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The man for cpuset doesn't seem to clearly list how to figure out which numbers map to which processing units. My current machine has two Intel Xeon E5645s, each of which has 6 cores and hyperthreading enabled, so I have 24 total processing units I can refer to with cpusets. My challenges are 1) determine which cpuset ID numbers map to which processor 2) determine which cpuset id numbers are paired (e.g. siblings on a core)

Are the numbers that lscpu outputs the same identifiers I should use to refer to cpu set processors? If so, it seems the numbers are alternated here, and this answers (1) with "evens are one processor, odds are the other processor", but I'm not sure if I'm reading it correctly. 

$ lscpu Architecture: x86_64 CPU op-mode(s): 32-bit, 64-bit Byte Order: Little Endian CPU(s): 24 On-line CPU(s) list: 0-23 Thread(s) per core: 2 Core(s) per socket: 6 Socket(s): 2 NUMA node(s): 2 Vendor ID: GenuineIntel CPU family: 6 Model: 44 Stepping: 2 CPU MHz: 2393.964 BogoMIPS: 4788.01 Virtualization: VT-x L1d cache: 32K L1i cache: 32K L2 cache: 256K L3 cache: 12288K NUMA node0 CPU(s): 0,2,4,6,8,10,12,14,16,18,20,22 NUMA node1 CPU(s): 1,3,5,7,9,11,13,15,17,19,21,23

lstopo from the hwloc package seems to show me the answer to (2), and if I'm reading the man page correctly the P#... bits are the identifier "used by the OS", which leads me to believe these are the ones I need to pass to cpu sets. So limiting a process to cpus 0 and 12 would be allowing use of two threads on the same core, while limiting it to cpus 0 and 2 would be two threads on two different cores. Does that seem correct? 

$ lstopo Machine (35GB) NUMANode L#0 (P#0 18GB) + Socket L#0 + L3 L#0 (12MB) L2 L#0 (256KB) + L1d L#0 (32KB) + L1i L#0 (32KB) + Core L#0 PU L#0 (P#0) PU L#1 (P#12) L2 L#1 (256KB) + L1d L#1 (32KB) + L1i L#1 (32KB) + Core L#1 PU L#2 (P#2) PU L#3 (P#14) L2 L#2 (256KB) + L1d L#2 (32KB) + L1i L#2 (32KB) + Core L#2 PU L#4 (P#4) PU L#5 (P#16) L2 L#3 (256KB) + L1d L#3 (32KB) + L1i L#3 (32KB) + Core L#3 PU L#6 (P#6) PU L#7 (P#18) L2 L#4 (256KB) + L1d L#4 (32KB) + L1i L#4 (32KB) + Core L#4 PU L#8 (P#8) PU L#9 (P#20) L2 L#5 (256KB) + L1d L#5 (32KB) + L1i L#5 (32KB) + Core L#5 PU L#10 (P#10) PU L#11 (P#22) NUMANode L#1 (P#1 18GB) + Socket L#1 + L3 L#1 (12MB) L2 L#6 (256KB) + L1d L#6 (32KB) + L1i L#6 (32KB) + Core L#6 PU L#12 (P#1) PU L#13 (P#13) L2 L#7 (256KB) + L1d L#7 (32KB) + L1i L#7 (32KB) + Core L#7 PU L#14 (P#3) PU L#15 (P#15) L2 L#8 (256KB) + L1d L#8 (32KB) + L1i L#8 (32KB) + Core L#8 PU L#16 (P#5) PU L#17 (P#17) L2 L#9 (256KB) + L1d L#9 (32KB) + L1i L#9 (32KB) + Core L#9 PU L#18 (P#7) PU L#19 (P#19) L2 L#10 (256KB) + L1d L#10 (32KB) + L1i L#10 (32KB) + Core L#10 PU L#20 (P#9) PU L#21 (P#21) L2 L#11 (256KB) + L1d L#11 (32KB) + L1i L#11 (32KB) + Core L#11 PU L#22 (P#11) PU L#23 (P#23) HostBridge L#0 PCIBridge PCI 14e4:163a Net L#0 "eth0" PCI 14e4:163a Net L#1 "eth1" PCIBridge PCI 102b:0532 PCI 8086:2921 Block L#2 "sda" PCI 8086:2926
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2 Answers 2

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use

cat /proc/cpuinfo

there you will get each hyperthread listed like this:

processor : 0 physical id : 0 core id : 1

"processor" stands for the "logical processor", what is presented to the operating system as a processor. If you have hyper threading switched on, you will see two "logical processors" per core. The "physical id" will be the processor that you can touch (you have two of them).

Here is a listing from my 1-processor 4-core system with hyperthreading:

# cat /proc/cpuinfo|egrep "processor|core id|physical id" processor : 0 physical id : 0 core id : 0 processor : 1 physical id : 0 core id : 1 processor : 2 physical id : 0 core id : 2 processor : 3 physical id : 0 core id : 3 processor : 4 physical id : 0 core id : 0 processor : 5 physical id : 0 core id : 1 processor : 6 physical id : 0 core id : 2 processor : 7 physical id : 0 core id : 3
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    Yes, but do you have any confirmation that these numbers are the ones used by cpu set....? Commented Nov 1, 2014 at 7:58
  • cpuset does not exist in my distribution (SUSE) which /proc/cpuinfo exists whereever there is a Linux kernel. I would not use cpuset. If you insist to, use sched_setaffinity to pin a process to a CPU, then you can use different programs to find out what CPU it is running on. Commented Nov 1, 2014 at 8:02
  • It's not that I insist, it's that my entire question is about how to figure out which IDs are correct for cpu set. Seems like you've answered the wrong question - I understand proc/cpuinfo and multiple other tools, but the complication is that I don't know how they relate to cpuset Commented Nov 1, 2014 at 8:04
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lstopo --cpuset

Will tell you what cpusets you should use to include each logical processor in the mask format.

You can convert that to the processor list format to check the processor numbers match.

Or if you are like me and are lazy you can do something like

taskset 0x00800000 grep -i Cpus_allowed /proc/self/status

And you'll get an output like

Cpus_allowed: 000,00800000 Cpus_allowed_list: 23

Which when I use lstopo --cpuset on my test machine matches

PU L#46 (P#23) cpuset=0x00800000

So you should use the number in (P#nn) when you are setting a cpuset using the list format.

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