size, c, r;
- if (!swap_func)
- swap_func = (size == 4 ? u32_swap : generic_swap);
+ if (!swap_func) {
+ switch (size) {
+ case 4:
+ swap_func = u32_swap;
+ break;
+ case 8:
+ swap_func = u64_swap;
+ break;
+ default:
+ swap_func = generic_swap;
+ }
+ }
/* heapify */
for ( ; i >= 0; i -= size) {
--
2.1.0
--
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