How to find the number of CPUs?

[Tord Romstad]

Hi all,

Is there any simple way for a C/C++ program to find the number of CPUs on the computer it is running? If possible, I would prefer a cross-platform solution, but if the code is not too messy I would also be happy with separate solutions for Unix and Windows.

Tord

[Sven Schüle]

Hi Tord,

I'm afraid there is no cross-platform solution. AFAIK even on different UNIX systems you may need different code (no POSIX standard yet?), although for both Linux and Solaris (o.k., the latter is not a chess platform) probably the same code should work (I did not try):

Code: Select all

#include <unistd.h>
int ncpus = sysconf(_SC_NPROCESSORS_ONLN);

retrieves the number of active ("online") CPUs; this should be less than or equal to the number of CPUs present on the motherboard, which in turn could be retrieved by 'sysconf(_SC_NPROCESSORS_CONF)'.

For Windows, I simply don't know.

Sven

[Alessandro Scotti]

Hi Tord,
there is no simple solution that I know. Although you can find the proper API call for each system, I think the real problem is understanding what information it is actually reporting.
For example if you run Windows, Linux or Solaris on a Intel single-core processor with hyperthreading, you will find the operating system reports 2 processors, which is not what you want in a chess engine.
Likewise, Solaris on the new 8-core Ultra SPARC T1 is reporting 32 processors (each core has 4-way SMT) but I'm not sure it's a good idea to use each of them for searching.
BTW you can use GetSystemInfo() on Windows, and take a look at /proc/cpuinfo on Linux/x86 (which is less clean than sysconf but has more info e.g. about hyperthreading).
Also, a while ago I recompiled and tested Glaurung for Solaris/SPARC and it worked fine IIRC.

P.S. This is going to be off-topic but... got the new Mac, got Quartz Composer, got hooked... Hamsters' in danger!!!

[Dann Corbit]

http://msdn.microsoft.com/library/defau ... fo_str.asp

[Tord Romstad]

Hi all,

Thanks for the replies!

Hi Tord,
there is no simple solution that I know. Although you can find the proper API call for each system, I think the real problem is understanding what information it is actually reporting.
For example if you run Windows, Linux or Solaris on a Intel single-core processor with hyperthreading, you will find the operating system reports 2 processors, which is not what you want in a chess engine.

That's a pity. I suppose I will just have to trust that the users will be smart enough to figure out how many threads they should use, then.

P.S. This is going to be off-topic but... got the new Mac, got Quartz Composer, got hooked... Hamsters' in danger!!!

I don't even know what Quartz Composer is, although I have noticed that there is a program with such a name. Thanks for the warning - I'll try to resist the temptation to have a look at it.

Tord