[v2] New benchtest: pthread locks

[DJ Delorie]

Siddhesh Poyarekar <siddhesh@gotplt.org> writes:
>> +/* The point of this benchmark is to measure the overhead of an empty
>> +   critical section or a small critical section.  This is never going
>> +   to be indicative of real application performance.  Instead we are
>> +   trying to benchmark the effects of the compiler and the runtime
>> +   coupled with a particular set of hardware atomic operations.
>> +   The numbers from this benchmark should be taken with a massive gain
>> +   of salt and viewed through the eyes of expert reviewers.  */
>
> That is a great comment.  All benchmarks should have a goal set like
> this so that it is clear to whoever evaluates them that just getting
> better numbers in a specific benchmark is not good enough and one would
> have to evaluate why a certain set of results supports their optimisation.

IIRC Carlos provided that text in one of his internal pre-reviews, so
kudos to him.  The remainder of the comments are mine though.