physical cores - linux

[satish]

Dear Erman,

How could we identify the physical cores in a system when there are 2 sockets.When going to buy oracle licences,they have updates us to give the number of cores

Below shows 24

/u01/PROD/inst/apps/SSSEBSPR_ssstindcpodb02/logs/appl/conc/log > getconf _NPROCESSORS_ONLN 2>/dev/null || getconf NPROCESSORS_ONLN 2>/dev/null || echo 1
24

Below shows 6

/u01/PROD/inst/apps/SSSEBSPR_ssstindcpodb02/logs/appl/conc/log > grep '^core id' /proc/cpuinfo |sort -u|wc -l
6


What command will give us the number of cores when we have multiprocessor and more than 1 socket?

Thank you

[ErmanArslansOracleBlog]

Check /proc/cpuinfo

physical id there is the cpu.
core id there is the core.

you can derive the core count by checking the entries, which have the same physical id but different core id.
Check the distinct ones.. I mean if you have HT enabled, then you may see similar outputs for the same cores. So only take the distinct entries into consideration.

For example:

If you have only these entries below; it means you have 1 dual core cpu and that's it.

processor   : 0
physical id : 0
core id : 0

processor   : 1
physical id : 0
core id : 1

[satish]

Thanks erman.

We have quad core cpu

[oraprod@node1 ~]$ cat /proc/cpuinfo|grep -i 'core id'|sort|uniq
core id         : 0
core id         : 1
core id         : 2
core id         : 3

[oraprod@node1~]$ cat /proc/cpuinfo|grep -i 'physical id'|sort|uniq
physical id     : 0


In general,manual says load average or say run queue(r column in vmstat) should not exceed the number of cores consistently.In this case,if i have quad core cpu with HTT enabled,what will be the number of cores to consider...is it 4 or 8

Thank you

[ErmanArslansOracleBlog]

Yes.
4 is the critical load for you.
After 4 , your processes "may" start to slow down little by little, because they will be queued.

[ErmanArslansOracleBlog]

Oh sorry.
You have a 4 core cpu with HT enabled, then that number is 8 for you..

[ErmanArslansOracleBlog]

Still try to keep it at 7.. just in case.. Cause Hyperthreading is a method rather than a real processor or core , so it is good to keep a buffer for it.

[Sri]

Thanks for the update erman.

This is where my confusion lies. Is it 4 or 7?

As per your previous update,we should consider 7.pls correct me if i am wrong

Thank you

[Sri]

Missed your previous update...thanks for the clarification.This Information is useful to many of us