[PATCH] D18055: ELF: Implement --build-id.

[Sean Silva via llvm-commits]

silvas added a subscriber: silvas.
silvas added a comment.

One thing that is missing from the data you provided in the OP is the actual amount of data hashed, and in what pattern (lots of small, or a couple large?). How fast does the hashing have to be to be "acceptable"? E.g. ADT/Hashing.h claims 6.5GB/s hashing for large keys on Nehalem (which is pretty old at this point, modern CPU's likely to better). That is 6.5MB/ms. If we need to hash 100MB then the overhead should be about 15ms.

For LLD, you quoted a number 713.78ms link time. So for 1% overhead we need to spend <7ms. This is enough for 45MB hashed with ADT/Hashing.h (which is similar to LLD text+data size), assuming that we can get max memory bandwidth (like Rafael said, we can do this while we would be copying data otherwise, so I don't see a reason we can't hit the full performance of ADT/Hashing.h).


http://reviews.llvm.org/D18055