From patchwork Sat Jan 21 04:24:36 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yury Norov X-Patchwork-Id: 13110841 X-Patchwork-Delegate: kuba@kernel.org 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DFE6BC5320B for ; Sat, 21 Jan 2023 04:25:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229672AbjAUEZV (ORCPT ); Fri, 20 Jan 2023 23:25:21 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36480 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229568AbjAUEZJ (ORCPT ); Fri, 20 Jan 2023 23:25:09 -0500 Received: from mail-qt1-x829.google.com (mail-qt1-x829.google.com [IPv6:2607:f8b0:4864:20::829]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 70723530EC; Fri, 20 Jan 2023 20:24:53 -0800 (PST) Received: by mail-qt1-x829.google.com with SMTP id g16so3765838qtu.2; Fri, 20 Jan 2023 20:24:53 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=qwRl6AriAxtLsQshG0WLT8xXpSJi+NGIVxpWZYX/6II=; b=oYxzuFmr5pVt01gJibPdD5ns77LWVJeQmmVcsoPATQ4AhkNE8Da5wsu9Mc1wJLeNaB tehkdeWQw8aXAeGragVTrfuwq647RKKSq23gNAuq9fjHG5+mwpwbdicJcnlrSaljEfQr Eb4bFX6NvVp0r5sOxhE2t/7kgma9WzMeWKopGbGj4cFeEf3SghA9EFKoNP2F8ewXDmpg 1GJMDoD0tN/M476NAiSuwmkMZjRnvs29wvpAoqtHYdA4dhfCJDtFiNT4jD3KDxwhJWJy 7aVDQmCmdhwT0P+5kyStCHbeHIKIm0dZSkrbfczaE/6i5VUbDGixfB8lbev7Cga34Dh4 WNOQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=qwRl6AriAxtLsQshG0WLT8xXpSJi+NGIVxpWZYX/6II=; b=wVG6Gd/rAGHQc2rlv9wYu0+LBdmUgtcntNe1rssNUWfZw5j2OSNzHu/4eEiqJ2uNWE 6RIGnjH147H+VLLT2/YiWJTrT8+wWgGb2Ki+n8IvUpIPxZdDGaou6jyOpuoDK5X2cDhk zfJYB53CgMlRqEAp1ggjbDvtI3HvJDCX9vegzal9dTvROZAPt+82jS9AFHZ4bX8grCH9 jLliBqUQT/UpADEPHWtxJBfiBZ3OaRhrTlgPPN4CP08xqKzjtJOD9LEdo5At0Ap1jkVd W+CZLY3VXAG9EY6IQtNaCEPXpVPajuiLcYgDyWZCNMBczHXd+m9+Q1kHsCZ3B4Ib2I8f E3Rg== X-Gm-Message-State: AFqh2kolEj+i1bDZ8BECtUVoBZpNOYxNwwyWHOGyDjE2h+Xl4U2XD8M+ Z/btl2BBENcohzdoB5giy0VUGH9b2tE= X-Google-Smtp-Source: AMrXdXuIb83rZuSdHzA4rxpr75oAXNzqP23zVDgdCNSGS7ZxV26QSDHnFK2M21j5vg9ZIdQWGnLVzw== X-Received: by 2002:ac8:6a0e:0:b0:3ab:7928:526c with SMTP id t14-20020ac86a0e000000b003ab7928526cmr23006426qtr.17.1674275092061; Fri, 20 Jan 2023 20:24:52 -0800 (PST) Received: from localhost (50-242-44-45-static.hfc.comcastbusiness.net. [50.242.44.45]) by smtp.gmail.com with ESMTPSA id ga15-20020a05622a590f00b003b6325dfc4esm8255304qtb.67.2023.01.20.20.24.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 20 Jan 2023 20:24:51 -0800 (PST) From: Yury Norov To: linux-kernel@vger.kernel.org, "David S. Miller" , Andy Shevchenko , Barry Song , Ben Segall , Dietmar Eggemann , Gal Pressman , Greg Kroah-Hartman , Haniel Bristot de Oliveira , Heiko Carstens , Ingo Molnar , Jacob Keller , Jakub Kicinski , Jason Gunthorpe , Jesse Brandeburg , Jonathan Cameron , Juri Lelli , Leon Romanovsky , Linus Torvalds , Mel Gorman , Peter Lafreniere , Peter Zijlstra , Rasmus Villemoes , Saeed Mahameed , Steven Rostedt , Tariq Toukan , Tariq Toukan , Tony Luck , Valentin Schneider , Vincent Guittot Cc: Yury Norov , linux-crypto@vger.kernel.org, netdev@vger.kernel.org, linux-rdma@vger.kernel.org Subject: [PATCH 9/9] lib/cpumask: update comment for cpumask_local_spread() Date: Fri, 20 Jan 2023 20:24:36 -0800 Message-Id: <20230121042436.2661843-10-yury.norov@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230121042436.2661843-1-yury.norov@gmail.com> References: <20230121042436.2661843-1-yury.norov@gmail.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Now that we have an iterator-based alternative for a very common case of using cpumask_local_spread for all cpus in a row, it's worth to mention that in comment to cpumask_local_spread(). Signed-off-by: Yury Norov Reviewed-by: Valentin Schneider Reviewed-by: Tariq Toukan --- lib/cpumask.c | 26 ++++++++++++++++++++++---- 1 file changed, 22 insertions(+), 4 deletions(-) diff --git a/lib/cpumask.c b/lib/cpumask.c index 10aa15715c0d..98291b07c756 100644 --- a/lib/cpumask.c +++ b/lib/cpumask.c @@ -114,11 +114,29 @@ void __init free_bootmem_cpumask_var(cpumask_var_t mask) * @i: index number * @node: local numa_node * - * This function selects an online CPU according to a numa aware policy; - * local cpus are returned first, followed by non-local ones, then it - * wraps around. + * Returns online CPU according to a numa aware policy; local cpus are returned + * first, followed by non-local ones, then it wraps around. * - * It's not very efficient, but useful for setup. + * For those who wants to enumerate all CPUs based on their NUMA distances, + * i.e. call this function in a loop, like: + * + * for (i = 0; i < num_online_cpus(); i++) { + * cpu = cpumask_local_spread(i, node); + * do_something(cpu); + * } + * + * There's a better alternative based on for_each()-like iterators: + * + * for_each_numa_hop_mask(mask, node) { + * for_each_cpu_andnot(cpu, mask, prev) + * do_something(cpu); + * prev = mask; + * } + * + * It's simpler and more verbose than above. Complexity of iterator-based + * enumeration is O(sched_domains_numa_levels * nr_cpu_ids), while + * cpumask_local_spread() when called for each cpu is + * O(sched_domains_numa_levels * nr_cpu_ids * log(nr_cpu_ids)). */ unsigned int cpumask_local_spread(unsigned int i, int node) {