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Author Topic: Multiple Cores, and the Wiki?  (Read 2871 times)

Jerm

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Multiple Cores, and the Wiki?
« on: September 17, 2009, 06:29:25 pm »

I'm sure its been asked and answered, but I'm hoping someone might help me out.

I've got a quad core AMD processor, and I'm wondering if DF works fine with all four cores, or if I should attune it to one or two..?

Also, anyone know what's up with the Wiki?  I get some hits when I google it, but the site doesn't seem to work.

Thanks!
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Holy Mittens

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Re: Multiple Cores, and the Wiki?
« Reply #1 on: September 17, 2009, 06:31:04 pm »

Df is not multithreaded, so it only ever uses one core.

Jay

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Re: Multiple Cores, and the Wiki?
« Reply #2 on: September 17, 2009, 06:52:53 pm »

Wiki recently changed hosts.  If it's not working, clear your DNS cache.
http://www.dwarffortresswiki.net/index.php/Main_Page
« Last Edit: September 17, 2009, 06:55:42 pm by jaybud4 »
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zchris13

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Re: Multiple Cores, and the Wiki?
« Reply #3 on: September 17, 2009, 06:59:45 pm »

Windows does this automatically as part of the "Repair network" function.
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Andir

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Re: Multiple Cores, and the Wiki?
« Reply #4 on: September 17, 2009, 10:16:19 pm »

Df is not multithreaded, so it only ever uses one core.
Well, technically I'm pretty sure the latest 40d## uses at least 2 (graphics)... but the main core is single threaded, so yeah.  Essentially, it will eat up 1.0421 (rough estimate) cores while it's running and the others will get cold and lonely.
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Neruz

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Re: Multiple Cores, and the Wiki?
« Reply #5 on: September 17, 2009, 10:44:35 pm »

Actually your OS will automagically swap it from core to core as the cores heat up to try and average out the load and keep the cores cool.

Thndr

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Re: Multiple Cores, and the Wiki?
« Reply #6 on: September 18, 2009, 02:28:08 am »

Actually your OS will automagically swap it from core to core as the cores heat up to try and average out the load and keep the cores cool.
Semantics.

The layman's answer is: Quad core, single core, DF is going to run basically the same.
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tomato

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Re: Multiple Cores, and the Wiki?
« Reply #7 on: September 18, 2009, 06:20:43 am »

Actually your OS will automagically swap it from core to core as the cores heat up to try and average out the load and keep the cores cool.
that's not clever in any way

by swapping process from core to core Windows introduces unnecessery cache misses and context switches ─ making the computer run slower

the difference is small (around 1-2% of performance), but limiting the process to single core will make it run faster on windows
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Draco18s

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Re: Multiple Cores, and the Wiki?
« Reply #8 on: September 18, 2009, 12:10:32 pm »

Actually your OS will automagically swap it from core to core as the cores heat up to try and average out the load and keep the cores cool.

Or you can buy a bigger fan.  May I suggest this one?

That fan took my machine--which with the stock fan ran at about 40C in the BIOS and pulled it down to heating up to a mere 43C after four hours of running Second Life (and 28C at idle).
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tefalo

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Re: Multiple Cores, and the Wiki?
« Reply #9 on: September 18, 2009, 12:35:31 pm »

Quote
Or you can buy a bigger fan cpu cooler.

Corrected for great justice/un-strangeness.

...But really, it's not just a fan. :P
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Draco18s

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Re: Multiple Cores, and the Wiki?
« Reply #10 on: September 18, 2009, 02:58:35 pm »

Quote
Or you can buy a bigger fan cpu cooler.

Corrected for great justice/un-strangeness.

...But really, it's not just a fan. :P

True.
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phalantas

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Re: Multiple Cores, and the Wiki?
« Reply #11 on: September 18, 2009, 04:40:22 pm »

better yet, use all 4 cores to simulate a single one. not sure how it is done, but I know it is possible
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Andir

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Re: Multiple Cores, and the Wiki?
« Reply #12 on: September 18, 2009, 04:53:02 pm »

better yet, use all 4 cores to simulate a single one. not sure how it is done, but I know it is possible
The only thing I've read recently about that being possible is something called "Reverse hyper threading" and that's not possible... at least not yet.  http://arstechnica.com/old/content/2006/07/7263.ars

Also, it was an April Fools joke: http://www.ngohq.com/news/15678-reverse-hyperthreading-wrapper-v0-1-a.html
« Last Edit: September 18, 2009, 04:55:49 pm by Andir »
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phalantas

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Re: Multiple Cores, and the Wiki?
« Reply #13 on: September 18, 2009, 05:26:27 pm »

hmm, could it have been single core processors that simulated multi core processors? I usually don't care too much about that kind of stuff, I just remember seeing some software at a friends computer
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Nadaka

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Re: Multiple Cores, and the Wiki?
« Reply #14 on: September 18, 2009, 09:18:20 pm »

better yet, use all 4 cores to simulate a single one. not sure how it is done, but I know it is possible

Not possible.
1: some problems are not parallelizable.
2: most code is not written to be run in parallel.
3: automatically converting code to run in parallel is a non-trivial task.
4: parallization is not free, spawning and disposing threads, synchronization, deadlock detection all take time, for threads of sufficiently small duration (those most easily identified) these costs outweigh the benefits gained.

Quote
hmm, could it have been single core processors that simulated multi core processors? I usually don't care too much about that kind of stuff, I just remember seeing some software at a friends computer

Not required. A single core can handle as many threads as a multi-core system can, its just that it can handle them only one at a time.


There are things that can be done to speed up a single process on multicore machines.
1: move all other threads to a different core, so that the single thread has full use without context switches.
2: (requires special hardware) run a nostore/noop predictive thread on the other cores to prefetch data from memory to cache. This reduces the latency involved in waiting to retrieve data from memory.

At most, these would give a few percent increase in performance. But they will work marginally for preexisting software.

The only real way to deal with it is a: educate programmers to understand and use parallelization, and to provide tools and language features that make parallelization easier to use. And these solutions don't really impact preexisting software.
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