On Thu, Nov 19, 2020 at 01:13:20PM +0000, Will Deacon wrote:

Sure, but I was talking about what userspace sees, and I don't think it ever
sees CPUs that have been hotplugged off, right? That is, sched_getaffinity()
masks its result with the active_mask.

# for i in /sys/devices/system/cpu/cpu*/online; do echo -n $i ":"; cat $i; done
/sys/devices/system/cpu/cpu1/online :0
/sys/devices/system/cpu/cpu2/online :1
/sys/devices/system/cpu/cpu3/online :1
/sys/devices/system/cpu/cpu4/online :1
/sys/devices/system/cpu/cpu5/online :1
/sys/devices/system/cpu/cpu6/online :1
/sys/devices/system/cpu/cpu7/online :1

# grep Cpus_allowed /proc/self/status
Cpus_allowed:   ff
Cpus_allowed_list:      0-7


:-)

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