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Old 2004-04-21, 12:31   #1
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Smile Dual CPUs and Hyperthreading

Hi,

I'd like to join the hunt for Mersenne primes. I have a dual processor (2 x 2.8GHz) Linux system with the option of hyperthreading. If I switch on hyperthreading, I then have 4 "logical" CPUs (CPU0 - CPU3) as displayed via the "top" command.

In order fully to utilise the system so that it will process the workunit as quickly as possible, what command(s) should I use to run mprime, e.g.,

./mprime -A2 (2 physical processors)
./mprime -B2 (2 physical processors; and in the background)
./mprime -A4 (4 logical processors)
./mprime -B4 (4 logical processors; and in the background)
./mprime -B2 -A2, etc................or something else?

pAuL
 
Old 2004-04-21, 13:55   #2
PrimeCruncher
 
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There are some numbers on this in various threads in the Hardware forum. This is the most recent.
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Old 2004-04-21, 14:02   #3
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OK......................thanks!
 
Old 2004-06-19, 20:08   #4
Spinny
 
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Question P4 with HT, dual prime95 ???

I have a P4 3.0 with HT. The question is this: Do I need to install a separate prime95 [in another directory??] in order to take full advantage of my new proc. ?? [I've read that I can run 2 separate prime95 but it doesn't say how exactly]. Will they run 2 separate tests or will they work together. 10q.

Last fiddled with by Spinny on 2004-06-19 at 20:09
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Old 2004-06-19, 20:18   #5
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If you want to run 2 instances and run Windows of any flavor, install in different directories.

However, there is no advantage to run 2 .exes. 2 run slower than one because of the battling for Ram and thru-put.
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Old 2004-06-19, 20:49   #6
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The thing is that I've noticed only 50% proc usage [and I thought what a waste computing power [until today I had a P4 2,4 fsb 533]] and that is the main reason behind my decision 2 run 2 diff instances. 10x again.
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Old 2004-06-19, 23:04   #7
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You will not get a performance gain by running two different copies--but you can try just to get some timings. Then you would see the iteration time (in the Prime95 window) double.
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Old 2004-06-20, 01:18   #8
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Since HT is a virtual processor, you'll actually get a big hit in performance when you run two instances of Prime95. Each instance will run at half the speed of one. Here is a link on how to run two instances as a service. It's for a real dual processor system, but works for HT as well. Remember to se the affinity. http://www.mersenneforum.org/showthr...dual+processor

Last fiddled with by delta_t on 2004-06-20 at 01:19
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Old 2004-06-20, 15:34   #9
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Quote:
Originally Posted by Spinny
The thing is that I've noticed only 50% proc usage [and I thought what a waste computing power [until today I had a P4 2,4 fsb 533]] and that is the main reason behind my decision 2 run 2 diff instances. 10x again.
This is only because your operating system thinks there is 2 processors. Your actual CPU usage is 100% of the actual CPU. The virtual CPU is getting nothing so it shows 50% of both CPU's.

Remember the virtual CPU doesn't exist.
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Old 2004-09-16, 10:04   #10
RazorWolf
 
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Exclamation Prime95 runs on my CPU only 50% !

Hi there,

I just installed and run prime95. its running now the 40st test run. I can see that it uses just 50-51% of CPU! I guess that must be because of Hyperthreating (right?). So, how can I let it run 100% ? I hope I not have to disable that HT feature.

thanx

RazorWolf
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Old 2004-09-16, 10:43   #11
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Quote:
Originally Posted by RazorWolf
Hi there,

I just installed and run prime95. its running now the 40st test run. I can see that it uses just 50-51% of CPU! I guess that must be because of Hyperthreating (right?). So, how can I let it run 100% ? I hope I not have to disable that HT feature.

thanx

RazorWolf
You are right, it's the HT feature.

Try to disable it from the BIOS settings.

Luigi
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