From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 80E01C54EE9 for ; Tue, 20 Sep 2022 22:18:41 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4MXGCg4bHgz3cBV for ; Wed, 21 Sep 2022 08:18:39 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=kernel.crashing.org (client-ip=63.228.1.57; helo=gate.crashing.org; envelope-from=segher@kernel.crashing.org; receiver=) Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) by lists.ozlabs.org (Postfix) with ESMTP id 4MXGCC4sBBz2xmr for ; Wed, 21 Sep 2022 08:18:14 +1000 (AEST) Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 28KMG8nd010624; Tue, 20 Sep 2022 17:16:08 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 28KMG8L6010623; Tue, 20 Sep 2022 17:16:08 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Tue, 20 Sep 2022 17:16:08 -0500 From: Segher Boessenkool To: Nicholas Piggin Subject: Re: [RFC PATCH 5/7] powerpc/64s: update generic cpu option name and compiler flags Message-ID: <20220920221608.GB25951@gate.crashing.org> References: <20220919140149.4018927-1-npiggin@gmail.com> <20220919140149.4018927-6-npiggin@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220919140149.4018927-6-npiggin@gmail.com> User-Agent: Mutt/1.4.2.3i X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linuxppc-dev@lists.ozlabs.org, Alan Modra Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Hi! On Tue, Sep 20, 2022 at 12:01:47AM +1000, Nicholas Piggin wrote: > Update the 64s GENERIC_CPU option. POWER4 support has been dropped, so > make that clear in the option name. AFAIR the minimum now is POWER4+ (ISA 2.01), not POWER5 (ISA 2.02). > -mtune= before power8 is dropped because the minimum gcc version > supports power8, and tuning is made consistent between big and little > endian. Tuning for p8 on e.g. 970 gives quite bad results. No idea if anyone cares, but this is a serious regression if so. > Big endian drops -mcpu=power4 in favour of power5. Effectively the > minimum compiler version means power5 was always being selected here, > so this should not change anything. 970 / G5 code generation does not > seem to have been a problem with -mcpu=power5, but it's possible we > should go back to power4 to be really safe. Yes, -mcpu=power5 code does *not* run on 970, if you are unlucky enough that the compiler does something smart with popcntb (the sole non-float insn new on p5, not counting hrfid). > +# -mcpu=power5 should generate 970 compatible kernel code It doesn't. Even if it did, it would need more explanation! Segher