4 ms·

What to do with those idle cores?

11 points by wheels 18y ago

alexitosrv 18y ago
I would say to precompute anything the user could run to make things run faster, however accurate anticipation of user needs is really hard. I only thought of these tasks: In a word processing: we can load grammar and nlp engines and download and analyze trends in web text for improve suggestions in nearly real time, also trying to understand what the user is writing and aiding to improve not only orthography and grammar but style too, for example. In Web search, personalizing the whole searching and browsing experience downloading and processing partial results and with intelligent assistants running in the background (this is my favorite).
deleted 18y ago
[deleted]
comatose_kid 18y ago
Instead of doing more work with idle cores, why not spread the work out amongst them? This might provide a net savings in power consumption... Given that technologies like speedstep allow the voltage and frequency of a cpu to be modified dynamically, and that power consumption is governed by P = CV^2f: Say we have a CPU with 4 cores with each core equivalent to a 1.6 GHz Pentium M. According to Wikipedia, the clock frequency on such a device can be stepped in 200 MHz increments over the range from 1.6 to 0.6 GHz. At the same time, the voltage requirement decreases from 1.484 V to 0.956 V. So, say you have a workload that keeps one 1.6GHz core pegged to near 100%. Instead, why not spread this work to 3 cores, while lowering the speed to 0.6GHz and the voltage to 0.956V? This would be equivalent to a 1.8GHz machine. Would this save energy? The original power factor is: 1 core * (1.484^2) * 1.6 = 3.52 The new power factor is: 3 cores * (0.956^2) * 0.6 = 1.645 So, about half the power for this example. Of course, nothing is perfect, and spreading your workload amongst 3 cores will lose efficiency, and gain implementation complexity.
- jmtulloss 18y ago
  Of course spreading the work is a good idea, but most apps aren't built for multiple processors now, and unless they need to be, they won't be in the future. If an app is fast enough on one core, it won't be optimized for 8.
  - wheels 18y ago
    One thing that's interesting there is that toolkits are starting to contain elements to make parallelization easier. Qt specifically now has support via QtConcurrent for map and map-reduce patterns that are automatically farmed out to a threadpool the same size as the number of cores and it handles most of the hairy bits of doing threading. I've had to patch it heavily for my own use, but it's still a promising advance. I suspect we'll see more of the same in toolkits in the future.
- pmjordan 18y ago
  Another thing you're not taking into account is that on modern CPUs, execution units that aren't being used are put in low-power states. So in the simplest case, pure integer code uses less power than integer/floating-point code, and a core doing nothing at all goes into "deep sleep". A practical consequence of this appears on a modern Core2 laptop, if you have a computational task of fixed size and let it run, once with speedstep locked to the lowest level and once with dynamic clocks. Obviously the dynamically clocked one will finish more quickly and sit idle after that. If you let it sit idle until the low-clocked one has finished, you'll find the low-clocked one will have consumed more total energy. This means that for occasional-load scenarios, the dynamic clocking gives longer battery life, and for heavy load it gives shorter waits. Spreading does make sense even in this light of course, as things like shared caches, memory and bus controllers need to run as soon as at least one core is active.
- Andys 18y ago
  That would be a good idea for older chips like the Pentium M, but Intel's latest CPUs feature power gates so efficient that the current draw of an idle CPU that has been shut down, is very close to zero. Furthermore when all but one core is shut down, the clock speed of the remaining core can actually go UP by about 200mhz (called Turbo mode), providing a speed benefit to a single-threaded task.
signa11 18y ago
will it be possible to have processor cores reconfigured dynamically for efficient execution of task at hand ?
tophat02 18y ago
I'd say you make a business like Amazon EC2, Windows Azure, whatever, but you find a way to implement "virtual virtual machines" using the idle resources of millions of computers, but you couldn't pay each user enough to overcome the sudden rise in their electricity bills.

11 points by wheels 18y ago

I would say to precompute anything the user could run to make things run faster, however accurate anticipation of user needs is really hard. I only thought of these tasks: In a word processing: we can load grammar and nlp engines and download and analyze trends in web text for improve suggestions in nearly real time, also trying to understand what the user is writing and aiding to improve not only orthography and grammar but style too, for example. In Web search, personalizing the whole searching and browsing experience downloading and processing partial results and with intelligent assistants running in the background (this is my favorite).

deleted 18y ago

[deleted]

comatose_kid 18y ago

Instead of doing more work with idle cores, why not spread the work out amongst them? This might provide a net savings in power consumption... Given that technologies like speedstep allow the voltage and frequency of a cpu to be modified dynamically, and that power consumption is governed by P = CV^2f: Say we have a CPU with 4 cores with each core equivalent to a 1.6 GHz Pentium M. According to Wikipedia, the clock frequency on such a device can be stepped in 200 MHz increments over the range from 1.6 to 0.6 GHz. At the same time, the voltage requirement decreases from 1.484 V to 0.956 V. So, say you have a workload that keeps one 1.6GHz core pegged to near 100%. Instead, why not spread this work to 3 cores, while lowering the speed to 0.6GHz and the voltage to 0.956V? This would be equivalent to a 1.8GHz machine. Would this save energy? The original power factor is: 1 core * (1.484^2) * 1.6 = 3.52 The new power factor is: 3 cores * (0.956^2) * 0.6 = 1.645 So, about half the power for this example. Of course, nothing is perfect, and spreading your workload amongst 3 cores will lose efficiency, and gain implementation complexity.

jmtulloss 18y ago
Of course spreading the work is a good idea, but most apps aren't built for multiple processors now, and unless they need to be, they won't be in the future. If an app is fast enough on one core, it won't be optimized for 8.
- wheels 18y ago
  One thing that's interesting there is that toolkits are starting to contain elements to make parallelization easier. Qt specifically now has support via QtConcurrent for map and map-reduce patterns that are automatically farmed out to a threadpool the same size as the number of cores and it handles most of the hairy bits of doing threading. I've had to patch it heavily for my own use, but it's still a promising advance. I suspect we'll see more of the same in toolkits in the future.
pmjordan 18y ago
Another thing you're not taking into account is that on modern CPUs, execution units that aren't being used are put in low-power states. So in the simplest case, pure integer code uses less power than integer/floating-point code, and a core doing nothing at all goes into "deep sleep". A practical consequence of this appears on a modern Core2 laptop, if you have a computational task of fixed size and let it run, once with speedstep locked to the lowest level and once with dynamic clocks. Obviously the dynamically clocked one will finish more quickly and sit idle after that. If you let it sit idle until the low-clocked one has finished, you'll find the low-clocked one will have consumed more total energy. This means that for occasional-load scenarios, the dynamic clocking gives longer battery life, and for heavy load it gives shorter waits. Spreading does make sense even in this light of course, as things like shared caches, memory and bus controllers need to run as soon as at least one core is active.
Andys 18y ago
That would be a good idea for older chips like the Pentium M, but Intel's latest CPUs feature power gates so efficient that the current draw of an idle CPU that has been shut down, is very close to zero. Furthermore when all but one core is shut down, the clock speed of the remaining core can actually go UP by about 200mhz (called Turbo mode), providing a speed benefit to a single-threaded task.

signa11 18y ago

will it be possible to have processor cores reconfigured dynamically for efficient execution of task at hand ?

tophat02 18y ago

I'd say you make a business like Amazon EC2, Windows Azure, whatever, but you find a way to implement "virtual virtual machines" using the idle resources of millions of computers, but you couldn't pay each user enough to overcome the sudden rise in their electricity bills.