Re:[OT] deluge of overrated posts
by
Anonymous Coward
·
· Score: 4
[OT] deluge of overrated posts (Score:5, Interesting)
the irony is thick.
Mosix is definitely cool...
by
Anonymous Coward
·
· Score: 4
I'm in an academic department that does a veritable sh*tload of computations, and we've been using it
for nearly a year to load-balance a bunch of P2-350s. It's great, makes those machines feel "loved", and keeps people's research on progress.
It's great when you can break up your problem/program into a bunch of smaller ones.
But it's not perfect, and as with all clustering solutions, doesn't do the hard work (algorithm parallelizing) by itself.
However, it is going to form the backbone of our dept system, replacing a pair of big-iron Sun servers...
It should be noted that Linux takes longer to switch tasks on the PIII if it was compiled to support SSE2 instructions. Five dollars says that FreeBSD doesn't support them. Perhaps those benchmarks would have showed different results if the kernel had been built without SSE2 support?
[OT] deluge of overrated posts
by
AiX2
·
· Score: 4
The past month on Slashdot, a disportionate number of posts have been marked +5 Interesting. In the past, +5 Interesting has been reserved for especially well written and clued in posts. Slashdot needs to change either the number of people receiving moderation points or increase the maximum a post can be rated to 10. If this were to take effect, I could simply read the 5-6 best written or insightful comments instead of the posts people feel they have to waste their mod points on.
So far MOSIX was developed 7 times, for different versions of UNIX and architectures. It has been used as a production system for many years. The first PC version was developed for BSD/OS. The latest version is for Linux on X86/Pentium/AMD platforms.
Yes, they did start out basing their system on proprietary kernels, then they moved to BSD, then to Linux. The current work is not about the basic idea anymore, moving processes around somehow, but about things like distributed virtual memory, distributed file systems, and migration strategies.
This isn't "playing catch-up", it is cutting edge research by the people who did the original work moving to the BSD and Linux platforms because they are more widely available, are better supported, are easier to license and share, and have more software available for them.
Re:Finally, something resembling clustering for Li
by
glenmark
·
· Score: 4
My comments were not rooted in ignorance, but rather an intimate familiarity with the technology developed by the DIGITAL engineers who INVENTED clustering, back in the days before the term was diluted by use in situations that have no relationship to the original application of the term.
Veritas Cluster Server is actually a clustering technology (only marginally, since, like Microsoft clustering, it employs a shared-nothing model). I have no problem with the application of the term here.
Arrowpoint? No. Load balancing is useful in a cluster (and even more useful when applied to all networking protocols, not just HTTP), but load balancing alone does not a cluster make.
Mosix (homogeneous process environment) is borderline. It just needs the addition of a few key technologies to qualify. (DLM, device sharing)
Beowulf (distributed parallel computing environment), while an interesting and useful technology, has nothing whatsoever to do with clustering! The term is misused here, and that is what annoys me. If you were to classify Beowulf as a clustering technology, you would also have to call every computer participating in SETI@home a single cluster, which it clearly is not...
And no, that list is far from complete. No mention of HP's clustering technology, Compaq's OpenVMS Clusters, True64 Unix TruClusters, or Tandem NonStop Fault-Tolerant clusters, or Microsoft Clustering (although, again, that is a VERY weak form of clustering, and lacking in several respects).
Essentially, this is an arguement over semantics, over the definition of the term "cluster". I merely oppose dilution of the meaning by applying it to lesser technologies which have no relationship with the original meaning of the term.
-- *** Quantum Mechanics: The Dreams of Which Stuff is Made ***
A quick primer on types of paralell systems.
by
landley
·
· Score: 5
There are traditionally three different types of paralell processing systems: SMP, NUMA, and networked clusters like Beowulf. In reality, these form a continuous range, with SMP at one end, Beowulf at the other, and NUMA in the middle.
SMP is Symmetrical Multi-Processing, or one computer with multiple processors just like multiple hard drives, multiple serial ports, or multiple banks of RAM. In an SMP setup, each processor has equal access to the other system resources, and although they may need locking to avoid stomping on each other's activities, it's no more expensive for processor #2 to access a certain resource (such as an area of main memory) than it is for processor #5 to do so. Thus there's no real reason to shuffle processes around to be "closer" to some other resource.
