[Beowulf] Xgrid and Mosix (fwd from john@rudd.cc)

Douglas Eadline, Cluster World Magazine deadline at clusterworld.com
Sat Jan 1 07:40:44 PST 2005


These two pages are useful when considering Mosix

What does not migrate:
http://howto.x-tend.be/openMosixWiki/index.php/don't

what does migrate:
http://howto.x-tend.be/openMosixWiki/index.php/work%20smoothly


ClusterWorld just ran a feature on OpenMosix

http://www.clusterworld.com/issues/dec-04-preview.shtml


Doug

On Thu, 30 Dec 2004, Eugen Leitl wrote:

> ----- Forwarded message from John Rudd <john at rudd.cc> -----
> 
> From: John Rudd <john at rudd.cc>
> Date: Wed, 29 Dec 2004 19:37:02 -0800
> To: xgrid-users at lists.apple.com
> Subject: Xgrid and Mosix
> X-Mailer: Apple Mail (2.619)
> 
> 
> I see in the archives that someone asked about OpenMosix back in 
> September ( 
> http://lists.apple.com/archives/xgrid-users/2004/Sep/msg00023.html ), 
> but I didn't see any responses.  So I thought I'd ask too, but with a 
> little more detail.
> 
> The thing that I find interesting about the Mosix style distributed 
> computing environment is that applications do NOT need to be re-written 
> around them.  Mosix abstracts the distributed computing cluster away 
> from the program and developer in the same way that threads abstract 
> multi-processing away from the program and developer.  Under Mosix, any 
> program, without having to be written around any special library, 
> without having to be relinked or recompiled, can be moved off to 
> another processing node if there are nodes that are significantly less 
> busy than yours.  And, AFAIK, any multi-threaded application can make 
> use of multiple nodes (with threads being spawned on any host that is 
> less loaded than the current node).  Imagine taking a completely 
> mundane but multi-threaded application (I'll assume Photoshop is 
> multi-threaded and use that as an example).  Suddenly, without having 
> to get Adobe to support Xgrid, you can use Xgrid to speed up your 
> Photoshop rendering.
> 
> It seems to me that a similar set of features could be added to Xgrid.  
> The threading and processing spawning code within the kernel could be 
> extended by Xgrid to check for lightly loaded Agents, and move the new 
> process or thread to that Agent.  Only the IO routines would need to 
> exist on the Client (and even then, maybe not: if every node has 
> similar filesystem image, then only the UI (for user bound 
> applications) or primary network interface code (for network 
> daemons/servers) needs to run on the original Client system).  From 
> what I recall, the mach microkernel already makes some infrastructure 
> for this type of thing available, it just needs to be utilized, and 
> done deep enough in the kernel that an application doesn't need to know 
> about it.
> 
> 
> Though, that does bring up one consideration: I have a friend who did a 
> lot of distributed computing work when he was working for Flying 
> Crocodile (a web hosting company that specialized in porn sites, where 
> his distributed computing code had to support multiple-millions of hits 
> per second).  His experience there gave him a concern about Mosix style 
> distributed computing.  One of the advantages of something like Beowulf 
> is that the coder often needs to control what things need to be kept 
> low latency (must use threads for SMP on the local processor) and what 
> things can have high latency (can use parallel code on the network), 
> and the programming interface type of distributed computing gives them 
> that flexibility.
> 
> The idea that I suggested was something like nice/renice in unix, where 
> you could specify certain parallelism parameters to a process before 
> you run it, or after it is already running.  For example, instead of 
> "process priority", you might specify a sort of "process affinity" or 
> "thread affinity".  For process affinity, a low number (which means 
> high affinity, just like priority and nice numbers) means "when this 
> process creates a child, it must be kept close to the same CPU as the 
> one that spawned it".  Thread affinity would be the same, but for 
> threads.  A default of zero means "everything must run locally".  A 
> high number means "I can tolerate more latency" (so, "latency 
> tolerance" would be the opposite of "affinity").  (it occurs to me 
> after I wrote all of this that it might be easier for the end user to 
> think in terms of "latency tolerance" instead of "process affinity", 
> high latency = high number, instead of the opportunity for confusion 
> that affinity has since the numbers go in the opposite direction ... I 
> hope all of that made sense)
> 
> A process with a low process affinity (high number) and a high thread 
> affinity (low number) means that it can spawn new 
> tasks/processes/applications anywhere in the network, but any threads 
> for it (or its sub-processes) must exist on the same node as its main 
> thread.  Or, if you want all of the applications to be running on your 
> workstation/Client, but run their threads all over the network, then 
> you set a high process affinity (low number), and a low thread affinity 
> (high number).
> 
> I would have the xgrid command line tool have such a facility (I don't 
> know if it does already or not, I haven't really done much with xgrid) 
> similar to both the "nice" and "renice" commands.  I would also add a 
> preference pane that allows the user to set a default process affinity, 
> a default thread affinity, and a list of applications and default 
> affinities for each of those applications (so that they can be 
> exceptions to the default, without the user having to set it via 
> command line every time).  Last, I would add a tool, possibly attached 
> to the Xgrid tachometer, which would allow me to adjust an affinity 
> after a program was running.
> 
> The only thing up in the air is the ability to move a running thread 
> from one node to another while it's running (well, during a context 
> switch, really).  I know a friend of mine at Ga Tech was doing PhD 
> research on that (portable threads) 10ish years ago, but I don't know 
> if it got anywhere.  But, that would allow someone to lower the number 
> of an application's affinity while it's running, thus recalling the 
> threads or processes from a remote Agent to the local Client (the 
> scenario being I have a laptop that is an Xgrid Client, and I start 
> running applications that spread out across the network ... then I get 
> up to leave, so I lower the affinity numbers of everything so that the 
> tasks and threads come back to my laptop, running slower now that they 
> have fewer nodes to run upon, but still running (or sleeping, as the 
> case might be)).
> 
> 
> So ... all of that leads up to: does anyone know if Xgrid is working on 
> this type of Application-Transparent Distributed Computing that Mosix, 
> OpenMosix, and I think OpenSSI have?  I think it would be a natural 
> extension to Xgrid: Apple is trying to make this as "it just works" as 
> possible, so it seems that it should not only be easy for the sysadmin 
> to set up the distributed computing cluster, but easy/transparent for 
> the developer, too (in the same way that threads made Multi-Processing 
> easier and more abstract for the developer, this type of distributed 
> computing makes threads not just a multi-processing model, but a 
> distributed computing model).  Ultimately, it even makes distributed 
> computing easy for the user: they don't need to learn how to re-code a 
> program (or coerce a vendor into making a distributed version of their 
> application), any multi-threaded application will use multiple nodes, 
> and even single-threaded non-distributed applications can be run on 
> remote nodes.  That seems like a powerful "it just works" capability to 
> me.
> 
> (the main drawback of Mosix, OpenMosix, and OpenSSI from my perspective 
> is that they're Linux only, specifically developed for the Linux kernel 
> ... but I'd really love to see something like them available for Mac OS 
> X)
> 
> Thoughts?
> 
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