Hope this is a valid post here, its a combination of C# issues and hardware.

I am benchmarking our server because we have found problems with the performance of our quant library (written in C#). I have simulated the same performance issues with some simple C# code- performing very heavy memory-usage.

The code below is in a function which is spawned from a threadpool, up to a maximum of 32 threads (because our server has 4x CPUs x 8 cores each).

This is all on .Net 3.5

The problem is that we are getting wildly differing performance. I run the below function 1000 times. The average time taken for the code to run could be, say, 3.5s, but the fastest will only be 1.2s and the slowest will be 7s- for the exact same function!

I have graphed the memory usage against the timings and there doesnt appear to be any correlation with the GC kicking in.

One thing I did notice is that when running in a single thread the timings are identical and there is no wild deviation. I have also tested CPU-bound algorithms and the timings are identical too. This has made us wonder if the memory bus just cannot cope.

I was wondering could this be another .net or C# problem, or is it something related to our hardware? Would this be the same experience if I had used C++, or Java?? We are using 4x Intel x7550 with 32GB ram. Is there any way around this problem in general?

Stopwatch watch = new Stopwatch();
watch.Start();
List<byte> list1 = new List<byte>();
List<byte> list2 = new List<byte>();
List<byte> list3 = new List<byte>();


int Size1 = 10000000;
int Size2 = 2 * Size1;
int Size3 = Size1;

for (int i = 0; i < Size1; i++)
{
    list1.Add(57);
}

for (int i = 0; i < Size2; i = i + 2)
{
    list2.Add(56);
}

for (int i = 0; i < Size3; i++)
{
    byte temp = list1.ElementAt(i);
    byte temp2 = list2.ElementAt(i);
    list3.Add(temp);
    list2[i] = temp;
    list1[i] = temp2;
}
watch.Stop();

(the code is just meant to stress out the memory)

I would include the threadpool code, but we used a non-standard threadpool library.

EDIT: I have reduced "size1" to 100000, which basically doesn't use much memory and I still get a lot of jitter. This suggests it's not the amount of memory being transferred, but the frequency of memory grabs?