2014-12-28 16:12:49

by Aniroop Mathur

Subject: [PATCH] s390: Initialize nr_devices count variable to -1

From: Aniroop Mathur <[email protected]>

This patch initializes nr_device count variable to -1 to avoid extra
subtraction operation performed everytime scm block device is set up.

Signed-off-by: Aniroop Mathur <[email protected]>
---
drivers/s390/block/scm_blk.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/block/scm_blk.c b/drivers/s390/block/scm_blk.c
index 76bed17..ee2bd6f 100644
--- a/drivers/s390/block/scm_blk.c
+++ b/drivers/s390/block/scm_blk.c
@@ -23,7 +23,7 @@ static int scm_major;
static DEFINE_SPINLOCK(list_lock);
static LIST_HEAD(inactive_requests);
static unsigned int nr_requests = 64;
-static atomic_t nr_devices = ATOMIC_INIT(0);
+static atomic_t nr_devices = ATOMIC_INIT(-1);
module_param(nr_requests, uint, S_IRUGO);
MODULE_PARM_DESC(nr_requests, "Number of parallel requests.");

@@ -357,7 +357,7 @@ int scm_blk_dev_setup(struct scm_blk_dev *bdev, struct scm_device *scmdev)
int len, ret = -ENOMEM;
unsigned int devindex, nr_max_blk;

- devindex = atomic_inc_return(&nr_devices) - 1;
+ devindex = atomic_inc_return(&nr_devices);
/* scma..scmz + scmaa..scmzz */
if (devindex > 701) {
ret = -ENODEV;
--
1.9.1

2014-12-29 09:56:14

by Martin Schwidefsky

Subject: Re: [PATCH] s390: Initialize nr_devices count variable to -1

On Sun, 28 Dec 2014 21:42:53 +0530
Aniroop Mathur <[email protected]> wrote:

> From: Aniroop Mathur <[email protected]>
>
> This patch initializes nr_device count variable to -1 to avoid extra
> subtraction operation performed everytime scm block device is set up.
>
> Signed-off-by: Aniroop Mathur <[email protected]>
> ---
> drivers/s390/block/scm_blk.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/s390/block/scm_blk.c b/drivers/s390/block/scm_blk.c
> index 76bed17..ee2bd6f 100644
> --- a/drivers/s390/block/scm_blk.c
> +++ b/drivers/s390/block/scm_blk.c
> @@ -23,7 +23,7 @@ static int scm_major;
> static DEFINE_SPINLOCK(list_lock);
> static LIST_HEAD(inactive_requests);
> static unsigned int nr_requests = 64;
> -static atomic_t nr_devices = ATOMIC_INIT(0);
> +static atomic_t nr_devices = ATOMIC_INIT(-1);
> module_param(nr_requests, uint, S_IRUGO);
> MODULE_PARM_DESC(nr_requests, "Number of parallel requests.");
>
> @@ -357,7 +357,7 @@ int scm_blk_dev_setup(struct scm_blk_dev *bdev, struct scm_device *scmdev)
> int len, ret = -ENOMEM;
> unsigned int devindex, nr_max_blk;
>
> - devindex = atomic_inc_return(&nr_devices) - 1;
> + devindex = atomic_inc_return(&nr_devices);
> /* scma..scmz + scmaa..scmzz */
> if (devindex > 701) {
> ret = -ENODEV;

This patch makes the code harder to read to avoid a single subtraction at
device setup time. I prefer readability.

--
blue skies,
Martin.

"Reality continues to ruin my life." - Calvin.