Q: Given a 32-core machine and a lot of CPU-bound calculations, how would you size your thread pool?

A: First, find out how many kernel threads -- probably 32 * 2 or 4. i feel if tasks are IO intensive like waiting for a pricing or risk assessment from JMS, then a lot of threads would be waiting for IO. If each thread spends 90% of its time waiting for IO, then each cpu should handle 10 threads roughly. This way, each thread after getting the data needed won't need to wait to get CPU.

The below questions were probably not prepared in advance.

Q1: for a one-direction linked list of size N, efficiently find the item at Position floor(N/2). Positions are 1 to N. You don't know the size until you finish scanning.

Q2: for a strictly sorted binary tree of numbers, I give you a pointer to the root node and 2 arbitrary numbers in the tree, find the lowest common ancestor node. The only entry point is the root node address. The 2 input numbers are passed by value and guaranteed to exist in the tree. Note for this binary tree, any node on my left are less than me.

Q3: efficiently reshuffle a PokerCard[52] array. You can call a rand(int max) function to get a random number between 0 and max.

Tip: avoid "retry" as that wastes CPU

A: i think we need to call rand(51), rand(50), rand(49)....

## Wednesday, March 31, 2010

### DMA low latency interview (European bank Midtown

Labels: thread, tuneLatency, z_MOM

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