Re: [PATCH 1/3] hpsa: remove unneeded loop

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On Thu, Aug 01, 2013 at 03:11:22PM +0200, Tomas Henzl wrote:
> From: Tomas Henzl <thenzl@xxxxxxxxxx>
> 
> The cmd_pool_bits is protected everywhere with a spinlock, 
> we don't need the test_and_set_bit, set_bit is enough and the loop
> can be removed too.
> 
> Signed-off-by: Tomas Henzl <thenzl@xxxxxxxxxx>
> ---
>  drivers/scsi/hpsa.c | 15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/scsi/hpsa.c b/drivers/scsi/hpsa.c
> index 796482b..d7df01e 100644
> --- a/drivers/scsi/hpsa.c
> +++ b/drivers/scsi/hpsa.c
> @@ -2662,15 +2662,12 @@ static struct CommandList *cmd_alloc(struct ctlr_info *h)
>  	unsigned long flags;
>  
>  	spin_lock_irqsave(&h->lock, flags);
> -	do {
> -		i = find_first_zero_bit(h->cmd_pool_bits, h->nr_cmds);
> -		if (i == h->nr_cmds) {
> -			spin_unlock_irqrestore(&h->lock, flags);
> -			return NULL;
> -		}
> -	} while (test_and_set_bit
> -		 (i & (BITS_PER_LONG - 1),
> -		  h->cmd_pool_bits + (i / BITS_PER_LONG)) != 0);
> +	i = find_first_zero_bit(h->cmd_pool_bits, h->nr_cmds);
> +	if (i == h->nr_cmds) {
> +		spin_unlock_irqrestore(&h->lock, flags);
> +		return NULL;
> +	}
> +	set_bit(i & (BITS_PER_LONG - 1), h->cmd_pool_bits + (i / BITS_PER_LONG));
>  	h->nr_allocs++;
>  	spin_unlock_irqrestore(&h->lock, flags);
>  
> -- 
> 1.8.3.1
> 

Would it be better instead to just not use the spinlock for protecting
cmd_pool_bits?  I have thought about doing this for awhile, but haven't
gotten around to it.

I think the while loop is safe without the spin lock.  And then it is
not needed in cmd_free either.

-- steve

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