Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750707AbWJCL2Z (ORCPT ); Tue, 3 Oct 2006 07:28:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750709AbWJCL2Z (ORCPT ); Tue, 3 Oct 2006 07:28:25 -0400 Received: from outpipe-village-512-1.bc.nu ([81.2.110.250]:20928 "EHLO lxorguk.ukuu.org.uk") by vger.kernel.org with ESMTP id S1750707AbWJCL2Y (ORCPT ); Tue, 3 Oct 2006 07:28:24 -0400 Subject: Re: [PATCH/RFC] Math-emu kills the kernel on Athlon64 X2 II -- it's terminally broken From: Alan Cox To: Andi Kleen Cc: Randy Dunlap , Linus Torvalds , akpm , Jesper Juhl , Linux Kernel Mailing List In-Reply-To: <200610031211.46168.ak@suse.de> References: <9a8748490609181518j2d12e4f0l2c55e755e40d38c2@mail.gmail.com> <20061002202426.aa3ecb4f.rdunlap@xenotime.net> <200610031211.46168.ak@suse.de> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Tue, 03 Oct 2006 12:53:34 +0100 Message-Id: <1159876414.17553.29.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.6.2 (2.6.2-1.fc5.5) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1036 Lines: 22 Ar Maw, 2006-10-03 am 12:11 +0200, ysgrifennodd Andi Kleen: > On Tuesday 03 October 2006 05:24, Randy Dunlap wrote: > > Actually I looked at the code more closely. It looks like kernel math > emulation is much more broken. e.g. kernel_fpu_begin() is missing > code and lots of other paths in i387 that need to check HAVE_HWFP don't. That check would be wrong anyway. A kernel built with FPU emulation boots, runs and uses the hardware FPU code correctly. The problem area is the X86_FEATURE_foo stuff. I think that comes down to a single thing - if we have FPU disabled clear X86_FEATURE_FXSR|X86_FEATURE_MMX| X86_FEATURE_SSE* in the boot cpu features during early option parsing/setup. Basically the emulated FPU is forgetting to tell the truth about the fact its a very basic FPU. Alan - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/