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Should tests run on a two CPU system?

Is it necessary for QA to run multithreaded programms on systems with
two CPU's and separate Caches or will one Dualcore CPU be enough for
the usual posix thread based Apps?

0
llothar
12/1/2007 1:41:45 AM
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On Nov 30, 7:41 pm, llothar <llot...@web.de> wrote:
> Is it necessary for QA to run multithreaded programms on systems with
> two CPU's and separate Caches or will one Dualcore CPU be enough for
> the usual posix thread based Apps?


The answer to that is specific to the system you're working on.  FWIW,
in the case of x86, a dual core CPU should be enough much of the
time.  All dual core CPUs have at least separate L1 caches for the two
cores.  Where you can get bitten is in cache line thrashing between
sockets, which may be hidden by the relatively fast shared (higher
level) cache on a dual core chip.
0
robertwessel2
12/1/2007 4:57:33 AM
In article 
<514f63dd-c93d-4e8f-9186-be9b43085724@e10g2000prf.googlegroups.com>, 
llothar@web.de (llothar) wrote:

> Is it necessary for QA to run multithreaded programms on systems with
> two CPU's and separate Caches or will one Dualcore CPU be enough for
> the usual posix thread based Apps?

When testing for reliability, rather than performance, we find a few 
problems show up on systems with four cores that don't show up on ones 
with two cores. These are almost certainly in the category of "problems 
that could show up on two cores, and almost never manage to do so, but 
show up on four cores regularly". 

It is extraordinarily hard to be sure that one has got rid of *all* 
intermittent problems in multi-threaded code. 

-- 
John Dallman, jgd@cix.co.uk, HTML mail is treated as probable spam.
0
jgd
12/1/2007 12:43:00 PM
"llothar" <llothar@web.de> wrote in message 
news:514f63dd-c93d-4e8f-9186-be9b43085724@e10g2000prf.googlegroups.com...
> Is it necessary for QA to run multithreaded programms on systems with
> two CPU's and separate Caches or will one Dualcore CPU be enough for
> the usual posix thread based Apps?

Test on as many multi-processor/core systems you can get your hands on. BTW, 
multi-core is analog of SMP on a chip. 

0
Chris
12/3/2007 4:23:46 AM
On Nov 30, 5:41 pm, llothar <llot...@web.de> wrote:

> Is it necessary for QA to run multithreaded programms on systems with
> two CPU's and separate Caches or will one Dualcore CPU be enough for
> the usual posix thread based Apps?

It depends on what QA is trying to do. There are two schools of
thought on this:

1) QA should use hardware as much like what the programs are intended
to run on. This way, realistic performance can be gauged.

2) QA should use hardware on which the software is most likely to
fail, even though realistic performance can't be gauged.

If you follow school of though 1, then yes. If 2, then quad-core would
likely be best. Of course, some bugs pop up best with a single CPU
(especially certain types of livelock where another CPU can come along
and 'save' you).

DS
0
David
12/3/2007 7:47:18 PM
On Dec 4, 2:47 am, David Schwartz <dav...@webmaster.com> wrote:

> If you follow school of though 1, then yes. If 2, then quad-core would
> likely be best. Of course, some bugs pop up best with a single CPU
> (especially certain types of livelock where another CPU can come along
> and 'save' you).

Okay so i will try to get a quadcore as my next system and some of
the
larger SUN Servers with more then 4 cpus. I've seen a E3800 with 10
CPU's
(slow 400Mhz each) for 200 Euro on EBay the last time. Slow but maybe
the ultimate strange system for testing.
0
llothar
12/4/2007 10:38:56 AM
llothar wrote:
> On Dec 4, 2:47 am, David Schwartz <dav...@webmaster.com> wrote:

>> If you follow school of though 1, then yes. If 2, then quad-core would
>> likely be best. Of course, some bugs pop up best with a single CPU
>> (especially certain types of livelock where another CPU can come along
>> and 'save' you).

> Okay so i will try to get a quadcore as my next system and some of
> the
> larger SUN Servers with more then 4 cpus. I've seen a E3800 with 10
> CPU's
> (slow 400Mhz each) for 200 Euro on EBay the last time. Slow but maybe
> the ultimate strange system for testing.

I bet you spend more than 200 Euro on efforts to get extra heat out of
your machine room after you install that bad boy.  :-)

Speaking of ultimate strange systems, I believe you can get the old
MBus-based SPARC systems to run with MBus processor boards of different
speeds.  So go get yourself an old SPARCcenter 2000 with 10 MBus slots
and go to town with possibly 40 Mhz, 45 MHz, 50 MHz, 60 MHz, 75 MHz,
and 85 MHz CPUs, some of which are SuperSPARC-I type and some of which
are SuperSPARC-II, all running together on the same system.  Since the
operating system doesn't (AFAIK) know to prefer faster CPUs, you may
get some charming scheduling effects.  But good luck getting just the
right configuration to get the system to run.  (It's not exactly
supported.)

   - Logan
0
Logan
12/5/2007 3:14:53 AM
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