Date: Sun, 21 Mar 1999 12:06:28 -0500 (EST) From: zhihuizhang <bf20761@binghamton.edu> To: Luigi Rizzo <luigi@labinfo.iet.unipi.it> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: Calculation of load average and CCPU_SHIFT Message-ID: <Pine.SOL.L3.93.990321120025.21143A-100000@bingsun2> In-Reply-To: <199903201819.TAA02543@labinfo.iet.unipi.it>
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On Sat, 20 Mar 1999, Luigi Rizzo wrote: > > I am looking into the source code in file vm_meter.c and kern_synch.c of > > FreeBSD 2.2.8. They use integer multiplication and shift operation to > > replace the costly float multiplication. The FSCALE and FSHIFT are for > > it is not only costly (actually, on modern CPUs it is not costly at > all!), FPU usage is not allowed in the kernel. > I have never heard of this. Can you explain a little bit more on why FPU usage is not allowed in the kernel or give me pointers where I can find more information on this topic? For the rest of my original question, I guess that it uses "fixed-point arithmetic". Thanks a lot. -Zhihui To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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