Date: Tue, 17 Jul 2001 19:34:21 +0200 From: Stefan Hoffmeister <freebsd-ml@econos.de> To: tlambert2@mindspring.com Cc: "Albert D. Cahalan" <acahalan@cs.uml.edu>, freebsd-hackers@FreeBSD.ORG, Jim.Pirzyk@disney.com Subject: Re: math library difference between linux emulation and native freebsd (and native linux) Message-ID: <pit8lt8464pe1enjp9jmtkt5s2hjo2v9po@4ax.com> In-Reply-To: <3B546BA9.37E9F437@mindspring.com> References: <200107170615.f6H6FU5376195@saturn.cs.uml.edu> <3B546BA9.37E9F437@mindspring.com>
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: On Tue, 17 Jul 2001 09:45:29 -0700, Terry Lambert wrote: >One obvious reason that the Linux approach is wrong is >that it ends up requiring the save and restore of FP >registers on context switches, which is overhead they >ate anyway, by doing TSS based context switching. The >amount of state with SSE is up to something like an >additional 512 bytes -- that's ungodly overhead, since >most programs don't use this context at all. Except that - AFAIK - Linux won't do that. Linux install traps, causing the first FPU and SSE instruction to fault (might as well be only the SSE instructions). Upon the fault, the context structure size is switched. IOW, Linux does not blindly have an FPU context size of 512 bytes. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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