Eventloop thread count not matching number of cores.

[Billy Yarosh]

Is there stronger documentation around how Vert.x determines the number of eventloop threads it starts? According to the docs it's one per CPU core. I am on an Intel i7 and am seeing 16 eventloop threads. I also notice that thread 0 is never used by any verticle. Why is that? My i7 claims to be 4 cores with 8 threads.

[Billy Yarosh]

I have reviewed the code and it looks like event loop thread are created with the algorithm: (2 * "available cores")

The source is in 2.x branch in VertxOptions

public static final int DEFAULT_EVENT_LOOP_POOL_SIZE = 2 * Runtime.getRuntime().availableProcessors();

In my case, my processor is 4 cores, but supports 8 thread. 8 is then what

Runtime.getRuntime().availableProcessors();

responds with.

  

Should the documentation be updated? 

[Tim Fox]

On 23/12/14 17:32, Billy Yarosh wrote:

I have reviewed the code and it looks like event loop thread are created with the algorithm: (2 * "available cores")

The source is in 2.x branch in VertxOptions

public static final int DEFAULT_EVENT_LOOP_POOL_SIZE = 2 * Runtime.getRuntime().availableProcessors();

Yes, we use 2 * number of cores by default - in practice this gives better results as OSes don't always distribute threads evenly across cores.

In my case, my processor is 4 cores, but supports 8 thread. 8 is then what

Runtime.getRuntime().availableProcessors();

responds with.

  

Should the documentation be updated?

Docs look ok to me :)

Note, it says " The default size is determined by the number of cores" not " The default size is equal to the number of cores"

I.e. it's a *function* of the number of cores N, f(N)

On Monday, December 22, 2014 1:39:26 PM UTC-5, Billy Yarosh wrote:

Is there stronger documentation around how Vert.x determines the number of eventloop threads it starts? According to the docs it's one per CPU core. I am on an Intel i7 and am seeing 16 eventloop threads. I also notice that thread 0 is never used by any verticle. Why is that? My i7 claims to be 4 cores with 8 threads.

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[Billy Yarosh]

I think the docs are clear enough. The threading model is key to understanding Vert.X, so my initial question was if there were more specific documentation. When reading the docs, I was assuming the algorithm was threads = CPU cores. I think the docs are fair in that the algorithm should be implementation specific, but leading towards the core count as the fixed algorithmic factor.

Thanks