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[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: linux-rdma@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) {