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=-10.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 B837EC433E0 for ; Fri, 15 May 2020 11:51:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9BE7E206D4 for ; Fri, 15 May 2020 11:51:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726177AbgEOLvG (ORCPT ); Fri, 15 May 2020 07:51:06 -0400 Received: from lhrrgout.huawei.com ([185.176.76.210]:2212 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726062AbgEOLvG (ORCPT ); Fri, 15 May 2020 07:51:06 -0400 Received: from lhreml724-chm.china.huawei.com (unknown [172.18.7.108]) by Forcepoint Email with ESMTP id 58A4C1273F1470C21441; Fri, 15 May 2020 12:51:04 +0100 (IST) Received: from [127.0.0.1] (10.47.1.24) by lhreml724-chm.china.huawei.com (10.201.108.75) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.1913.5; Fri, 15 May 2020 12:51:01 +0100 Subject: Re: [PATCH v3 0/2] irqchip/gic-v3-its: Balance LPI affinity across CPUs To: Marc Zyngier CC: "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , Jason Cooper , "chenxiang (M)" , Robin Murphy , luojiaxing , Ming Lei , "Wangzhou (B)" , Thomas Gleixner , Will Deacon References: <20200316115433.9017-1-maz@kernel.org> <9171c554-50d2-142b-96ae-1357952fce52@huawei.com> <80b673a7-1097-c5fa-82c0-1056baa5309d@huawei.com> <7c05b08b-2edc-7f97-0175-898e9772673e@huawei.com> <668f819c8747104814245cd6faebdd9a@kernel.org> From: John Garry Message-ID: Date: Fri, 15 May 2020 12:50:06 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.1.2 MIME-Version: 1.0 In-Reply-To: <668f819c8747104814245cd6faebdd9a@kernel.org> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.47.1.24] X-ClientProxiedBy: lhreml709-chm.china.huawei.com (10.201.108.58) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Marc, > Absolutely. Life has got in the way, so let me page it back in... Great >> >> [PATCH 2/2] irqchip/gic-v3-its: Handle no overlap of non-managed irq >> affinity mask >> >> In selecting the target CPU for a non-managed interrupt, we may select >> a >> target CPU outside the requested affinity mask. >> >> This is because there may be no overlap of the ITS node mask and the >> requested CPU affinity mask. The requested affinity mask may be coming >> from userspace or some drivers which try to set irq affinity, see [0]. >> >> In this case, just ignore the ITS node cpumask. This is a deviation >> from >> what Thomas described. Having said that, I am not sure if the >> interrupt is ever bound to a node for us. >> >> [0] >> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/perf/hisilicon/hisi_uncore_pmu.c#n417 >> >> --- >> drivers/irqchip/irq-gic-v3-its.c | 4 ---- >> 1 file changed, 4 deletions(-) >> >> diff --git a/drivers/irqchip/irq-gic-v3-its.c >> b/drivers/irqchip/irq-gic-v3-its.c >> index 2b18feb..12d5d4b4 100644 >> --- a/drivers/irqchip/irq-gic-v3-its.c >> +++ b/drivers/irqchip/irq-gic-v3-its.c >> @@ -1584,10 +1584,6 @@ static int its_select_cpu(struct irq_data *d, >> cpumask_and(tmpmask, cpumask_of_node(node), aff_mask); >> cpumask_and(tmpmask, tmpmask, cpu_online_mask); >> >> - /* If that doesn't work, try the nodemask itself */ >> - if (cpumask_empty(tmpmask)) >> - cpumask_and(tmpmask, cpumask_of_node(node), cpu_online_mask); >> - >> cpu = cpumask_pick_least_loaded(d, tmpmask); >> if (cpu < nr_cpu_ids) >> goto out; > > I'm really not sure. Shouldn't we then drop the wider search on > cpu_inline_mask, because userspace could have given us something > that we cannot deal with? It's not just userspace. Some drivers call irq_set_affinity{_hint}}() also, with a non-overlapping affinity mask. We could just error these requests, but some drivers rely on this behavior. Consider the uncore driver I mentioned above, which WARNs when the affinity setting fails. So it tries to set the affinity with the cpumask of the cluster associated with the device, but with D06's ITS config, below, there may be no overlap. > > What you are advocating for is a strict adherence to the provided > mask, and it doesn't seem to be what other architectures are providing. > I consider the userspace-provided affinity as a hint more that anything > else, as in this case the kernel does know better (routing the interrupt > to a foreign node might be costly, or even impossible, see the TX1 > erratum). Right > > From what I remember of the earlier discussion, you saw an issue on > a system with two sockets and a single ITS, with the node mask limited > to the first socket. Is that correct? A bit more complicated: 2 sockets, 2 NUMA nodes per socket, and ITS config as follows: D06ES 1x ITS with proximity node #0 root@(none)$ dmesg | grep ITS [ 0.000000] SRAT: PXM 0 -> ITS 0 -> Node 0 D06CS 2x ITS with proximity node #0, #2 estuary:/$ dmesg | grep ITS [ 0.000000] SRAT: PXM 0 -> ITS 0 -> Node 0 [ 0.000000] SRAT: PXM 2 -> ITS 1 -> Node 2 It complicates things. We could add extra intelligence to record if an node has an ITS associated. In the case of that not being true, we would fallback on the requested affin only (for case of no overlap). It gets a bit more messy then. Thanks, John