The other end of the spectrum is message passing networked clustering, like beowulf, where isolated systems (each with its associated set of resources) accept complete tasklets, work on them more or less alone, and output the results. Accessing resources from the rest of the cluster is very expensive, and you try not to do it more than absolutely necessary (once per transaction). A message comes in with all the info a node needs to do its work, and the node sends a message back out with the result and to announce it's ready for the next mouthful.
NUMA is in between, and it stands for Non-Uniform Memory Architecture. You have a bunch of similar processors, like in SMP, but some resources are "close" to each processor and some are far away.
Remember, clusters own resources outright, this is my node's memory. On SMP all processors access a pool of shared resources (like main memory) at the same speed (hence symmetrically). On NUMA, processor #53 -CAN- access memory over by processor #1736, but it'll take much longer than if it accesses memory near itself. It'll block, it'll have wait states. (Just like accessing a page swapped to the hard drive vs accessing one in memory.)
The thing is, as systems on either end become more complex they move towards NUMA. Think mondo SMP systems with dozens of processors, each of which has megabytes of L1 cache. You want to keep stuff "in cache" rather than accessing main memory, and sometimes you wan't to access something that's currently in some other processor's cache. Cache line pollution and such. That's a NUMA type of problem.
From the other end, once you start connecting beowulf clusters together with really high speed interconnects (like gigbit ethernet or myrinet, and often speed here is more a question of latency than bandwidth,) and start teaching them how to pretend to be one big shared memory image by page faulting through the network, you're approcaching NUMA from the other end. Stuff's in my machine's memory locally right now, and swapping it in from some other guy's memory (and swapping out some of my stuff to make room for it) is something I only want to do when absolutely necessary, because it slows me down.
MOSIX is taking beowulf clusters in the direction of NUMA. This is a good thing, it makes them more flexible and capable, but it opens up a whole can of worms to optimize it properly. (Not a new can of course, the kernel hackers are already dealing with a rather significant portion of NUMA's issues just trying to get 32 processor alphas to work smoothly.) If the interconnects between clusters were perfect, we could just treat it as one big SMP machine. Then again if our hard drives were as fast as our ram we wouldn't try so hard to minimize swapping, would we?
You could still just treat MOSIX as SMP instead of NUMA if you don't want to optimize your performance. And for many things that's a fine solution, just distributing it cross the cluster gives you all the performance you need, and adding nodes is more cost effective than rewriting your app for greater speed in the new environment.
But performance hits of thrashing all your pages through the network can be just as bad as thrashing them in and out of the swap partition. And performance is the only reason we're using clusters in the first place, isn't it?
And NUMA optimization just makes maintaining locality of reference, streamlined locking, and minimizing contention for commonly accessed resources even MORE important. It's the same kind of thing you'd do on a normal SMP machine anyway, it just has more of an impact, because there's more inefficiency to optimize away.
Slashdot Mirror
the irony is thick.
I'm in an academic department that does a veritable sh*tload of computations, and we've been using it for nearly a year to load-balance a bunch of P2-350s. It's great, makes those machines feel "loved", and keeps people's research on progress. It's great when you can break up your problem/program into a bunch of smaller ones. But it's not perfect, and as with all clustering solutions, doesn't do the hard work (algorithm parallelizing) by itself. However, it is going to form the backbone of our dept system, replacing a pair of big-iron Sun servers...
It should be noted that Linux takes longer to switch tasks on the PIII if it was compiled to support SSE2 instructions. Five dollars says that FreeBSD doesn't support them. Perhaps those benchmarks would have showed different results if the kernel had been built without SSE2 support?
- 05 -03-007-20-NW-KN
http://linuxtoday.com/news_story.php3?ltsn=2001
The past month on Slashdot, a disportionate number of posts have been marked +5 Interesting. In the past, +5 Interesting has been reserved for especially well written and clued in posts. Slashdot needs to change either the number of people receiving moderation points or increase the maximum a post can be rated to 10. If this were to take effect, I could simply read the 5-6 best written or insightful comments instead of the posts people feel they have to waste their mod points on.
(just my drunken rambling)
--Ryan
Yes, they did start out basing their system on proprietary kernels, then they moved to BSD, then to Linux. The current work is not about the basic idea anymore, moving processes around somehow, but about things like distributed virtual memory, distributed file systems, and migration strategies.
