Re: About Parallelism

Iwo Mergler <Iwo.Mergler@xxxxxxxxxxxxxxxxxxxx> wrote:


Thank you, Iwo. You are quite correct: the objdump's did not reveal any
direct parallelism, though I can't speak for the syscalls.
I was well aware of watching execution profiles, so perhaps I should
have asked: how to ensure that mmulti-threading will assign multiple
CPU's to my threads? But you have now answered that question as well.

Thanks again,
Scott
=============

: Scott J. McCaughrin wrote:

: > I have a multi-CPU machine, but I suspect my compilers may not be
: > taking advantage of parallelism. Yes, I am doing penty of multi-
: > threading, but how can I make sure that the implementation is
: > actually making use of the multiple CPU's (Xeons)?
: > As a brute-force approach, I could 'objdump' my pthreads library
: > and study its gas code to see what happens. Is there a less tedious
: > alternative?
: >
: > Thanks, Scott

: Hi Scott,

: you will not find any parallel magic in the objdump output.

: Modern PC processor cores depend on deep pipelines and caches
: for their performance. This makes it very expensive to split
: a program across multiple cores in the way you seem to expect.

: Thus, compilers for PCs compile programs for a single core.

: The parallelism is implemented by the OS at thread/task level.
: If you have a multi-threaded program, the OS will distribute
: the active threads over different cores.

: Please note the keyword here is 'active'. Most programs have
: rarely more than two active threads at any time.

: As Josef said, if your aim is to load all your CPUs to 100%,
: write a bunch of computing threads, each operating on their
: own variables and without I/O. The OS will distribute them
: among the cores.

: The world you described, where the compiler extracts intrinsic
: parallelism from a program and distributes it across cores,
: does indeed exist. These methods are used heavily with vector
: processors, signal processors, media processors, GPUs, etc.

: These architectures are specifically designed for fine-grained
: parallelism. PCs are not.

: Kind regards,

: Iwo


--
Scott McCaughrin

.

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