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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Andy Shevchenko , Rasmus Villemoes , Ingo Molnar , Peter Zijlstra , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Mel Gorman , Greg Kroah-Hartman , Heiko Carstens , Tony Luck , Jonathan Cameron , Gal Pressman , Tariq Toukan , Jesse Brandeburg Subject: Re: [PATCH v4 5/7] sched/topology: Introduce sched_numa_hop_mask() In-Reply-To: References: <20220923132527.1001870-1-vschneid@redhat.com> <20220923155542.1212814-4-vschneid@redhat.com> Date: Tue, 27 Sep 2022 17:45:15 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain X-Spam-Status: No, score=-2.9 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_LOW, SPF_HELO_NONE,SPF_NONE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25/09/22 11:05, Yury Norov wrote: > On Fri, Sep 23, 2022 at 04:55:40PM +0100, Valentin Schneider wrote: >> +const struct cpumask *sched_numa_hop_mask(int node, int hops) >> +{ >> + struct cpumask ***masks = rcu_dereference(sched_domains_numa_masks); >> + >> + if (node == NUMA_NO_NODE && !hops) >> + return cpu_online_mask; >> + >> + if (node >= nr_node_ids || hops >= sched_domains_numa_levels) >> + return ERR_PTR(-EINVAL); > > This looks like a sanity check. If so, it should go before the snippet > above, so that client code would behave consistently. > nr_node_ids is unsigned, so -1 >= nr_node_ids is true. >> + >> + if (!masks) >> + return NULL; > > In (node == NUMA_NO_NODE && !hops) case you return online cpus. Here > you return NULL just to convert it to cpu_online_mask in the caller. > This looks inconsistent. So, together with the above comment, this > makes me feel that you'd do it like this: > > const struct cpumask *sched_numa_hop_mask(int node, int hops) > { > struct cpumask ***masks; > > if (node >= nr_node_ids || hops >= sched_domains_numa_levels) > { > #ifdef CONFIG_SCHED_DEBUG > pr_err(...); > #endif > return ERR_PTR(-EINVAL); > } > > if (node == NUMA_NO_NODE && !hops) > return cpu_online_mask; /* or NULL */ > > masks = rcu_dereference(sched_domains_numa_masks); > if (!masks) > return cpu_online_mask; /* or NULL */ > > return masks[hops][node]; > } If we're being pedantic, sched_numa_hop_mask() shouldn't return cpu_online_mask in those cases, but that was the least horrible option I found to get something sensible for the NUMA_NO_NODE / !CONFIG_NUMA case. I might be able to better handle this with your suggestion of having a mask iterator.