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Subject[PATCH 24/34] mISDN: optimize get_free_devid()
Date
get_free_devid() traverses each bit in device_ids in an open-coded loop.
We can do it faster by using 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:

ffs();
test_and_set_bit().

Signed-off-by: Yury Norov <yury.norov@gmail.com>
---
drivers/isdn/mISDN/core.c | 9 ++-------
1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/isdn/mISDN/core.c b/drivers/isdn/mISDN/core.c
index ab8513a7acd5..3f97db006cf3 100644
--- a/drivers/isdn/mISDN/core.c
+++ b/drivers/isdn/mISDN/core.c
@@ -197,14 +197,9 @@ get_mdevice_count(void)
static int
get_free_devid(void)
{
- u_int i;
+ u_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
--
2.39.2
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