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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 82902C43334 for ; Fri, 8 Jul 2022 08:06:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc: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=Up5nAtemFSs6P0OP2c4aigcyObbneqA1UbE2Ko1jTHY=; b=FFeqHpABKC+gDL rtwaxovsTtdwClarzYuFZ9DjWo6ziqEp+jMZlmpQr/ecfCkY0LD3tiCW8w+1s4iMZriHYitydBhuT 54JhRAAtkEdNly3SGaSbpiVqd1krxuKdfGIgykeV/ykhFGqQAmxdo+viBjn/LGj8/b7c4w/QlEwZM Xc4pmwijHWYXqoIDe9ECsKv2k70zDUNpR+4Bul/8SadrBMH06oH2A1OMxpp3ZIMWYtJ+l01q/XxkP KFa7T7jLUXdd+d9A5JeaVozhXIjcGzC7dxX0flPgoMlx5eM3IRKFbPu0gnbkG4zoSan/tDnL7o1KQ 4bhAXo0ZdA5CocHsfqbA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1o9izu-002MeV-MW; Fri, 08 Jul 2022 08:05:58 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1o9izd-002MXH-U9; Fri, 08 Jul 2022 08:05:44 +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 BD9CE1063; Fri, 8 Jul 2022 01:05:38 -0700 (PDT) Received: from bogus (unknown [10.57.39.193]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 989E93F792; Fri, 8 Jul 2022 01:05:35 -0700 (PDT) Date: Fri, 8 Jul 2022 09:04:24 +0100 From: Sudeep Holla To: Darren Hart Cc: linux-kernel@vger.kernel.org, Greg Kroah-Hartman , conor.dooley@microchip.com, valentina.fernandezalanis@microchip.com, Vincent Guittot , Dietmar Eggemann , Qing Wang , Rob Herring , "Rafael J . Wysocki" , Ionela Voinescu , Pierre Gondois , Sudeep Holla , linux-arm-kernel@lists.infradead.org, linux-riscv@lists.infradead.org Subject: Re: [PATCH v6 17/21] arch_topology: Limit span of cpu_clustergroup_mask() Message-ID: <20220708080424.22x2bgcbggb6skua@bogus> References: <20220704101605.1318280-1-sudeep.holla@arm.com> <20220704101605.1318280-18-sudeep.holla@arm.com> 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-20220708_010542_102268_12DDC589 X-CRM114-Status: GOOD ( 28.93 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org Hi Darren, I will let Ionela or Dietmar cover some of the scheduler aspects as I don't have much knowledge in that area. On Thu, Jul 07, 2022 at 05:10:19PM -0700, Darren Hart wrote: > On Mon, Jul 04, 2022 at 11:16:01AM +0100, Sudeep Holla wrote: > > From: Ionela Voinescu > > Hi Sudeep and Ionela, > > > > > Currently the cluster identifier is not set on DT based platforms. > > The reset or default value is -1 for all the CPUs. Once we assign the > > cluster identifier values correctly, the cluster_sibling mask will be > > populated and returned by cpu_clustergroup_mask() to contribute in the > > creation of the CLS scheduling domain level, if SCHED_CLUSTER is > > enabled. > > > > To avoid topologies that will result in questionable or incorrect > > scheduling domains, impose restrictions regarding the span of clusters, > > Can you provide a specific example of a valid topology that results in > the wrong thing currently? > As a simple example, Juno with 2 clusters and L2 for each cluster. IIUC MC is preferred instead of CLS and both MC and CLS domains are exact match. > > > > While previously the scheduling domain builder code would have removed MC > > as redundant and kept CLS if SCHED_CLUSTER was enabled and the > > cpu_coregroup_mask() and cpu_clustergroup_mask() spanned the same CPUs, > > now CLS will be removed and MC kept. > > > > This is not desireable for all systems, particular those which don't > have an L3 but do share other resources - such as the snoop filter in > the case of the Ampere Altra. > > While not universally supported, we agreed in the discussion on the > above patch to allow systems to define clusters independently from the > L3 as an LLC since this is also independently defined in PPTT. > > Going back to my first comment - does this fix an existing system with a > valid topology? Yes as mentioned above Juno. > It's not clear to me what that would look like. The Ampere Altra presents > a cluster level in PPTT because that is the desireable topology for the > system. Absolutely wrong reason. It should present because the hardware is so, not because some OSPM desires something in someway. Sorry that's not how DT/ACPI is designed for. If 2 different OSPM desires different things, then one ACPI will not be sufficient. > If it's not desirable for another system to have the cluster topology - > shouldn't it not present that layer to the kernel in the first place? Absolutely 100% yes, it must present it if the hardware is designed so. No if or but. -- Regards, Sudeep _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv