[ug-bosug] reg: SPARC Processor

[Binu Jose Philip]

On Thu, Aug 6, 2009 at 2:01 PM, gopi krishnan<www.gopi.com at gmail.com> wrote:

>>What is the concept called CMT Microprocessor?

> Am sorry,
> I find it's very difficult to understand. Please give me simple processor
> like 8BIT or 16 BIT or any other basic Processor. Which will help me to
> understand about SPARC. My background have little bit electronics, most of
> algorithms, software engineering, Compiler design, also little bit
> Microprocessor such as 8085, 8086, SICx, 8015?micro controller.

It is not SPARC as such which is different. SPARC or ultraSPARC is like
any other RISC tending to CISC cpu. Constant width instructions with
reordering and a 'comparatively' simple instruction set, a lot of registers
and deep pipelines. The CMT concept is different.

Think of CMT as a very crude Time DIvising multiplexing for instruction
streams from multiple threads. Ordinary CPUs loads instructions from
a single thread at any given time. There is a big delay while data is fetched
from main memory. The CPU waits drumming it's non-existent fingers
wasting all those cycles. Such waits are bad for pipelines further degrading
performance.

A CMT cpu can load instructions and data from multiple threads at the
same time. If it is executing instructions from one thread and there is
a delay in fetching data, the cpu can execute instructions from another
thread. And then if  the second thread waits for memory access, the
CPU switches to the next thread and then to the next one and then back
to the first one. So at any given time a single CPU or core is executing
instructions from 4 threads at the same time.

This works very well if the threads are not CPU bound. ie. if threads
access main memory often. There is ample opportunity for all threads
to run. If any one thread is CPU bound, then that thread keeps running
without giving any of the other threads a chance. CMT is thus very good
for a particular kind of workload.

This explains CMT:
http://developers.sun.com/solaris/articles/chip_multi_thread.html#1

cheers
Binu

> On Wed, Aug 5, 2009 at 3:08 PM, Saurabh Vyas <Saurabh.Vyas at sun.com> wrote:
>>
>> HI Gopi,
>>
>> Please read about CMT (Chip Multi Threading) at
>> http://www.hpcaconf.org/hpca11/papers/23_x_spracklen-chipmultithreading-1.pdf
>>
>> HTH,
>> ~Saurabh
>>
>> gopi krishnan wrote:
>>>
>>> Hi,
>>>
>>> What is the concept called CMT Microprocessor?
>>>
>>> Thanks&Regards,
>>> Gopi&Krishnan S
>>>
>>> On Wed, Aug 5, 2009 at 2:27 PM, Tirthankar <no-reply at opensolaris.org
>>> <mailto:no-reply at opensolaris.org>> wrote:
>>>
>>> ? ?Check out http://www.opensparc.net/
>>> ? ?You will get all information on SPARC processors.
>>>
>>>
>>> ? ?Thanks,
>>> ? ?Tirthankar
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