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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 EFB18C43461 for ; Mon, 17 May 2021 18:50:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D12C061002 for ; Mon, 17 May 2021 18:50:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237319AbhEQSwD (ORCPT ); Mon, 17 May 2021 14:52:03 -0400 Received: from foss.arm.com ([217.140.110.172]:60350 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234049AbhEQSwC (ORCPT ); Mon, 17 May 2021 14:52:02 -0400 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 28FB331B; Mon, 17 May 2021 11:50:45 -0700 (PDT) Received: from [10.57.66.179] (unknown [10.57.66.179]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 60CBF3F73D; Mon, 17 May 2021 11:50:41 -0700 (PDT) Subject: Re: [PATCH tip:irq/core v1] genirq: remove auto-set of the mask when setting the hint To: Thomas Gleixner , Nitesh Lal , Jesse Brandeburg , "frederic@kernel.org" , "juri.lelli@redhat.com" , Marcelo Tosatti Cc: Ingo Molnar , linux-kernel@vger.kernel.org, intel-wired-lan@lists.osuosl.org, jbrandeb@kernel.org, Alex Belits , "linux-api@vger.kernel.org" , "bhelgaas@google.com" , "linux-pci@vger.kernel.org" , "rostedt@goodmis.org" , "peterz@infradead.org" , "davem@davemloft.net" , "akpm@linux-foundation.org" , "sfr@canb.auug.org.au" , "stephen@networkplumber.org" , "rppt@linux.vnet.ibm.com" , "jinyuqi@huawei.com" , "zhangshaokun@hisilicon.com" , netdev@vger.kernel.org, chris.friesen@windriver.com, Marc Zyngier References: <20210501021832.743094-1-jesse.brandeburg@intel.com> <16d8ca67-30c6-bb4b-8946-79de8629156e@arm.com> <20210504092340.00006c61@intel.com> <87sg2lz0zz.ffs@nanos.tec.linutronix.de> From: Robin Murphy Message-ID: Date: Mon, 17 May 2021 19:50:35 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <87sg2lz0zz.ffs@nanos.tec.linutronix.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-05-17 19:08, Thomas Gleixner wrote: > On Mon, May 17 2021 at 18:26, Robin Murphy wrote: >> On 2021-05-17 17:57, Nitesh Lal wrote: >> I'm not implying that there isn't a bug, or that this code ever made >> sense in the first place, just that fixing it will unfortunately be a >> bit more involved than a simple revert. This patch as-is *will* subtly >> break at least the system PMU drivers currently using > > s/using/abusing/ > >> irq_set_affinity_hint() - those I know require the IRQ affinity to >> follow whichever CPU the PMU context is bound to, in order to meet perf >> core's assumptions about mutual exclusion. > > Which driver is that? Right now, any driver which wants to control an IRQ's affinity and also build as a module, for one thing. I'm familiar with drivers/perf/ where a basic pattern has been widely copied; some of the callers in other subsystems appear to *expect* it to set the underlying affinity as well, but whether any of those added within the last 6 years represent a functional dependency rather than just a performance concern I don't know. Robin.