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 X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 71C9FC388F7 for ; Tue, 10 Nov 2020 10:10:46 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E5F9F20780 for ; Tue, 10 Nov 2020 10:10:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="0oZCIvKZ"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="exnBnWXD" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E5F9F20780 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=dsPv0jLiTfFuhcBdgNdxctTa+CeEa/nWXz0end3P6DA=; b=0oZCIvKZILDjweYh/rI53DtM2 6jrmk4g9gKGsAOHq8ciOAVwU12LEz8eV2iCnVkgqy1GhkpIncnPf0ARLx61jB6yM2pPTM/1ph/nGH 7yn6QxUTurcHibV8on8r98gq1jFfgIbNolvaXtSpeWPdV8Qey+c3CELeQKOFuOB4cGylDohgQHcKN aSZK9CnTMQ4SsKbc14zS8bSOHib/kHdkm2JK39or0ZHLAnIu6wtunOXIdznihf1tLfvsVB81UQX3J 8jePJm6Iq0BbQD8iPZzfTqGtKyFjNazqyBpyhOLCejgJ+IE1dVktQMvlQQTfGIuA28hiZrpf3UV7y rmfobvzww==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kcQao-0001DT-2S; Tue, 10 Nov 2020 10:09:38 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kcQak-0001CL-FC for linux-arm-kernel@lists.infradead.org; Tue, 10 Nov 2020 10:09:35 +0000 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id BDD9E20780; Tue, 10 Nov 2020 10:09:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1605002973; bh=U5aaL8w8vpGKmDmBS/BPhY5OijCIpFEEL7zAO1zMJgo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=exnBnWXD2u+O8LraGvXH6k7vWm/iKAsF4nwhXAI4she7UvOxo52piNAy+7Up7zemw lHNCOMqzygDIc/Ji3CZ4KEf1xs7O2eOZ/qB5M0m4j6tX+e4PZwBXx6Y9n/JyrHd3K/ zKVpc5AXqKAc5yzIzwqyag4jxDmmA+cfyV1ikl8o= Date: Tue, 10 Nov 2020 11:10:30 +0100 From: Greg Kroah-Hartman To: Marc Zyngier Subject: Re: [PATCH v2 5/6] arm64: Advertise CPUs capable of running 32-bit applications in sysfs Message-ID: References: <20201109213023.15092-1-will@kernel.org> <20201109213023.15092-6-will@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201110_050934_647753_30FEC172 X-CRM114-Status: GOOD ( 20.93 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, kernel-team@android.com, Quentin Perret , Peter Zijlstra , Catalin Marinas , Qais Yousef , Suren Baghdasaryan , Will Deacon , Morten Rasmussen , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Nov 10, 2020 at 09:53:53AM +0000, Marc Zyngier wrote: > On 2020-11-10 09:36, Greg Kroah-Hartman wrote: > > [...] > > > While punting the logic out to userspace is simple for the kernel, and > > of course my first option, I think this isn't going to work in the > > long-run and the kernel will have to "know" what type of process it is > > scheduling in order to correctly deal with this nightmare as userspace > > can't do that well, if at all. > > For that to happen, we must first decide which part of the userspace > ABI we are prepared to compromise on. The most obvious one would be to > allow overriding the affinity on exec, but I'm pretty sure it has bad > interactions with cgroups, on top of violating the existing ABI which > mandates that the affinity is inherited across exec. So you are saying that you have to violate this today with this patch set? Or would have to violate that if the scheduler got involved? How is userspace going to "know" how to do all of this properly? Who is going to write that code? > There may be other options (always make at least one 32bit-capable CPU > part of the process affinity?), but they all imply some form of userspace > visible regressions. > > Pick your poison... :-/ What do the system designers and users of this hardware recommend? They are the ones that dreamed up this, and seem to somehow want this. What do they think the correct solution is here as obviously they must have thought this through when designing such a beast, right? And if they didn't think any of this through then why are they wanting to run Linux on this thing? thanks, greg k-h _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel