🚀 go-pugleaf

>>>>> "warr" == warr  <warren22432@yahoo.com> writes:

    warr> if a program is written for single CPU only, even though
    warr> your OS is coordinating the 2 cpus and this program may be
    warr> running on 2 cpus, but they are not running
    warr> concurrently. they are still sequential processing.

Right.

    warr> and the kernel has to switch between the 2 CPUs for 1 single
    warr> process.

Why?  A smart  OS (e.g. Linux) will schedule the  CPUs wisely, so that
one single CPU serves that  single-thread process, and it does this by
running itself  on the second  CPU.  IOW, if  you have only  1 process
running, that process  will occupy 1 CPU, and the OS  makes use of the
other  for its own  tasks: job  scheduling, disk  scheduling, handling
user inputs (interrupts), etc.


    warr> it is definitely slower than the single cpu
................^^^^^^^^^^
    warr> without interprocessor communication.

"definite" is the most wrong word here.

Interprocess communication?  When  2 completely separate processes are
running on  the 2 CPUs, why is  there a need to  do any interprocessor
communication?   This  interprocessor  communication  may be  big  for
multi-threaded processes,  as they share  memory space, and  hence may
trigger cache-coherence, which incurrs  overhead.  However, when the 2
CPUs are  concentrating on separate physical addresses,  how come they
need to inter-communication?



    warr> I didn't see any benchmarks on Linux.

But  user  experience is  very  consistent:  the  system appears  more
responsive.  This is no unreasonable.  Even when running just a single
CPU-intensive process, there  is still the other CPU  ready to respond
to mouse clicks, keypresses, etc.



    warr> but in windows, there are lots of benchmarks that shows
    warr> faster execution on a single CPU than a dual cpu if you use
    warr> a program that isn't multi threaded.

That only  shows that Windows  suck.  Hardly are these  benchmarks any
proof that dual systems  cannot work efficiently under Linux.  Windows
is very  insecure, too.  Would you  then generalize this  and say that
all computer systems (not just PCs) are insecure?



    warr> OS is Dual CPU complient doesn't optimize your single
    warr> threaded process.

It depends  on how  that OS is  implemented.  A  stupid implementation
won't help, of course!  A smart one does.  That's the same as computer
programs.  Stupid people would use  O(2^n) algorithms for a task where
every smart people would implement O(n) algorithms.  That doesn't mean
the task is difficult, just the programmer is stupid.


-- 
Lee Sau Dan                     ���u��(Big5)                    ~{@nJX6X~}(HZ) 

E-mail: danlee@informatik.uni-freiburg.de
Home page: http://www.informatik.uni-freiburg.de/~danlee