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


From: Scott Wood
Subject: Re: [Qemu-devel] [PATCH 12/15] openpic: IRQ_check: search the queue a word at a time
Date: Thu, 3 Jan 2013 14:32:03 -0600

On 01/03/2013 02:31:30 PM, Alexander Graf wrote:


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.

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

-Scott



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