From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B565C606A319 for ; Tue, 20 Oct 2026 01:15:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=lists.infradead.org header.i=@lists.infradead.org header.a=rsa-sha256 header.s=bombadil.20210309 header.b=qIi+nhl3; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=aUXvDw36 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:Reply-To:List-Subscribe: List-Help:List-Post:List-Archive:List-Unsubscribe:List-Id:Date: Content-Transfer-Encoding:Content-Type:References:In-Reply-To:To:Subject:From :Message-ID:Cc:MIME-Version:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=RS8J52qtbt5ODgVr495qoddqVVw0Sm8CPmkFBES4OcM=; b=qIi+nhl3/zyVSq02g5ERVLQMbZ EwQmIEHngRTIxgHUrWko1M+9VVHyAjMjZ2vyUs+SLswe2FYmKVyesXr3TSaneB8N3+128vb/zasBv uFJOC3vXl1lbRgBFenK8QXGR+eFWr6Na/EaAtbgKEgMeuFWjkNmbqHlR1VUikT8DqZNgTjL9rvVXl hj6UNHayAGT+sf5+REi/BtNdw6MSXIPsy7inbJn7oCEIojruwgyHxpd05RmrIXEsqD9QYCodXw/t0 3Mbjz5qUMWTQ+G2F6PoluC2B4StSx3vi1ZPtAIEXnTN1LdHR5Lt09H6YXjpipe17Gy4UKWRvP4NLQ 5eiUAkkA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xIySM-00000008bMi-01Dn; Tue, 20 Oct 2026 01:15:58 +0000 Received: from tor.source.kernel.org ([2600:3c04:e001:324:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1xIySK-00000008bLC-24in for kexec@lists.infradead.org; Tue, 20 Oct 2026 01:15:56 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id E64FF605ED; Tue, 20 Oct 2026 01:15:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 723901F000C4; Tue, 20 Oct 2026 01:15:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792458955; bh=RS8J52qtbt5ODgVr495qoddqVVw0Sm8CPmkFBES4OcM=; h=From:Subject:Reply-To:To:In-Reply-To:References:Date; b=aUXvDw36QhplmI8qFeLnXKIdX6gL3p4NdKWC8GS8Y02s2ndaREO9pV2Dq4e3u4iLk h0oRGFG6QhqqksthfbVNULciUZZIOxjYhlwltRPReaSrgSL1A5/+PJqXeD/JaYHP/0 tpWcCJDjs8JLlexNrlgfm43loamFm6Rt20XnIswao8iLMI1gVg8Ch1SfYbVV8DeiO1 Un8xdl/3ug1IQ3tkaf6fM1KhikU+SdFagUuMV9GH+Lr/GzAmWqTrXdLgLldpG2yTka GLkNsOLdrNaSADNzsxbroy1IImuqGPLLLaS55qj2RfoOE/DLJUIgDhdBGGxIJrYLeE xm0IBLQHC3ixA== Message-ID: From: sashiko-bot@kernel.org Subject: Re: [PATCH v2 5/8] sched/topology: Avoid redundant O(N^3) group capacity walks and unused allocations in build_sched_domains() To: "Pasha Tatashin" , kees@kernel.org, rppt@kernel.org, juri.lelli@redhat.com, nik.borisov@suse.com, tglx@kernel.org, vschneid@redhat.com, kprateek.nayak@amd.com, vincent.guittot@linaro.org, bp@alien8.de, jpoimboe@kernel.org, tony.luck@intel.com, david@kernel.org, mingo@redhat.com, akpm@linux-foundation.org, seanjc@google.com, ljs@kernel.org, zhangguopeng@kylinos.cn, dietmar.eggemann@arm.com, mhocko@suse.com, vinicius.gomes@intel.com, vbabka@kernel.org, peterz@infradead.org, surenb@google.com, hpa@zytor.com, x86@kernel.org, dmatlack@google.com, tim.c.chen@linux.intel.com, kexec@lists.infradead.org, pratyush@kernel.org, dave.hansen@linux.intel.com, rostedt@goodmis.org, gmonaco@redhat.com, jgross@suse.com, mgorman@suse.de, graf@amazon.com, liam@infradead.org, ridong.chen@linux.dev, blum@kernel.org, longman@redhat.com, bsegall@google.com In-Reply-To: <20261019011446.834487-6-pasha.tatashin@soleen.com> References: <20261019011446.834487-1-pasha.tatashin@soleen.com> <20261019011446.834487-6-pasha.tatashin@soleen.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Tue, 20 Oct 2026 01:15:53 +0000 X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: sashiko-reviews@lists.linux.dev Sender: "kexec" X-Spam-Status: No, score=-11.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 X-Archived-By: > During sequential CPU hotplug on large systems, build_sched_domains() is > invoked for every CPU offline and online step. Two bottlenecks in the > domain construction path scale poorly with CPU count: >=20 > 1. On non-overlapping topology levels, all CPUs sharing a domain span > share the same circular ring of sched_group instances, and on > overlapping NUMA levels, groups with identical spans share > sched_group_capacity (sgc). However, init_sched_groups_capacity() > walks the entire group ring for every CPU in the domain and repeatedly > recomputes group_weight, cores (walking the group cpumask and clearing > cpu_smt_mask), and asym_prefer_cpu (O(N^3) bitmap operations per > hotplug step). Similarly, init_overlap_sched_group() recomputes > build_balance_mask() and cpumask_weight(sg_span) even when the shared > sgc was already initialized. >=20 > [ ... ] > Total: 7.66 s -> 5.29 s (-30.9%) > build_sched_domains() (cpu511 offline / online): > 11.69 ms -> 5.61 ms (-52.0%) / 12.24 ms -> 5.84 ms (-52.3%) >=20 > Signed-off-by: Pasha Tatashin Sashiko has reviewed this patch and found no issues. --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20261019011446.8344= 87-1-pasha.tatashin@soleen.com?part=3D5