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=-13.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 F28B2C55178 for ; Mon, 26 Oct 2020 23:53:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C43192151B for ; Mon, 26 Oct 2020 23:53:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603756414; bh=kyEewnVBVkaDGzRqY6v8My85Gla89CAOx9ljs28QbXs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=aIKrrQaaQB/CpVYk2slyjl256/6spHQfevNIe/8Y4b1+iyMMjSJFXJEKxfKzJA7Xm 0CW5/ri2c8wp2lTEbCoTRO7fzl/Kg8VXcq/DzrEi0ru24CL6uFZy06iPRloK8qKgj2 Y1fQ9F2j5RbXRrFr1pbI9rGnV7WZ3UGOts8TQU88= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2410107AbgJZXxc (ORCPT ); Mon, 26 Oct 2020 19:53:32 -0400 Received: from mail.kernel.org ([198.145.29.99]:56864 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2409953AbgJZXxF (ORCPT ); Mon, 26 Oct 2020 19:53:05 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EC1C120B1F; Mon, 26 Oct 2020 23:53:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603756384; bh=kyEewnVBVkaDGzRqY6v8My85Gla89CAOx9ljs28QbXs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=r4SxyUM79x7Fl3RG4Ierrt5uhK++uFDrA5AzMyFdTfc8w0FgWxp2j9+0qGMrcbiGy hYCIg3BE/TdJe09Kq4KhX6yJI4yyJD/Ike6LhTrb6t4uEYACZxAVtd8OA6dU267SFH nEn4d2Rrh+5oE3YMvdqOoSm2c8yXx3CPFx5AXEko= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Valentin Schneider , Sudeep Holla , Will Deacon , Sasha Levin , linux-arm-kernel@lists.infradead.org Subject: [PATCH AUTOSEL 5.8 048/132] arm64: topology: Stop using MPIDR for topology information Date: Mon, 26 Oct 2020 19:50:40 -0400 Message-Id: <20201026235205.1023962-48-sashal@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20201026235205.1023962-1-sashal@kernel.org> References: <20201026235205.1023962-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Valentin Schneider [ Upstream commit 3102bc0e6ac752cc5df896acb557d779af4d82a1 ] In the absence of ACPI or DT topology data, we fallback to haphazardly decoding *something* out of MPIDR. Sadly, the contents of that register are mostly unusable due to the implementation leniancy and things like Aff0 having to be capped to 15 (despite being encoded on 8 bits). Consider a simple system with a single package of 32 cores, all under the same LLC. We ought to be shoving them in the same core_sibling mask, but MPIDR is going to look like: | CPU | 0 | ... | 15 | 16 | ... | 31 | |------+---+-----+----+----+-----+----+ | Aff0 | 0 | ... | 15 | 0 | ... | 15 | | Aff1 | 0 | ... | 0 | 1 | ... | 1 | | Aff2 | 0 | ... | 0 | 0 | ... | 0 | Which will eventually yield core_sibling(0-15) == 0-15 core_sibling(16-31) == 16-31 NUMA woes ========= If we try to play games with this and set up NUMA boundaries within those groups of 16 cores via e.g. QEMU: # Node0: 0-9; Node1: 10-19 $ qemu-system-aarch64 \ -smp 20 -numa node,cpus=0-9,nodeid=0 -numa node,cpus=10-19,nodeid=1 The scheduler's MC domain (all CPUs with same LLC) is going to be built via arch_topology.c::cpu_coregroup_mask() In there we try to figure out a sensible mask out of the topology information we have. In short, here we'll pick the smallest of NUMA or core sibling mask. node_mask(CPU9) == 0-9 core_sibling(CPU9) == 0-15 MC mask for CPU9 will thus be 0-9, not a problem. node_mask(CPU10) == 10-19 core_sibling(CPU10) == 0-15 MC mask for CPU10 will thus be 10-19, not a problem. node_mask(CPU16) == 10-19 core_sibling(CPU16) == 16-19 MC mask for CPU16 will thus be 16-19... Uh oh. CPUs 16-19 are in two different unique MC spans, and the scheduler has no idea what to make of that. That triggers the WARN_ON() added by commit ccf74128d66c ("sched/topology: Assert non-NUMA topology masks don't (partially) overlap") Fixing MPIDR-derived topology ============================= We could try to come up with some cleverer scheme to figure out which of the available masks to pick, but really if one of those masks resulted from MPIDR then it should be discarded because it's bound to be bogus. I was hoping to give MPIDR a chance for SMT, to figure out which threads are in the same core using Aff1-3 as core ID, but Sudeep and Robin pointed out to me that there are systems out there where *all* cores have non-zero values in their higher affinity fields (e.g. RK3288 has "5" in all of its cores' MPIDR.Aff1), which would expose a bogus core ID to userspace. Stop using MPIDR for topology information. When no other source of topology information is available, mark each CPU as its own core and its NUMA node as its LLC domain. Signed-off-by: Valentin Schneider Reviewed-by: Sudeep Holla Link: https://lore.kernel.org/r/20200829130016.26106-1-valentin.schneider@arm.com Signed-off-by: Will Deacon Signed-off-by: Sasha Levin --- arch/arm64/kernel/topology.c | 32 +++++++++++++++++--------------- 1 file changed, 17 insertions(+), 15 deletions(-) diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c index 0801a0f3c156a..ff1dd1dbfe641 100644 --- a/arch/arm64/kernel/topology.c +++ b/arch/arm64/kernel/topology.c @@ -36,21 +36,23 @@ void store_cpu_topology(unsigned int cpuid) if (mpidr & MPIDR_UP_BITMASK) return; - /* Create cpu topology mapping based on MPIDR. */ - if (mpidr & MPIDR_MT_BITMASK) { - /* Multiprocessor system : Multi-threads per core */ - cpuid_topo->thread_id = MPIDR_AFFINITY_LEVEL(mpidr, 0); - cpuid_topo->core_id = MPIDR_AFFINITY_LEVEL(mpidr, 1); - cpuid_topo->package_id = MPIDR_AFFINITY_LEVEL(mpidr, 2) | - MPIDR_AFFINITY_LEVEL(mpidr, 3) << 8; - } else { - /* Multiprocessor system : Single-thread per core */ - cpuid_topo->thread_id = -1; - cpuid_topo->core_id = MPIDR_AFFINITY_LEVEL(mpidr, 0); - cpuid_topo->package_id = MPIDR_AFFINITY_LEVEL(mpidr, 1) | - MPIDR_AFFINITY_LEVEL(mpidr, 2) << 8 | - MPIDR_AFFINITY_LEVEL(mpidr, 3) << 16; - } + /* + * This would be the place to create cpu topology based on MPIDR. + * + * However, it cannot be trusted to depict the actual topology; some + * pieces of the architecture enforce an artificial cap on Aff0 values + * (e.g. GICv3's ICC_SGI1R_EL1 limits it to 15), leading to an + * artificial cycling of Aff1, Aff2 and Aff3 values. IOW, these end up + * having absolutely no relationship to the actual underlying system + * topology, and cannot be reasonably used as core / package ID. + * + * If the MT bit is set, Aff0 *could* be used to define a thread ID, but + * we still wouldn't be able to obtain a sane core ID. This means we + * need to entirely ignore MPIDR for any topology deduction. + */ + cpuid_topo->thread_id = -1; + cpuid_topo->core_id = cpuid; + cpuid_topo->package_id = cpu_to_node(cpuid); pr_debug("CPU%u: cluster %d core %d thread %d mpidr %#016llx\n", cpuid, cpuid_topo->package_id, cpuid_topo->core_id, -- 2.25.1