On 08/19/2011 02:15 PM, David W Noon wrote:
Threads are not tied to processors.
I do know that in Linux the scheduler tries to keep a thread in a core
if possible (even after re-scheduling the thread after preemption). This
greatly increases cache performance.
This is especially true in
"managed" languages, where threads usually have process scope and
consequently all run on the same CPU. [I.e. a thread with process scope
cannot have CPU affinity distinct from that of the main thread in the
process, whereas a thread with system scope can run wherever the
operating system's CPU dispatcher sends it, possibly constrained by
that thread's own CPU affinity mask.]
While I do understand what you mean, I never heard that defining CPU
affinity in a way that a process only is allowed to use one core for all
it's threads. If this is set, of course parallel tasks don't make any
sense at all. I suppose that this can be set for special purposes, but I
don't thinks that it's a standard setting (e.g. in Linux).
As a growing "class" of programs are defined to take advantage from a
multi-core System - and I suppose most do this by distributing
cycle-hungry tasks towards multiple threads - I understand that the
normal way of the OS is to allow for multiple CPUs for a single
application.
-Michael
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