[Beowulf] multi-threading vs. MPI

Chris Samuel csamuel at vpac.org
Wed Dec 12 20:50:41 PST 2007


On Mon, 10 Dec 2007, Mark Hahn wrote:

> threads, of course, are antithetical to security, since the whole
> point is freedom to read/write anything.

This is one of the reasons that Tridge (of Samba fame) rants against 
the use threads by people thinking that they'll be faster than 
independent processes.. :-)

Viz:

http://lists.samba.org/archive/samba-technical/2004-December/038301.html

> no, you're still clinging to the notion that threads are somehow
> inherently faster than processes. They aren't. They are inherently 
> slower, no matter what OS you are talking about. 
>
> Some OSes might implement processes so badly that threads come out 
> ahead. It is fundamental computer science that doing operations in a 
> threaded environment will be slower than doing operations in an
> equivalent process based environment, because they have to do more
> work. 
> 
> Using processes allows you to take advantage of a hardware memory
> protection system. Using threads doesn't. 

and:

http://lists.samba.org/archive/samba-technical/2004-December/038298.html

> What is it about the word "thread" that people find so damn sexy?
>
> Maybe it needs a name change 
> "slow-as-hell-no-memory-protection-locks-dont-work" API might be
> suitable, but I suspect the standards committees wouldn't like that 
> one. 
> 
> The MMU was added to CPUs for a very good reason. Why is it so hard
> to understand that trying to avoid it is a bad idea? 

cheers,
Chris
-- 
Christopher Samuel - (03) 9925 4751 - Systems Manager
 The Victorian Partnership for Advanced Computing
 P.O. Box 201, Carlton South, VIC 3053, Australia
VPAC is a not-for-profit Registered Research Agency
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