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Date: Thu, 10 Jan 2002 12:42:19 -0800
From: george anzinger <george@mvista.com>
Organization: Monta Vista Software
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To: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
CC: Anton Blanchard <anton@samba.org>, Ingo Molnar <mingo@elte.hu>,
        Linus Torvalds <torvalds@transmeta.com>,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [patch] O(1) scheduler, -D1, 2.5.2-pre9, 2.4.17
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Ivan Kokshaysky wrote:
> 
> On Wed, Jan 09, 2002 at 05:09:28PM -0800, Richard Henderson wrote:
> > Careful.  The following is really quite a bit better on Alpha:
> >
> > static inline int
> > sched_find_first_zero_bit(unsigned long *bitmap)
> > {
> >         unsigned long b0 = bitmap[0];
> >         unsigned long b1 = bitmap[1];
> >         unsigned long b2 = bitmap[2];
> >         unsigned long ofs = MAX_RT_PRIO;
> >
> >         if (unlikely(~(b0 & b1) != 0)) {
> >                 b2 = (~b0 == 0 ? b0 : b1);
> >                 ofs = (~b0 == 0 ? 0 : 64);
> >         }
> >
> >         return ffz(b2) + ofs;
> > }
> 
> True. Minor correction:
> -               b2 = (~b0 == 0 ? b0 : b1);
> -               ofs = (~b0 == 0 ? 0 : 64);
> +               b2 = (~b0 ? b0 : b1);
> +               ofs = (~b0 ? 0 : 64);
> 
> Note that comment for this function is a bit confusing:
>  * ... It's the fastest
>  * way of searching a 168-bit bitmap where the first 128 bits are
>  * unlikely to be set.

What if we want a 2048-bit bitmap???
> 
> s/set/cleared/
> 
> > While we're on the subject of sched_find_first_zero_bit, I'd
> > like to complain about Ingo's choice of header file.  Why in
> > the world did you choose mmu_context.h?  Invent a new asm/sched.h
> > if you must, but please don't choose headers at random.
> 
> Agreed. Apparently asm/bitops.h?
> 
> Ivan.
> -
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-- 
George           george@mvista.com
High-res-timers: http://sourceforge.net/projects/high-res-timers/
Real time sched: http://sourceforge.net/projects/rtsched/
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