[MaxBarraclough]

To be clear, your program ran at half speed, right? That's far worse than doubling the time spent in memory-management functions.

[danlark]

Yes, our program ran at half speed.

[vinay_ys]

It is quite bad if changing the allocator made your program run at half speed. It doesn't matter if the library itself consumed more CPU or caused more wait (guessing that's the case here) due to concurrency or excessive syscalls.