[PATCH v4 25/40] mISDN: optimize get_free_devid()

Yury Norov
2024-06-20T17:58:21Z

get_free_devid() traverses each bit in device_ids in an open-coded loop.
Simplify it by using the dedicated find_and_set_bit().

It makes the whole function a nice one-liner. And because MAX_DEVICE_ID
is a small constant-time value (63), on 64-bit platforms find_and_set_bit()
call will be optimized to:

test_and_set_bit(ffs());

Signed-off-by: Yury Norov <yury.norov@gmail.com>
---
drivers/isdn/mISDN/core.c | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/drivers/isdn/mISDN/core.c b/drivers/isdn/mISDN/core.c
index ab8513a7acd5..d499b193529a 100644
--- a/drivers/isdn/mISDN/core.c
+++ b/drivers/isdn/mISDN/core.c
@@ -3,6 +3,7 @@
* Copyright 2008 by Karsten Keil <kkeil@novell.com>
*/

+#include <linux/find_atomic.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/stddef.h>
@@ -197,14 +198,9 @@ get_mdevice_count(void)
static int
get_free_devid(void)
{
- u_int i;
+ int i = find_and_set_bit((u_long *)&device_ids, MAX_DEVICE_ID + 1);

- for (i = 0; i <= MAX_DEVICE_ID; i++)
- if (!test_and_set_bit(i, (u_long *)&device_ids))
- break;
- if (i > MAX_DEVICE_ID)
- return -EBUSY;
- return i;
+ return i <= MAX_DEVICE_ID ? i : -EBUSY;
}

int
--
2.43.0