From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (from majordomo@localhost) by oss.sgi.com (8.11.2/8.11.3) id g1KF03D13368 for linux-mips-outgoing; Wed, 20 Feb 2002 07:00:03 -0800 Received: from dea.linux-mips.net (a1as06-p249.stg.tli.de [195.252.187.249]) by oss.sgi.com (8.11.2/8.11.3) with SMTP id g1KExm913344 for ; Wed, 20 Feb 2002 06:59:51 -0800 Received: (from ralf@localhost) by dea.linux-mips.net (8.11.6/8.11.1) id g1KDIfO16279; Wed, 20 Feb 2002 14:18:41 +0100 Date: Wed, 20 Feb 2002 14:18:41 +0100 From: Ralf Baechle To: Jun Sun Cc: Greg Lindahl , linux-mips@oss.sgi.com Subject: Re: FPU emulator unsafe for SMP? Message-ID: <20020220141841.E15588@dea.linux-mips.net> References: <3C6C6ACF.CAD2FFC@mvista.com> <20020215031118.B21011@dea.linux-mips.net> <20020214232030.A3601@mvista.com> <20020215003037.A3670@mvista.com> <002b01c1b607$6afbd5c0$10eca8c0@grendel> <20020219140514.C25739@mvista.com> <00af01c1b9a2$c0d6d5f0$10eca8c0@grendel> <20020219171238.E25739@mvista.com> <20020219222835.A4195@wumpus.skymv.com> <20020219202434.F25739@mvista.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: <20020219202434.F25739@mvista.com>; from jsun@mvista.com on Tue, Feb 19, 2002 at 08:24:34PM -0800 X-Accept-Language: de,en,fr Sender: owner-linux-mips@oss.sgi.com Precedence: bulk On Tue, Feb 19, 2002 at 08:24:34PM -0800, Jun Sun wrote: > > What you propose, locking the fpu owner to the current cpu, will not > > result in a fair solution. Imagine a 2 cpu machine with 2 processes > > using integer math and 1 using floating point... how much cpu time > > will each process get? > > In this case, proc that uses fpu gets about 50% of one cpu, i.e., 25% of > total load, while the other two integer math proces split the rest 75%, > which gives 37.5% each. Not too bad in my opinion. Certainly not good either. Still not having checked the x86 solution I currently favor the approach of only always storing the fp context but lazily restoring it. Ralf