Single vs Dual channel memory

TObject · 2014-12-19, 22:43

I just run benchmarks with single channel vs dual channel memory. Here they are.
Xeon E3-1225 v3, 3.20 GHz, LL Test on a 36M exponent.

Single channel:
4 workers: 6.5 ms/iter
3 workers: 6.4 ms/iter
2 workers: 6.8 ms/iter
1 worker: 10.0 ms/iter

Dual channel:
4 workers: 3.2 ms/iter
3 workers: 3.5 ms/iter
2 workers: 5.0 ms/iter
1 worker: 9.2 ms/iter

TheMawn · 2014-12-20, 01:21

This is no surprise. Prime95 is memory bottlenecked so the dual channel giving doubled memory bandwidth is huge.

Interestingly enough, the bottleneck only shows itself with more workers. A single one isn't enough to bottleneck you.

Note that the throughput is almost EXACTLY double with four workers with double the bandwidth, but even at 3 workers, there's a slight discrepancy. It means that your fourth worker, at those speeds, isn't actually giving you much more throughput.

LaurV · 2014-12-20, 06:53

Quote:

Originally Posted by TObject

workers

decreasing the time with increasing the number of workers sounds odd, unless you confuse the workers with the threads (single worker, working the same number with many cores).

TObject · 2014-12-20, 20:14

Quote:

Originally Posted by LaurV

decreasing the time with increasing the number of workers sounds odd, unless you confuse the workers with the threads (single worker, working the same number with many cores).

I am sorry for using wrong terminology, you are right. Instead of "workers" please read "threads."

Thank you.

TObject · 2014-12-23, 23:18

The numbers above were taken running mprime under Ubuntu 14.04 bare metal.
I decided to measure how much I would lose by virtualizing Ubuntu under ESXi 5.5. To my surprise–not that much: with no other virtual machines running, I am only losing about 0.05 of a millisecond per iteration.

I am impressed. I was expecting a much larger penalty.

LaurV · 2014-12-24, 05:58

Interesting, virtualizing windows with Oracle/Sun's VBox and running P95 in the guest windoze (of course, the host system doing nothing) loses over 2-3% of performance! (of course, in practice this will never be done, but for the sake of metrics).

2014-12-19, 22:43	#1
TObject Feb 2012 195₁₆ Posts	Single vs Dual channel memory I just run benchmarks with single channel vs dual channel memory. Here they are. Xeon E3-1225 v3, 3.20 GHz, LL Test on a 36M exponent. Single channel: 4 workers: 6.5 ms/iter 3 workers: 6.4 ms/iter 2 workers: 6.8 ms/iter 1 worker: 10.0 ms/iter Dual channel: 4 workers: 3.2 ms/iter 3 workers: 3.5 ms/iter 2 workers: 5.0 ms/iter 1 worker: 9.2 ms/iter

2014-12-23, 23:18	#5
TObject Feb 2012 3⁴×5 Posts	Another interesting metric. The numbers above were taken running mprime under Ubuntu 14.04 bare metal. I decided to measure how much I would lose by virtualizing Ubuntu under ESXi 5.5. To my surprise–not that much: with no other virtual machines running, I am only losing about 0.05 of a millisecond per iteration. I am impressed. I was expecting a much larger penalty.

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2014-12-20, 01:21	#2
TheMawn May 2013 East. Always East. 11×157 Posts	This is no surprise. Prime95 is memory bottlenecked so the dual channel giving doubled memory bandwidth is huge. Interestingly enough, the bottleneck only shows itself with more workers. A single one isn't enough to bottleneck you. Note that the throughput is almost EXACTLY double with four workers with double the bandwidth, but even at 3 workers, there's a slight discrepancy. It means that your fourth worker, at those speeds, isn't actually giving you much more throughput.

2014-12-24, 05:58	#6
LaurV Romulan Interpreter "name field" Jun 2011 Thailand 3×23×149 Posts	Interesting, virtualizing windows with Oracle/Sun's VBox and running P95 in the guest windoze (of course, the host system doing nothing) loses over 2-3% of performance! (of course, in practice this will never be done, but for the sake of metrics).