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

[Rui Ueyama via llvm-commits]

For LLD, it hashed 75,421,320 bytes. For Scylla, it hashed 207,703,010
bytes. So the throughput of MD5 is 444 MB/s and 480 MB/s, respectively.

BLAKE2 claims that it is about 1.6x faster than MD5, but it is probably the
lower bound for a secure hash function.

On Thu, Mar 10, 2016 at 2:16 PM, Sean Silva <chisophugis at gmail.com> wrote:

> 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
>
>
>
>
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