[PATCH] dma/timberdale: simplify conditional

[PATCH] dma/timberdale: simplify conditional

[Nicolas Kaiser]

Simplify: ((a && b) || (!a && !b)) => (a == b)

Signed-off-by: Nicolas Kaiser <nikai@nikai.net>
---
 drivers/dma/timb_dma.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/dma/timb_dma.c b/drivers/dma/timb_dma.c
index 2ec1ed5..3b88a4e 100644
--- a/drivers/dma/timb_dma.c
+++ b/drivers/dma/timb_dma.c
@@ -759,7 +759,7 @@ static int __devinit td_probe(struct platform_device *pdev)
 			pdata->channels + i;
 
 		/* even channels are RX, odd are TX */
-		if (((i % 2) && pchan->rx) || (!(i % 2) && !pchan->rx)) {
+		if ((i % 2) == pchan->rx) {
 			dev_err(&pdev->dev, "Wrong channel configuration\n");
 			err = -EINVAL;
 			goto err_tasklet_kill;
-- 
1.7.2.2

Re: [PATCH] dma/timberdale: simplify conditional

[Jack Stone]

We should be careful with this sort of transformation. It is only
guaranteed true if both sides are boolean. E.g. ((foo & mask) && (bar &
baz)) ¦¦ (!(foo & mask) && (!(bar & baz)) does not imply (foo & mask) ==
(bar & baz)). foo & mask could equal 0x0100 for example but bar & baz
could equal 0x0001. Both are true as logicals but they are not equal.

One safe way to make this patch would be to add !! in front of both
halves.

Of course this is a moot point if pdes->rx is a boolean or a single bit
but I don't have the source to hand to check this (% 2 is guaranteed to
be 0 or 1 so it doesn't matter).

Sorry if this doesn't make sense. Let me know and I can try and
rephrase.

Hope this helps,
Jack

On Fri, 08 Oct 2010 00:48 +0200, "Nicolas Kaiser" <nikai@nikai.net>
wrote:
> Simplify: ((a && b) || (!a && !b)) => (a == b)
> 
> Signed-off-by: Nicolas Kaiser <nikai@nikai.net>
> ---
>  drivers/dma/timb_dma.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/dma/timb_dma.c b/drivers/dma/timb_dma.c
> index 2ec1ed5..3b88a4e 100644
> --- a/drivers/dma/timb_dma.c
> +++ b/drivers/dma/timb_dma.c
> @@ -759,7 +759,7 @@ static int __devinit td_probe(struct platform_device
> *pdev)
>  			pdata->channels + i;
>  
>  		/* even channels are RX, odd are TX */
> -               if (((i % 2) && pchan->rx) || (!(i % 2) && !pchan->rx)) {
> +               if ((i % 2) == pchan->rx) {
>  			dev_err(&pdev->dev, "Wrong channel configuration\n");
>  			err = -EINVAL;
>  			goto err_tasklet_kill;
> -- 
> 1.7.2.2
> --
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Re: [PATCH] dma/timberdale: simplify conditional

[Jack Stone]

My sincere apologies for the previous mail and the HTML email. I am
still trying to get used to a new mail client but it is no excuse.

Sorry,

Jack

driver or calculation of load average wrong ?

[Frank Salomon]

Hello All,

I have the following configuration:
- CentOS 5
- kernel 2.6.20.1
- My own driver in a kernel_thread:
		while ( 1 ){
			printk ( KERN_INFO "go sleep, %lu\n", jiffies );
			current -> state = TASK_UNINTERRUPTIBLE;
			schedule_timeout ( msecs_to_jiffies(4000) );
			printk ( KERN_INFO "wakeup, %lu\n", jiffies );
		}

Each time I load the driver, the load average in /proc/loadavg reached:
	$ cat /proc/loadavg
	0.99 0.62 0.26 1/47 2868
Without my driver:
	$ cat /proc/loadavg
	0.03 0.03 0.00 1/47 2867

I changed nr_active(void) in kernel/sched.c:
unsigned long nr_active(void)
{
         unsigned long i, running = 0, uninterruptible = 0;

         for_each_online_cpu(i) {
                 running += cpu_rq(i)->nr_running;
                 uninterruptible += cpu_rq(i)->nr_uninterruptible;
         }

         if (unlikely((long)uninterruptible < 0))
                 uninterruptible = 0;

// original:     return running + uninterruptible;
         return running;
}

Driver loaded or not:
	$ cat /proc/loadavg
	0.03 0.03 0.00 1/47 2867

Any help or comments would be really great?

Best regards, thanks, Frank




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Re: [PATCH] dma/timberdale: simplify conditional

[Jack Stone]

It's just not my day today.

I had a look on LXR and rx is defined as a bool so we're safe in this
case but might be worth a comment or even !! to future proof it.

Sorry for all the noise, Jack