Re: [Qemu-devel] [PATCH 12/15] openpic: IRQ_check: search the queue a word at a time

[Scott Wood <scottwood@freescale.com>]

On 01/03/2013 02:31:30 PM, Alexander Graf wrote:
> 
> 
> Am 03.01.2013 um 21:07 schrieb Scott Wood <scottwood@freescale.com>:
> 
> > On 01/03/2013 12:53:13 PM, Alexander Graf wrote:
> >> On 22.12.2012, at 03:15, Scott Wood wrote:
> >> > Search the queue more efficiently by first looking for a  
> non-zero word,
> >> > and then using the common bit-searching function to find the bit  
> within
> >> > the word.  It would be even nicer if bitops_ffsl() could be  
> hooked up
> >> > to the compiler intrinsic so that bit-searching instructions  
> could be
> >> > used, but that's another matter.
> >> >
> >> > Signed-off-by: Scott Wood <scottwood@freescale.com>
> >> What we really want is a bitmap wide ffs() bipops helper function  
> that returns the first set bit in a bitmap and can optimize the hell  
> out of that operation inside of itself. I don't think this belongs to  
> the OpenPIC code.
> >
> > Well, we do have find_next_bit() in bitops.c, but it looks  
> comparitively complicated in order to be generic and simply return a  
> value rather than perform an action on each bit set.  I suspect that  
> the code in this patch would be faster, and avoids the need for me to  
> follow all the twists and turns of find_next_bit() to figure out  
> whether the undocumented interface is actually exactly what I guess  
> it to be (e.g. what does it return when no bit is found?).
> 
> I would just call it bit_ffs and follow the same semantics.

I'm not sure how that's an answer to what I wrote...

-Scott