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

[Alexander Graf]

Am 03.01.2013 um 21:07 schrieb Scott Wood <address@hidden>:

> 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 <address@hidden>
>> 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.


Alex

> 
> -Scott