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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Sep 02, 2019 at 01:46:51PM +0800, Yunsheng Lin wrote: > On 2019/9/1 0:12, Peter Zijlstra wrote: > > 1) because even it is not set, the device really does belong to a node. > > It is impossible a device will have magic uniform access to memory when > > CPUs cannot. > > So it means dev_to_node() will return either NUMA_NO_NODE or a > valid node id? NUMA_NO_NODE := -1, which is not a valid node number. It is also, like I said, not a valid device location on a NUMA system. Just because ACPI/BIOS is shit, doesn't mean the device doesn't have a node association. It just means we don't know and might have to guess. > > 2) is already true today, cpumask_of_node() requires a valid node_id. > > Ok, most of the user does check node_id before calling > cpumask_of_node(), but does a little different type of checking: > > 1) some does " < 0" check; > 2) some does "== NUMA_NO_NODE" check; > 3) some does ">= MAX_NUMNODES" check; > 4) some does "< 0 || >= MAX_NUMNODES || !node_online(node)" check. The one true way is: '(unsigned)node_id >= nr_node_ids' > > 3) is just wrong and increases overhead for everyone. > > Ok, cpumask_of_node() is also used in some critical path such > as scheduling, which may not need those checking, the overhead > is unnecessary. > > But for non-critical path such as setup or configuration path, > it better to have consistent checking, and also simplify the > user code that calls cpumask_of_node(). > > Do you think it is worth the trouble to add a new function > such as cpumask_of_node_check(maybe some other name) to do > consistent checking? > > Or caller just simply check if dev_to_node()'s return value is > NUMA_NO_NODE before calling cpumask_of_node()? It is not a matter of convenience. The function is called cpumask_of_node(), when node < 0 || node >= nr_node_ids, it is not a valid node, therefore the function shouldn't return anything except an error. Also note that the CONFIG_DEBUG_PER_CPU_MAPS version of cpumask_of_node() already does this (although it wants the below fix). --- diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c index e6dad600614c..5f49c10201c7 100644 --- a/arch/x86/mm/numa.c +++ b/arch/x86/mm/numa.c @@ -861,7 +861,7 @@ void numa_remove_cpu(int cpu) */ const struct cpumask *cpumask_of_node(int node) { - if (node >= nr_node_ids) { + if ((unsigned)node >= nr_node_ids) { printk(KERN_WARNING "cpumask_of_node(%d): node > nr_node_ids(%u)\n", node, nr_node_ids); _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel