Date: Thu, 15 Nov 2012 14:02:37 -0800 From: Juli Mallett <jmallett@FreeBSD.org> To: Warner Losh <imp@bsdimp.com> Cc: "Jayachandran C." <jchandra@freebsd.org>, "freebsd-mips@FreeBSD.org" <mips@freebsd.org>, Alan Cox <alc@rice.edu> Subject: Re: ZERO_REGION_SIZE Message-ID: <CACVs6=9ZiVeWcJUoeNU_Mybn5WgZ2edUkx4ERPEXD%2BPODp8gKw@mail.gmail.com> In-Reply-To: <DF2CB7FC-C1ED-4F4C-A39A-60B5E7FC566D@bsdimp.com> References: <50A53391.4080909@rice.edu> <CAJ-Vmon-v3K7012ti_L6ao3wQHfQ99Jau1kJ%2BGhumbPjAuSDww@mail.gmail.com> <50A54CCD.8070409@rice.edu> <DF2CB7FC-C1ED-4F4C-A39A-60B5E7FC566D@bsdimp.com>
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On Thu, Nov 15, 2012 at 1:07 PM, Warner Losh <imp@bsdimp.com> wrote: > > On Nov 15, 2012, at 1:13 PM, Alan Cox wrote: > > P.S. I would encourage someone with hardware to look into implementing a > > non-iterative ffs*() using (d)clz. The MIPS pmap would benefit from > > this. Basically, most pmap_enter() calls are doing an ffs*(). > > ffs finds the first bit set. clz counts the number of leading zeros and > thus finds the last bit set. Would a non-iterative fls* be helpful? > Right. And no widespread ctz/ffs MIPS instructions as far as I know. We could use pop/dpop on processors that support them to do non-iterative ffs*, with a few additional instructions, though.
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