Dual Xeon 5355

bgbeuning · 2015-11-14, 19:51

I have a couple of machines running prime95 and just added a
HP GL360 G5 with dual Xeon 5355 (1U server).

The lscpu command on Linux is saying 1 thread per core,
so I am pretty sure hyperthreading is disabled even though
it is HT capable.

prime95 got 4 assignments, but each Xeon has 4 cores
so it should be able to work on 8 assignments.
Why only 4 assignments?

I noticed both Xeon are considered 1 NUMA node.
So main memory could be a bottleneck.
(Cache sizes - L1i 32KB, L1d 32KB, L2 2 MB per core)

Thanks,

MattcAnderson · 2015-11-16, 14:32

Hi bgbeuning

Wecome to mersenneforum and thank you for participating in our project.

I am pretty sure that Prime95 is optimized to run without hyper-threading.

I am sure others in the group can speak with more authority.

Regards

Matt

fivemack · 2015-11-16, 15:23

Quote:

Originally Posted by bgbeuning

I have a couple of machines running prime95 and just added a
HP GL360 G5 with dual Xeon 5355 (1U server).

The lscpu command on Linux is saying 1 thread per core,
so I am pretty sure hyperthreading is disabled even though
it is HT capable.

prime95 got 4 assignments, but each Xeon has 4 cores
so it should be able to work on 8 assignments.
Why only 4 assignments?

My guess is that the part of the prime95 code that detects CPU types assumes that machines capable of hyperthreading have it turned on even when it's disabled in the BIOS. Try putting WorkerThreads=8 in your local.ini file?

Mark Rose · 2015-11-16, 15:24

That's correct, Matt. Prime95/mprime works faster with hyperthreading disabled.

Hyperthreading works by filling holes in the execution pipeline with instructions from a second thread. However, Prime95/mprime is written very efficiently, such that there are no holes if the memory can keep up. If memory can't keep up, hyperthreading won't fill the holes. Hyperthreading only gets in the way.

If Prime95/mprime is able to detect hyperthreading is enabled it will run on only half the virtual cores as there is no advantage to running two threads on the same core.

bgbeuning · 2015-11-17, 00:00

Quote:

Originally Posted by fivemack

Try putting WorkerThreads=8 in your local.ini file?

That did the trick.
In a couple of hours I will know if it is getting twice the work done or not.

Thanks!

TheJudger · 2015-11-17, 17:53

Hi,

Xeon X5355 is Core 2 family thus they don't have hyperthreading.

2015-11-14, 19:51	#1
bgbeuning Dec 2014 FF₁₆ Posts	Dual Xeon 5355 I have a couple of machines running prime95 and just added a HP GL360 G5 with dual Xeon 5355 (1U server). The lscpu command on Linux is saying 1 thread per core, so I am pretty sure hyperthreading is disabled even though it is HT capable. prime95 got 4 assignments, but each Xeon has 4 cores so it should be able to work on 8 assignments. Why only 4 assignments? I noticed both Xeon are considered 1 NUMA node. So main memory could be a bottleneck. (Cache sizes - L1i 32KB, L1d 32KB, L2 2 MB per core) Thanks,

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2015-11-16, 14:32	#2
MattcAnderson "Matthew Anderson" Dec 2010 Oregon, USA 801₁₀ Posts	Hi bgbeuning Wecome to mersenneforum and thank you for participating in our project. I am pretty sure that Prime95 is optimized to run without hyper-threading. I am sure others in the group can speak with more authority. Regards Matt

2015-11-16, 15:24	#4
Mark Rose "/X\(‘-‘)/X\" Jan 2013 2·5·293 Posts	That's correct, Matt. Prime95/mprime works faster with hyperthreading disabled. Hyperthreading works by filling holes in the execution pipeline with instructions from a second thread. However, Prime95/mprime is written very efficiently, such that there are no holes if the memory can keep up. If memory can't keep up, hyperthreading won't fill the holes. Hyperthreading only gets in the way. If Prime95/mprime is able to detect hyperthreading is enabled it will run on only half the virtual cores as there is no advantage to running two threads on the same core.

2015-11-17, 17:53	#6
TheJudger "Oliver" Mar 2005 Germany 11·101 Posts	Hi, Xeon X5355 is Core 2 family thus they don't have hyperthreading.