What do you do with NUMA?

[syzygy]

You need to detect HT and it is quite trivial.

[mcostalba]

You need to detect HT and it is quite trivial.

Ok, care to provide some working code or for you was just enough to make me smile?

[mar]

Ok, care to provide some working code or for you was just enough to make me smile?

it's bit 28 in edx (feature bits) in cpuid after eax=1

[mcostalba]

Ok, care to provide some working code or for you was just enough to make me smile?

it's bit 28 in edx (feature bits) in cpuid after eax=1

Is not so simple:

https://software.intel.com/en-us/forums ... pic/294575
http://wiki.osdev.org/Detecting_CPU_Topology_(80x86)
http://stackoverflow.com/questions/7274 ... ed-core-id

[mcostalba]

Is not so simple:

I explain better, our aim is to set the thread affinity to different physical cores, so I need to know if CPUX is on a different core than CPUY

[mar]

Is not so simple:

I explain better, our aim is to set the thread affinity to different physical cores, so I need to know if CPUX is on a different core than CPUY

I see, I thought you only need to detect HT.

Aren't the logical cores interleaved? Like each two logical cores are 1 physical (at least affinity on Windows seems to work this way, also mentioned in one othe links you sent)
This assumption might not hold in the future though...

[syzygy]

You need to detect HT and it is quite trivial.

Ok, care to provide some working code or for you was just enough to make me smile?

Thanks for biting. The numa patch already does it.

[mcostalba]

https://groups.google.com/forum/?fromgr ... FG7cChRxu0

[bob]

Ok, care to provide some working code or for you was just enough to make me smile?

it's bit 28 in edx (feature bits) in cpuid after eax=1

Is not so simple:

https://software.intel.com/en-us/forums ... pic/294575
http://wiki.osdev.org/Detecting_CPU_Topology_(80x86)
http://stackoverflow.com/questions/7274 ... ed-core-id

I side with Marco here. There are TWO issues:

(1) is hyper threading in use? This is trivial with CPUID

(2) which processor numbers share a physical core. This is NOT so trivial as it has changed multiple times over the past 10 years. I spent a lot of time on this and finally said "hell with it..." I ended up making my thread affinity user-controllable so that I can tell it which processor IDs are REAL cores...

[bob]

Is not so simple:

I explain better, our aim is to set the thread affinity to different physical cores, so I need to know if CPUX is on a different core than CPUY

I see, I thought you only need to detect HT.

Aren't the logical cores interleaved? Like each two logical cores are 1 physical (at least affinity on Windows seems to work this way, also mentioned in one othe links you sent)
This assumption might not hold in the future though...

I have seen the following:

10 physical cores. With HT enabled, you get 20 logical cores, numbered 0-19. Which share a core?

(1) 0 and 1, 2 and 3, etc.

(2) 0 and 10, 1 and 11, etc.

BOTH happen. And of course, then there is IBM with 20 logical cores per physical core.

And once upon a time, when there was a non-power-of-two number of physical cores, all bets were off in both linux and windows.