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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 277D3C2BA2B for ; Thu, 9 Apr 2020 10:32:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 060BE20757 for ; Thu, 9 Apr 2020 10:32:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726689AbgDIKcW (ORCPT ); Thu, 9 Apr 2020 06:32:22 -0400 Received: from foss.arm.com ([217.140.110.172]:48316 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725970AbgDIKcW (ORCPT ); Thu, 9 Apr 2020 06:32:22 -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 312DF31B; Thu, 9 Apr 2020 03:32:22 -0700 (PDT) Received: from e113632-lin (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DE0FD3F73D; Thu, 9 Apr 2020 03:32:18 -0700 (PDT) References: <855831b59e1b3774b11c3e33050eac4cc4639f06.1583332765.git.vpillai@digitalocean.com> <20200401114215.36640-1-cj.chengjian@huawei.com> <20200409095941.GA25948@bogus> User-agent: mu4e 0.9.17; emacs 26.3 From: Valentin Schneider To: Sudeep Holla Cc: Cheng Jian , vpillai@digitalocean.com, aaron.lwe@gmail.com, aubrey.intel@gmail.com, aubrey.li@linux.intel.com, fweisbec@gmail.com, jdesfossez@digitalocean.com, joel@joelfernandes.org, joelaf@google.com, keescook@chromium.org, kerrnel@google.com, linux-kernel@vger.kernel.org, mgorman@techsingularity.net, mingo@kernel.org, naravamudan@digitalocean.com, pauld@redhat.com, pawan.kumar.gupta@linux.intel.com, pbonzini@redhat.com, peterz@infradead.org, pjt@google.com, tglx@linutronix.de, tim.c.chen@linux.intel.com, torvalds@linux-foundation.org, xiexiuqi@huawei.com, huawei.libin@huawei.com, w.f@huawei.com, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] sched/arm64: store cpu topology before notify_cpu_starting In-reply-to: <20200409095941.GA25948@bogus> Date: Thu, 09 Apr 2020 11:32:12 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/04/20 10:59, Sudeep Holla wrote: > On Wed, Apr 01, 2020 at 02:23:33PM +0100, Valentin Schneider wrote: >> >> (+LAKML, +Sudeep) >> > > Thanks Valentin. > >> On Wed, Apr 01 2020, Cheng Jian wrote: >> > when SCHED_CORE enabled, sched_cpu_starting() uses thread_sibling as >> > SMT_MASK to initialize rq->core, but only after store_cpu_topology(), >> > the thread_sibling is ready for use. >> > >> > notify_cpu_starting() >> > -> sched_cpu_starting() # use thread_sibling >> > >> > store_cpu_topology(cpu) >> > -> update_siblings_masks # set thread_sibling >> > >> > Fix this by doing notify_cpu_starting later, just like x86 do. >> > >> >> I haven't been following the sched core stuff closely; can't this >> rq->core assignment be done in sched_cpu_activate() instead? We already >> look at the cpu_smt_mask() in there, and it is valid (we go through the >> entirety of secondary_start_kernel() before getting anywhere near >> CPUHP_AP_ACTIVE). >> > > I too came to same conclusion. Did you see any issues ? Or is it > just code inspection in parity with x86 ? > With mainline this isn't a problem; with the core scheduling stuff there is an expectation that we can use the SMT masks in sched_cpu_starting(). >> I don't think this breaks anything, but without this dependency in >> sched_cpu_starting() then there isn't really a reason for this move. >> > > Based on the commit message, had a quick look at x86 code and I agree > this shouldn't break anything. However the commit message does make > complete sense to me, especially reference to sched_cpu_starting > while smt_masks are accessed in sched_cpu_activate. Or am I missing > to understand something here ? As stated above, it's not a problem for mainline, and AIUI we can change the core scheduling bits to only use the SMT mask in sched_cpu_activate() instead, therefore not requiring any change in the arch code. I'm not aware of any written rule that the topology masks should be usable from a given hotplug state upwards, only that right now we need them in sched_cpu_(de)activate() for SMT scheduling - and that is already working fine. So really this should be considering as a simple neutral cleanup; I don't really have any opinion on picking it up or not.