This isn't "playing catch-up", it is cutting edge research by the people who did the original work moving to the BSD and Linux platforms because they are more widely available, are better supported, are easier to license and share, and have more software available for them.
My comments were not rooted in ignorance, but rather an intimate familiarity with the technology developed by the DIGITAL engineers who INVENTED clustering, back in the days before the term was diluted by use in situations that have no relationship to the original application of the term.
And no, that list is far from complete. No mention of HP's clustering technology, Compaq's OpenVMS Clusters, True64 Unix TruClusters, or Tandem NonStop Fault-Tolerant clusters, or Microsoft Clustering (although, again, that is a VERY weak form of clustering, and lacking in several respects).
Essentially, this is an arguement over semantics, over the definition of the term "cluster". I merely oppose dilution of the meaning by applying it to lesser technologies which have no relationship with the original meaning of the term.
*** Quantum Mechanics: The Dreams of Which Stuff is Made ***
SMP is Symmetrical Multi-Processing, or one computer with multiple processors just like multiple hard drives, multiple serial ports, or multiple banks of RAM. In an SMP setup, each processor has equal access to the other system resources, and although they may need locking to avoid stomping on each other's activities, it's no more expensive for processor #2 to access a certain resource (such as an area of main memory) than it is for processor #5 to do so. Thus there's no real reason to shuffle processes around to be "closer" to some other resource.
The other end of the spectrum is message passing networked clustering, like beowulf, where isolated systems (each with its associated set of resources) accept complete tasklets, work on them more or less alone, and output the results. Accessing resources from the rest of the cluster is very expensive, and you try not to do it more than absolutely necessary (once per transaction). A message comes in with all the info a node needs to do its work, and the node sends a message back out with the result and to announce it's ready for the next mouthful.
NUMA is in between, and it stands for Non-Uniform Memory Architecture. You have a bunch of similar processors, like in SMP, but some resources are "close" to each processor and some are far away.
Remember, clusters own resources outright, this is my node's memory. On SMP all processors access a pool of shared resources (like main memory) at the same speed (hence symmetrically). On NUMA, processor #53 -CAN- access memory over by processor #1736, but it'll take much longer than if it accesses memory near itself. It'll block, it'll have wait states. (Just like accessing a page swapped to the hard drive vs accessing one in memory.)
The thing is, as systems on either end become more complex they move towards NUMA. Think mondo SMP systems with dozens of processors, each of which has megabytes of L1 cache. You want to keep stuff "in cache" rather than accessing main memory, and sometimes you wan't to access something that's currently in some other processor's cache. Cache line pollution and such. That's a NUMA type of problem.
From the other end, once you start connecting beowulf clusters together with really high speed interconnects (like gigbit ethernet or myrinet, and often speed here is more a question of latency than bandwidth,) and start teaching them how to pretend to be one big shared memory image by page faulting through the network, you're approcaching NUMA from the other end. Stuff's in my machine's memory locally right now, and swapping it in from some other guy's memory (and swapping out some of my stuff to make room for it) is something I only want to do when absolutely necessary, because it slows me down.
MOSIX is taking beowulf clusters in the direction of NUMA. This is a good thing, it makes them more flexible and capable, but it opens up a whole can of worms to optimize it properly. (Not a new can of course, the kernel hackers are already dealing with a rather significant portion of NUMA's issues just trying to get 32 processor alphas to work smoothly.) If the interconnects between clusters were perfect, we could just treat it as one big SMP machine. Then again if our hard drives were as fast as our ram we wouldn't try so hard to minimize swapping, would we? You could still just treat MOSIX as SMP instead of NUMA if you don't want to optimize your performance. And for many things that's a fine solution, just distributing it cross the cluster gives you all the performance you need, and adding nodes is more cost effective than rewriting your app for greater speed in the new environment.
But performance hits of thrashing all your pages through the network can be just as bad as thrashing them in and out of the swap partition. And performance is the only reason we're using clusters in the first place, isn't it?
And NUMA optimization just makes maintaining locality of reference, streamlined locking, and minimizing contention for commonly accessed resources even MORE important. It's the same kind of thing you'd do on a normal SMP machine anyway, it just has more of an impact, because there's more inefficiency to optimize away.
Rob