RFR: 8257074 Update the ByteBuffers micro benchmark [v3]

[Maurizio Cimadamore]

On Thu, 26 Nov 2020 14:38:17 GMT, Chris Hegarty <chegar at openjdk.org> wrote:

>> The ByteBuffers micro benchmark seems to be a little dated. 
>> 
>> It should be a useful resource to leverage when analysing the performance impact of any potential implementation changes in the byte buffer classes. More specifically, the impact of such changes on the performance of sharp memory access operations. 
>> 
>> This issue proposes to update the benchmark in the following ways to meet the aforementioned use-case: 
>> 
>> 1. Remove allocation from the individual benchmarks - it just creates noise. 
>> 2. Consolidate per-thread shared heap and direct buffers. 
>> 3. All scenarios now use absolute memory access operations - so no state of the shared buffers is considered. 
>> 4. Provide more reasonable default fork, warmup, etc, out-of-the-box. 
>> 5. There seems to have been an existing bug in the test where the size parameter was not always considered - this is now fixed.
>
> Chris Hegarty has updated the pull request incrementally with one additional commit since the last revision:
> 
>   whitespace

Looks a great improvements. Two comments:

* the names always mention the "Single" word, when in fact all benchmark involve some kind of a loop. I'd suggest making that more  explicit, both in the benchmark method and in the helpers.

* I see that you added  support for views - but note that, for heap buffers there are two different kind of views (!!). E.g. I believe that:

ByteBuffer.allocate(size * 4).asFloatBuffer()
returns a buffer of a different class than:

FloatBuffer.allocate(size);
I think you are only testing the former?

-------------

PR: https://git.openjdk.java.net/jdk/pull/1430