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=-8.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 2E6C7C433DF for ; Fri, 9 Oct 2020 08:52:20 +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 A802A22272 for ; Fri, 9 Oct 2020 08:52:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="B2JLKez5" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A802A22272 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com 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=OoDxMxumZKE+cO202Dc3GxyTMvylGk3k9dx+9kbM4Sk=; b=B2JLKez5flenJhKxlK9W2qyST CBQDIQskwhrLTDuVmVzMaQi0SSJakl0Cghp4dCmdj3PGDZ8Tp4NJNRXv0AE+aSr5yetn0pjmyiil3 4zbjUJ+xx8egtqqpqSl6tyK32UJYU1LySCPIvKmleQi0IslSIsudkYBMUWu2sZH8LF57Md4O0pR7b TjRN/co4301a7Nb5nD+mJOkFI/UJbODw/2jYrNSnL8lCNnBkEd3MN1t/jkQC+ZfZRjz/E9KJINLVM cUd44rzi1uL7/OdmE8DtPlMRC0YIFj4kTKPLjt3sth5qjgj44DPpkFRNRkt2OTA/eFwom56t0I55+ mhDRSzuqQ==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kQo7G-0006cF-K5; Fri, 09 Oct 2020 08:51:06 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kQo7C-0006b9-Nu for linux-arm-kernel@lists.infradead.org; Fri, 09 Oct 2020 08:51:04 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 3E707D6E; Fri, 9 Oct 2020 01:51:01 -0700 (PDT) Received: from e123083-lin (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DE0393F66B; Fri, 9 Oct 2020 01:50:59 -0700 (PDT) Date: Fri, 9 Oct 2020 10:50:57 +0200 From: Morten Rasmussen To: Will Deacon Subject: Re: [RFC PATCH 3/3] arm64: Handle AArch32 tasks running on non AArch32 cpu Message-ID: <20201009085057.GB8004@e123083-lin> References: <20201008181641.32767-1-qais.yousef@arm.com> <20201008181641.32767-4-qais.yousef@arm.com> <20201009072943.GD2628@hirez.programming.kicks-ass.net> <20201009081312.GA8004@e123083-lin> <20201009083146.GA29594@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20201009083146.GA29594@willie-the-truck> User-Agent: Mutt/1.9.4 (2018-02-28) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201009_045102_946445_EFDD620A X-CRM114-Status: GOOD ( 34.53 ) 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, Greg Kroah-Hartman , Peter Zijlstra , Marc Zyngier , Catalin Marinas , Linus Torvalds , Qais Yousef , 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 Fri, Oct 09, 2020 at 09:31:47AM +0100, Will Deacon wrote: > On Fri, Oct 09, 2020 at 10:13:12AM +0200, Morten Rasmussen wrote: > > On Fri, Oct 09, 2020 at 09:29:43AM +0200, Peter Zijlstra wrote: > > > On Thu, Oct 08, 2020 at 07:16:41PM +0100, Qais Yousef wrote: > > > > diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c > > > > index cf94cc248fbe..7e97f1589f33 100644 > > > > --- a/arch/arm64/kernel/signal.c > > > > +++ b/arch/arm64/kernel/signal.c > > > > @@ -908,13 +908,28 @@ static void do_signal(struct pt_regs *regs) > > > > restore_saved_sigmask(); > > > > } > > > > > > > > +static void set_32bit_cpus_allowed(void) > > > > { > > > > + cpumask_var_t cpus_allowed; > > > > + int ret = 0; > > > > + > > > > + if (cpumask_subset(current->cpus_ptr, &aarch32_el0_mask)) > > > > + return; > > > > + > > > > /* > > > > + * On asym aarch32 systems, if the task has invalid cpus in its mask, > > > > + * we try to fix it by removing the invalid ones. > > > > */ > > > > + if (!alloc_cpumask_var(&cpus_allowed, GFP_ATOMIC)) { > > > > + ret = -ENOMEM; > > > > + } else { > > > > + cpumask_and(cpus_allowed, current->cpus_ptr, &aarch32_el0_mask); > > > > + ret = set_cpus_allowed_ptr(current, cpus_allowed); > > > > + free_cpumask_var(cpus_allowed); > > > > + } > > > > + > > > > + if (ret) { > > > > + pr_warn_once("Failed to fixup affinity of running 32-bit task\n"); > > > > force_sig(SIGKILL); > > > > } > > > > } > > > > > > Yeah, no. Not going to happen. > > > > > > Fundamentally, you're not supposed to change the userspace provided > > > affinity mask. If we want to do something like this, we'll have to teach > > > the scheduler about this second mask such that it can compute an > > > effective mask as the intersection between the 'feature' and user mask. > > > > I agree that we shouldn't mess wit the user-space mask directly. Would it > > be unthinkable to go down the route of maintaining a new mask which is > > the intersection of the feature mask (controlled and updated by arch > > code) and the user-space mask? > > > > It shouldn't add overhead in the scheduler as it would use the > > intersection mask instead of the user-space mask, the main complexity > > would be around making sure the intersection mask is updated correctly > > (cpusets, hotplug, ...). > > > > Like the above tweak, this won't help if the intersection mask is empty, > > task will still get killed but it will allow tasks to survive > > user-space masks including some non-compatible CPUs. If we want to > > prevent task killing in all cases (ignoring hotplug) it gets more ugly > > as we would have to ignore the user-space mask in some cases. > > Honestly, I don't understand why we're trying to hide this asymmetry from > userspace by playing games with affinity masks in the kernel. Userspace > is likely to want to move things about _anyway_ because even amongst the > 32-bit capable cores, you may well have different clock frequencies to > contend with. I agree it doesn't make sense to hide the asymmetry. The only argument I see for tweaking the affinity is to be more friendly in case user-space is unaware. > So I'd be *much* happier to let the schesduler do its thing, and if one > of these 32-bit tasks ends up on a core that can't deal with it, then > tough, it gets killed. Give userspace the information it needs to avoid > that happening in the first place, rather than implicitly limit the mask. > > That way, the kernel support really boils down to two parts: > > 1. Remove the sanity checks we have to prevent 32-bit applications running > on asymmetric systems > > 2. Tell userspace about the problem I'm fine with that. We just have to accept that existing unaware user-space(s) may see tasks getting killed if they use task affinity. Morten _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel