4 ms·

Sounds good. I have an issue with the "45GHz" claim though - it's kind of like saying your collection of cars can go 2000 mph - you're not actually getting anyw

by ukoki 14y ago

Sounds good. I have an issue with the "45GHz" claim though - it's kind of like saying your collection of cars can go 2000 mph - you're not actually getting anywhere faster.

abcd_f 14y ago
Car analogy is off. Going from A to B is exactly an example of a task that can't be solved in parallel fashion. On the other hand, if you needed to merely cover N miles, then a pool of cars would work just fine.
- josephlord 14y ago
  Many computing problems can't be parallelised and in almost all there are dependencies and synchronisation issues that mean a single double speed CPU is almost always better than two normal ones. Exception might be that when a buggy programme gets locked in a tight loop it will only be able to take half the resources. To use another car analogy. Counting clock speed is like counting the cars max RPM instead of actually measuring the performance. And then they have totalled the max RPM figures as if they have have 90,000RPM engine.
  - alexchamberlain 14y ago
    Conversely, there are many problems, most notably in the low-level mathematics, which can be parallelised. Matrix multiplication for example...
    - josephlord 14y ago
      Yes there are infinitely* many problems that can be parallelised but even in the best case they will only equal the single processor at double the speed. http://home.wlu.edu/~whaleyt/classes/parallel/topics/amdahl.html http://home.wlu.edu/~whaleyt/classes/parallel/topics/amdahl.... I should have referenced Amdahl's law in the previous post but didn't want to misspell it and bother to look it up. *Infinite numbers exist of both parallel and serial computing requirements. Practically there will almost always be additional cost in parallel implementation even if the extra is insignificant such as higher start up cost and coordination for shutdown.
      - mclarkk 14y ago
        Amdahl's Law did throw a damp cloth over the fire of enthusiasm about parallel computing...for a while. But then we got Gustafson's Law: http://en.wikipedia.org/wiki/Gustafson%27s_Law http://en.wikipedia.org/wiki/Gustafson%27s_Law Gustafson and Barsis pointed out that Amdahl assumed a fixed input size. If instead you grow the problem size along with the number of processors, the speedup from parallelism grows indefinitely. Of course, like Amdahl, they assume perfect load balancing and don't factor in communication overhead. But parallel still beats the pants off of serial if we want to keep solving larger and larger problems.
- danbee 14y ago
  Actually it can. If you have 16 people to move and 1 car that seats 4 it will take 4 round trips. 4 cars will do it in 1 one way trip. People = threads and cars = cores.
- laumars 14y ago
  You missed his point. Clock frequencies cannot be combined as it's a measure of the frequency a single core operates at - not how many operations per second can be processed. This is why multi-core CPUs don't say 8GHz even though they have 4x 2GHz cores.
  - abcd_f 14y ago
    Of course I haven't missed the point. You did :) You can nitpick as much as you want, but for a lot of applications it's perfectly OK to sum up the frequencies. A job that can be spread over 8 cores will be executed at about the same time as it would execute on a single core at 8x the frequency
    - laumars 14y ago
      No it wouldn't. You have overhead generated by running threads concurrently (eg thread management, communication between nodes, etc). You have issues where not all threads are going to have the exact same complexity (eg some might consist of more floating point calculations than others), this could even result in threads sitting idle while they wait for another thread on a different core to finish. Plus there's absolutely no precedence for using clock frequencies cumulatively like this anyway (which I've already demonstrated with my multi-core CPU example), thus the figures Adapteva are touting are not only scientifically and mathematically inaccurate, but also breaking established advertising convention too. Thus their figures are incorrect - period. So accusing us of nitpicking incorrect figures is just plain dumb when there's absolutely no merit to the 13GHz figure what-so-ever. [edit] And it's a sad day for geeks worldwide if discussing the correct usage for scientific measurements is considered nitpicking. Had this been Fox News or the Daily Mail, then your view point could be forgiven. But this is a hacker forum, so I'd expect a higher level of technicality rather than simply ignoring counterarguments in such a dismissive manner. :(
      - abcd_f 14y ago
        Describing a gadget in terms of cumulative frequency of its cores is an A-Ok method of giving approximate performance, especially when it's obvious that it's a sum of cores. You and I and anyone moderately interested by this project know exactly what this number means. It is also pretty clear that they haven't meant to mislead or trick someone into thinking that they are building a 1THz computer for $99. So, yeah, it's nitpicking. A better angle would be - given the project and its goals, do you really think it's worth putting them down for something as trivial (and technically correct) as this - Once completed, the Parallella computer should deliver up to 45 GHz of equivalent CPU performance That, as they say on TechCrunch, is a dick move. If anything, they deserve a pat on a back and a donation.

by ukoki 14y ago

Sounds good. I have an issue with the "45GHz" claim though - it's kind of like saying your collection of cars can go 2000 mph - you're not actually getting anywhere faster.

abcd_f 14y ago

Car analogy is off. Going from A to B is exactly an example of a task that can't be solved in parallel fashion. On the other hand, if you needed to merely cover N miles, then a pool of cars would work just fine.

josephlord 14y ago
Many computing problems can't be parallelised and in almost all there are dependencies and synchronisation issues that mean a single double speed CPU is almost always better than two normal ones. Exception might be that when a buggy programme gets locked in a tight loop it will only be able to take half the resources. To use another car analogy. Counting clock speed is like counting the cars max RPM instead of actually measuring the performance. And then they have totalled the max RPM figures as if they have have 90,000RPM engine.
- alexchamberlain 14y ago
  Conversely, there are many problems, most notably in the low-level mathematics, which can be parallelised. Matrix multiplication for example...
  - josephlord 14y ago
    Yes there are infinitely* many problems that can be parallelised but even in the best case they will only equal the single processor at double the speed. http://home.wlu.edu/~whaleyt/classes/parallel/topics/amdahl.html http://home.wlu.edu/~whaleyt/classes/parallel/topics/amdahl.... I should have referenced Amdahl's law in the previous post but didn't want to misspell it and bother to look it up. *Infinite numbers exist of both parallel and serial computing requirements. Practically there will almost always be additional cost in parallel implementation even if the extra is insignificant such as higher start up cost and coordination for shutdown.
    - mclarkk 14y ago
      Amdahl's Law did throw a damp cloth over the fire of enthusiasm about parallel computing...for a while. But then we got Gustafson's Law: http://en.wikipedia.org/wiki/Gustafson%27s_Law http://en.wikipedia.org/wiki/Gustafson%27s_Law Gustafson and Barsis pointed out that Amdahl assumed a fixed input size. If instead you grow the problem size along with the number of processors, the speedup from parallelism grows indefinitely. Of course, like Amdahl, they assume perfect load balancing and don't factor in communication overhead. But parallel still beats the pants off of serial if we want to keep solving larger and larger problems.
danbee 14y ago
Actually it can. If you have 16 people to move and 1 car that seats 4 it will take 4 round trips. 4 cars will do it in 1 one way trip. People = threads and cars = cores.
laumars 14y ago
You missed his point. Clock frequencies cannot be combined as it's a measure of the frequency a single core operates at - not how many operations per second can be processed. This is why multi-core CPUs don't say 8GHz even though they have 4x 2GHz cores.
- abcd_f 14y ago
  Of course I haven't missed the point. You did :) You can nitpick as much as you want, but for a lot of applications it's perfectly OK to sum up the frequencies. A job that can be spread over 8 cores will be executed at about the same time as it would execute on a single core at 8x the frequency
  - laumars 14y ago
    No it wouldn't. You have overhead generated by running threads concurrently (eg thread management, communication between nodes, etc). You have issues where not all threads are going to have the exact same complexity (eg some might consist of more floating point calculations than others), this could even result in threads sitting idle while they wait for another thread on a different core to finish. Plus there's absolutely no precedence for using clock frequencies cumulatively like this anyway (which I've already demonstrated with my multi-core CPU example), thus the figures Adapteva are touting are not only scientifically and mathematically inaccurate, but also breaking established advertising convention too. Thus their figures are incorrect - period. So accusing us of nitpicking incorrect figures is just plain dumb when there's absolutely no merit to the 13GHz figure what-so-ever. [edit] And it's a sad day for geeks worldwide if discussing the correct usage for scientific measurements is considered nitpicking. Had this been Fox News or the Daily Mail, then your view point could be forgiven. But this is a hacker forum, so I'd expect a higher level of technicality rather than simply ignoring counterarguments in such a dismissive manner. :(
    - abcd_f 14y ago
      Describing a gadget in terms of cumulative frequency of its cores is an A-Ok method of giving approximate performance, especially when it's obvious that it's a sum of cores. You and I and anyone moderately interested by this project know exactly what this number means. It is also pretty clear that they haven't meant to mislead or trick someone into thinking that they are building a 1THz computer for $99. So, yeah, it's nitpicking. A better angle would be - given the project and its goals, do you really think it's worth putting them down for something as trivial (and technically correct) as this - Once completed, the Parallella computer should deliver up to 45 GHz of equivalent CPU performance That, as they say on TechCrunch, is a dick move. If anything, they deserve a pat on a back and a donation.