[mpich-discuss] Why is my quad core slower than cluster

[Elvedin Trnjanin]

http://softwarecommunity.intel.com/Wiki/Linux/719.htm

Is that the issue?

"background

linux gcc carries on the Unix tradition from the early days of C, when 
the run-time libraries weren't considered as part of the compiler.  
Thus, there is little coordination between compiler and library 
versions.  A normal compiler update will not update library functions 
such as memcpy().

New compiler installations, for example those from Intel, inherit most 
of the run-time support from what is provided (at least optional) in the 
linux installation.  This contrasts with the situation on Windows, where 
Intel compilers require a Microsoft compiler installation to provide the 
libraries, while gcc requires a companion run-time support such as 
cygwin or mingw.

Much of the OS support as well as C run-time support on linux is 
incorporated in the glibc library.  Although this is a Free Software 
Foundation project, and the bug report data base 'glibc bugzilla' is 
open to public inspection, the developer communications don't appear on 
a public list.  There is no visible public help forum or mail list.  It 
is not generally feasible to update glibc except as supported by the 
linux distribution.

Intel compilers modify the situation; for example, they pre-empt a few 
of the standard C functions, including memcpy().  As combined gcc/icc 
usage is supported, this leads to confusion about which run-time version 
is in effect."

Darius Buntinas wrote:
>
> But the kernel is not doing the memcpy.  The memcpy used in mpich2 for 
> intel x64_64 is from libc.  Scott, do you know if there is a problem 
> with libc memcpy also?
>
> -d
>
> On 07/10/2008 09:00 AM, Scott Atchley wrote:
>> On Jul 8, 2008, at 12:35 PM, zach wrote:
>>
>>> I am using a cluster.
>>> Each pc has two cpus and they are Xeon. Each cpu has 4GB, i think red
>>> hat is running.
>>>
>>> I also use a pc at home- quad core intel chip, 8gb ram, ubuntu.
>>>
>>> Both are using mpich.
>>>
>>> I have found that my home pc is only running about 1/3 the speed of
>>> the cluster, and the number of processes (4) and code is the same.
>>>
>>> Can anyone tell me if this is typical, and why, or am I not optimizing
>>> something properly?
>>>
>>> Thanks
>>> Zach
>>
>> Which processor (Harpertown?). Which kernel?
>>
>> Kernels <= 2.6.20 use the wrong memory copy routine for Intel Core2 
>> cpus. Since all of your communication will use memory copy, it will 
>> make a difference.
>>
>> Scott
>>
>