Date: Mon, 08 May 2006 05:13:00 +0200 From: des@des.no (Dag-Erling =?iso-8859-1?Q?Sm=F8rgrav?=) To: "Vincent Blondel" <vincent@xtra-net.org> Cc: freebsd-current@freebsd.org Subject: Re: I_686 MMX / 3DNOW / SSE / SSE2 ? Message-ID: <86d5epp5tv.fsf@xps.des.no> In-Reply-To: <61809.192.168.1.21.1147030254.squirrel@192.168.1.21> (Vincent Blondel's message of "Sun, 7 May 2006 21:30:54 %2B0200 (CEST)") References: <61809.192.168.1.21.1147030254.squirrel@192.168.1.21>
next in thread | previous in thread | raw e-mail | index | archive | help
"Vincent Blondel" <vincent@xtra-net.org> writes: > So in this context, I use 'CFLAGS=3D -O2 -pipe -fno-strict-aliasing' > and 'CPUTYPE?=3Dathlon-xp' for compiling kernel but when I look at > file /usr/src/sys/conf/kern.mk I see all kind of mmx/3dnow/sse/sse2 > are disabled [...] We don't want to use floating point within the kernel, for a variety of reasons (one of them being that saving and restoring the floating point context when switching in and out of the kernel is very expensive). > So, finally, there is something I don't understand, what is the goal > of 'CPU_ENABLE_SSE' [...] The (now standard) CPU_ENABLE_SSE option adds code to save / restore SSE registers when necesary. This allows userland applications to use SSE without getting clobbering eachother's data. DES --=20 Dag-Erling Sm=F8rgrav - des@des.no
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?86d5epp5tv.fsf>