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: I feel puzzled at the function cpumask_of_node

Question or BUG Leizhen (ThunderTown) 2 participants 3 messages Jun 7, 2017 – Jun 15, 2017

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Leizhen (ThunderTown)

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When I executed numactl -H(print cpumask_of_node for each node), I got different result on X86 and ARM64. For each numa node, the former only displayed online CPUs, and the latter displayed all possible CPUs. Actually, all other ARCHs is the same to ARM64.

So, my question is: Which case(online or possible) should function cpumask_of_node be? Or there is no matter about it?

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Thanks!
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#1 lore raw

[CC linux-api]

Quoted 7 lines · Leizhen (ThunderTown)

When I executed numactl -H(print cpumask_of_node for each node), I got different result on X86 and ARM64. For each numa node, the former only displayed online CPUs, and the latter displayed all possible CPUs. Actually, all other ARCHs is the same to ARM64.

So, my question is: Which case(online or possible) should function cpumask_of_node be? Or there is no matter about it?

Unfortunatelly the documentation is quite unclear
What: /sys/devices/system/node/nodeX/cpumap
Date: October 2002
Contact: Linux Memory Management list <[email protected]>
Description:
The node's cpumap.

not really helpeful, is it? Semantically I _think_ printing online cpus makes more sense because it doesn't really make much sense to bind anything on offline nodes. Generic implementtion of cpumask_of_node indeed provides only online cpus. I haven't checked specific implementations of arch specific code but listing offline cpus sounds confusing to me.

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Michal Hocko
SUSE Labs

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Quoted 18 lines · Michal Hocko

[CC linux-api]

Quoted 7 lines · Leizhen (ThunderTown)

When I executed numactl -H(print cpumask_of_node for each node), I got different result on X86 and ARM64. For each numa node, the former only displayed online CPUs, and the latter displayed all possible CPUs. Actually, all other ARCHs is the same to ARM64.

So, my question is: Which case(online or possible) should function cpumask_of_node be? Or there is no matter about it?

Unfortunatelly the documentation is quite unclear
What: /sys/devices/system/node/nodeX/cpumap
Date: October 2002
Contact: Linux Memory Management list <[email protected]>
Description:
The node's cpumap.

Quoted 7 lines

not really helpeful, is it? Semantically I _think_ printing online cpus makes more sense because it doesn't really make much sense to bind anything on offline nodes. Generic implementtion of cpumask_of_node indeed provides only online cpus. I haven't checked specific implementations of arch specific code but listing offline cpus sounds confusing to me.

OK, thank you very much. So, how about we directly add "cpumask_and with cpu_online_mask", as below:

drivers/base/node.c +4 -2
index b10479c..199723d 100644
@@ -28,12 +28,14 @@ static struct bus_type node_subsys = {
 static ssize_t node_read_cpumap(struct device *dev, bool list, char *buf)
 {
        struct node *node_dev = to_node(dev);
-   const struct cpumask *mask = cpumask_of_node(node_dev->dev.id);
+ struct cpumask mask;
+
+ cpumask_and(&mask, cpumask_of_node(node_dev->dev.id), cpu_online_mask);
 
        /* 2008/04/07: buf currently PAGE_SIZE, need 9 chars per 32 bits. */
        BUILD_BUG_ON((NR_CPUS/32 * 9) > (PAGE_SIZE-1));
 
-   return cpumap_print_to_pagebuf(list, buf, mask);
+ return cpumap_print_to_pagebuf(list, buf, &mask);
 }
 
 static inline ssize_t node_read_cpumask(struct device *dev,
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Thanks!
BestRegards