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 4C54AC38A02 for ; Sat, 29 Oct 2022 15:37:23 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4N03Sd3XNBz3cNj for ; Sun, 30 Oct 2022 02:37:21 +1100 (AEDT) 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 4N03Rz6fpdz3bhl for ; Sun, 30 Oct 2022 02:36:45 +1100 (AEDT) Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 29TFXYnV001845; Sat, 29 Oct 2022 10:33:34 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 29TFXVDQ001842; Sat, 29 Oct 2022 10:33:31 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Sat, 29 Oct 2022 10:33:31 -0500 From: Segher Boessenkool To: Christian Zigotzky Subject: Re: Issues with the first PowerPC updates for the kernel 6.1 Message-ID: <20221029153331.GI25951@gate.crashing.org> References: <87y1tfl1pt.fsf@mpe.ellerman.id.au> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: 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: Darren Stevens , Andrew Donnellan , npiggin@gmail.com, rmclure@linux.ibm.com, mad skateman , Olof Johansson , linuxppc-dev , Trevor Dickinson , Christian Zigotzky Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Mon, Oct 17, 2022 at 09:53:04AM +0200, Christian Zigotzky wrote: > > On 17. Oct 2022, at 02:43, Michael Ellerman wrote: > > Previously BIG_ENDIAN && GENERIC_CPU would use -mcpu=power5, now it uses > > -mcpu=power4. > > Maybe this is the issue. We will wait and not release the RC1 for testing because it is a risk for our testers to test these new kernels because of this issue. > > It is really important do not to rewrite code, that is well worked before. > Bugfixing and adding some new features is ok but rewriting of good code is expensive and doesn’t make any sense. It was just a bugfix, and a (partial) revert. 471d7ff8b51b says it removed ISA 2.00 support (original power4, "GP"). Support for ISA 2.01 was retained it says. That is power4+, "GQ", but also 970 (Apple G5). That patch actually switched to ISA 2.02 though, unintendedly, and code generated for ISA 2.02 will not run on systems like 970, in principle. It is just one uncommon instruction that is problematical, namely popcntb, because the kernel does not use floating point at all, so that is why we got away with it for so long (most code that does use fp will fall flat on its face in no time). It still is a bug fix though! PA6T is ISA 2.04, it's not clear how this (bugfix, and revert!) change made code not run on PA6T anymore. Smells a lot like something indirect (or triply indirect), a separate bug, something that was introduced in the last two years maybe, but I'll even bet it is something *exposed* in that time, a bug that has been here for longer! Segher