Dual CPUs and Hyperthreading

2004-04-21, 12:31

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

PrimeCruncher · 2004-04-21, 13:55

There are some numbers on this in various threads in the Hardware forum. This is the most recent.

2004-04-21, 14:02

OK......................thanks!

Spinny · 2004-06-19, 20:08

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.

outlnder · 2004-06-19, 20:18

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.

Spinny · 2004-06-19, 20:49

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.

patrik · 2004-06-19, 23:04

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.

delta_t · 2004-06-20, 01:18

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

outlnder · 2004-06-20, 15:34

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.

RazorWolf · 2004-09-16, 10:04

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

ET_ · 2004-09-16, 10:43

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

2004-04-21, 12:31	#1
Unregistered 2³·1,187 Posts	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

2004-06-19, 20:08	#4
Spinny Jun 2004 Bucharest 2₁₀ Posts	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

2004-06-20, 01:18	#8
delta_t Nov 2002 Anchorage, AK 3·7·17 Posts	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

2004-09-16, 10:04	#10
RazorWolf Sep 2004 3₁₆ Posts	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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2004-04-21, 13:55	#2
PrimeCruncher Sep 2003 Borg HQ, Delta Quadrant 702₁₀ Posts	There are some numbers on this in various threads in the Hardware forum. This is the most recent.

2004-04-21, 14:02	#3
Unregistered 2⁵×3×13 Posts	OK......................thanks!

2004-06-19, 20:18	#5
outlnder Aug 2002 2×3×53 Posts	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.

2004-06-19, 20:49	#6
Spinny Jun 2004 Bucharest 2 Posts	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.

2004-06-19, 23:04	#7
patrik "Patrik Johansson" Aug 2002 Uppsala, Sweden 5²×17 Posts	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.