std.parallelism: Request for Review

[Russel Winder]

On Mon, 2011-02-28 at 10:41 +0100, Don wrote:
[ . . . ]
> As the name says, it is * cores per CPU *. That is _not_ the same as the 
> total number of cores in the machine.

I guess then the missing extension is to have a function that returns an
array opf processor references so that the core count can be measured?

> The documentation probably doesn't state that strongly enough, but 
> currently there is no known bug in the implementation of 
> core.cpuid.coresPerCPU.

OK so my complaints were somewhat misdirected, apologies.

The fact remains though that it seems there is no way in D or Phobos to
pick up the number of "processors" available to a Linux or Mac OS X
machine -- I guess the same applies to Windows but I personally don't
use that OS so don't really care about that one ;-)

> It's an OS issue, anyway: just because a machine has 64 cores, is no 
> guarantee that it will give you access to all of them. std.parallelism 
> shouldn't be using core.cpuid for that purpose.

I had thought you were arguing that D/Phobos couldn't rely on waiting
for OS functionality, that it had to use direct access to the processor
techniques.  Maybe I misunderstood what you were saying.  If so, my
apologies.

Linux claims to have 8 processors on my twin-Xeon box.  std.parallelism
therefore needs some form of support from D and/or Phobos to say "how
many parallel threads can this platform sustain".  All other parallelism
frameworks I use handle this no problem.

I accept your argument about core.cpuid and so will not investigate it
further, other than to say it needs to work on 64-bit processors as well
as 32-bit ones.  The campaign now must be to have an OS query capability
to find the number of processors.

Thanks.

-- 
Russel.
=============================================================================
Dr Russel Winder      t: +44 20 7585 2200   voip: sip:russel.winder at ekiga.net
41 Buckmaster Road    m: +44 7770 465 077   xmpp: russel at russel.org.uk
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