[PATCH] benchtests: New strlen-struct benchmark

[Siddhesh Poyarekar]

On 08/08/2018 09:13 PM, Wilco Dijkstra wrote:
> So my first question is, what are you trying to benchmark here?
> The strings are all identically sized so it won't stress strlen. The
> layout of the structs and strings is such that it ends up as one linear
> sweep of memory (which any prefetcher should be able to spot).
> Would better results on this test mean real code gets faster too?

Yeah, I added a larger padding in the struct to make the access stride a 
bit uneven, but I suspect some prefetchers may still be able to do 
something useful with it.  I played around with the string and list 
lengths to stabilize the benchmark numbers further, but I suppose stable 
numbers don't necessarily mean useful numbers.

> If you want to benchmark strlen in a more realistic way then it would
> make sense to do something like the random memcpy (create an
> array of strings based on a measured distribution and ensure the
> strings are not laid out linearly in memory).
> 
> If you have a specific workload you want to mimic then it may be
> better to keep it closer to the original code. Traversing a linked list of
> 10000 entries with 32KB strings seems quite unusual...

TBH I couldn't find any real workloads that use strlen that I could 
emulate, which is why I did this weird attempt at emulating list 
traversal.  I was trying to stay away from inventing my own size 
distribution because it becomes just another arbitrary data point that I 
won't even understand fully and it's also harder to stabilize the 
results; memcpy-random has that problem for example.

Do you have any specific ideas based on your experience with workloads 
that you've seen in the past?

Thanks,
Siddhesh