Question

Continuing the discussion from Understanding VS2010 C# parallel profiling results but more to the point:

I have many threads that work in parallel (using Parallel.For/Each), which use many memory allocations for small classes.

This creates a contention on the global memory allocator thread.

Is there a way to instruct .NET to preallocate a memory pool for each thread and do all allocations from this pool?

Currently my solution is my own implementation of memory pools (globally allocated arrays of object of type T, which are recycled among the threads) which helps a lot but is not efficient because:

1. I can’t instruct .NET to allocate from a specific memory slice.
2. I still need to call new many times to allocate the memory for the pools.

Thanks,
Haggai

Answer 1

I searched for two days trying to find an answer to the same issue you had. The answer is you need to set the garbage collection mode to Server mode. By default, garbage collection mode set to Workstation mode.
Setting garbage collection to Server mode causes the managed heap to split into separately managed sections, one-per CPU.
To do this, you need to add a config setting to your app.config file.

<runtime>
   <gcServer enabled="true"/>
</runtime>

The speed difference on my 12-core Opteron 6172 was dramatic!