snoyberg/conduit — comment on commit 369c2ff6966446a985b0d7d072150c515e86da13
File:  line 0
By meteficha:

Wheeww, I thought you were saying that `modifyMVar` was faster than `modifyIORef` =). I don't know how `MVar`s are internally implemented, but there must be a reason. And I don't see anything wrong with the test. If you wanted something even more complete, you could add a plain loop in IO summing something outside a reference using an accumulator, and a test using `TVar`s.

Note that if your test had multiple threads accessing *different* `IORef`s with `atomicModifyIORef`, I guess performance would suffer even more. (Accessing the same `IORef` would not be meaningful since on this case the primitives would be giving different guarantees.)

So there you go, another performance improvement. When will things stop getting better? =O =)