From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from lists.gentoo.org (pigeon.gentoo.org [208.92.234.80]) by finch.gentoo.org (Postfix) with ESMTP id A4661138989 for ; Sat, 2 May 2015 17:04:19 +0000 (UTC) Received: from pigeon.gentoo.org (localhost [127.0.0.1]) by pigeon.gentoo.org (Postfix) with SMTP id B3CEEE0887; Sat, 2 May 2015 17:04:13 +0000 (UTC) Received: from mail-wg0-f51.google.com (mail-wg0-f51.google.com [74.125.82.51]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by pigeon.gentoo.org (Postfix) with ESMTPS id 8E9F0E0854 for ; Sat, 2 May 2015 17:04:12 +0000 (UTC) Received: by wgin8 with SMTP id n8so114863800wgi.0 for ; Sat, 02 May 2015 10:04:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=googlemail.com; s=20120113; h=message-id:date:from:user-agent:mime-version:to:subject:references :in-reply-to:content-type:content-transfer-encoding; bh=Og3px5qZPqgpti/zSPYYFSZ8z0UcaMmK5XoPbGwfN1s=; b=qPdz+ngKUpA8E30t4cc5RP8sCfS/EuFB6ReyWYb5wrIGeKSFZF0a19i8Ym8Yrf7w1l fmDWzdsKLuy79iHMLXIEPIhb5OMPvAuxjjsa7MaAyV5LfdIZvzdnv/7d7tM29SXgO6eM Qd+gxod6JXYLFrv34bv1G9Tw0Gnyxfp1+keSXKpj+JJLIjW4pcRaylCr/YayXzblDVMq EBG+0Jhw/9/x2CuCQhtYubUlboSuJLYulRm6fsCa+0SaxvwB8ncoxF0OLZWz/oSiS16D +QC9TDsMr5pfrfgSJwRQEMgEjGucWhDOcX7cZB/XKRViNReR2c1FoLytwpspSgXsyOCM h5Hw== X-Received: by 10.194.118.135 with SMTP id km7mr27023073wjb.125.1430586251408; Sat, 02 May 2015 10:04:11 -0700 (PDT) Received: from [192.168.178.21] (p4FC11A75.dip0.t-ipconnect.de. [79.193.26.117]) by mx.google.com with ESMTPSA id i13sm3090376wic.13.2015.05.02.10.04.10 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 02 May 2015 10:04:10 -0700 (PDT) Message-ID: <55450389.7070900@googlemail.com> Date: Sat, 02 May 2015 19:04:09 +0200 From: Volker Armin Hemmann User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-Id: Gentoo Linux mail X-BeenThere: gentoo-user@lists.gentoo.org Reply-to: gentoo-user@lists.gentoo.org MIME-Version: 1.0 To: gentoo-user@lists.gentoo.org Subject: Re: [gentoo-user] Re: CFLAGs for kernel compilation References: <5540C101.70906@ramses-pyramidenbau.de> <20150430123819.b72d8b39bd60a912b7c7fde5@gentoo.org> <20150501104402.27d943c901f638942262d3d1@gentoo.org> <5544B2AB.1010700@googlemail.com> <5544B6F2.8040508@googlemail.com> <5544BEB9.9050103@googlemail.com> In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Archives-Salt: 7177130c-49b6-4771-b408-37dd93cbd378 X-Archives-Hash: 56f5fca20c213973f27bb5d9ae891463 Am 02.05.2015 um 14:38 schrieb Nikos Chantziaras: > On 02/05/15 15:10, Volker Armin Hemmann wrote: >> Am 02.05.2015 um 14:06 schrieb Nikos Chantziaras: >>> On 02/05/15 14:37, Volker Armin Hemmann wrote: >>>> Am 02.05.2015 um 13:25 schrieb Nikos Chantziaras: >>>>>>> >>>>>>> The kernel uses -O2 and several -march variants (e.g. >>>>>>> -march=core2). >>>>>>> Several other options are used to prevent GCC from generating >>>>>>> unsuitable code. >>>>>>> >>>>>>> Specifying another -march variant does not affect the optimizer >>>>>>> though. It only affects the code generator. If you don't modify the >>>>>>> other CFLAGS and only change -march, you will not get FP >>>>>>> instructions >>>>>>> unless you use FP in the code. >>>>>> >>>>>> http://www.agner.org/optimize/calling_conventions.pdf >>>>> >>>>> Not sure what you're trying to say. >>>>> >>>> >>>> that simd is not save in kernel if not carefully guarded. >>>> >>>> Really people, just don't fuck around with the cflags. >>> >>> I still fail to see the relevance. Unless you mean using a different >>> -O level. In that case, yes. You shouldn't. But I was talking about >>> -march. >>> >> >> you said this >> >>> >>> (note that SIMD is not FP and is perfectly fine in the kernel.) >> >> and I have shown you that you are wrong. > > Not sure why you think that. The kernel crypto routines are full of > SIMD code (like SSE and AVX.) Automatic vectorization wouldn't work. > But -march is not going to introduce that and never used in interrupt context and carefully guarded. You act like 'oh, you can use simd instructions without any consideration' and that is just not true.