Proposal for hardware configuration dependent performance limits

[Sebastian Huber]

Hello,

there is one aspect with respect to performance limits which is 
currently not considered in this proposal:

https://lists.rtems.org/pipermail/devel/2020-November/063213.html

You can run the some BSPs such as sparc/gr712rc on several boards. 
However, each board may have different settings which affect the system 
performance, for example the CPU frequency, memory controller settings, 
memory chips, etc. In the proposal, limits are specified like this:


limits:
   sparc/gr712rc:
     DirtyCache:
       max-upper-bound: 0.000005
       mean-upper-bound: 0.000005
     FullCache:
       max-upper-bound: 0.000005
       mean-upper-bound: 0.000005
     HotCache:
       max-upper-bound: 0.000005
       mean-upper-bound: 0.000005
     Load/1:
       max-upper-bound: 0.00001
       mean-upper-bound: 0.00001
     Load/2:
       max-upper-bound: 0.00001
       mean-upper-bound: 0.00001
     Load/3:
       max-upper-bound: 0.00001
       mean-upper-bound: 0.00001
     Load/4:
       max-upper-bound: 0.00001
       mean-upper-bound: 0.00001

This neglects that the limits are subject to a board configuration. One 
approach to cover this is the addition of a new BSP provided function:

const char *rtems_get_hardware_performance_hash();

The BSP feeds all performance related data into a hash function and 
returns a string encoding (for example a MD5 digest in base64 encoding). 
The example from above with the performance hash:

limits:
   sparc/gr712rc/XrY7u+Ae7tCTyyK7j1rNww==:
     DirtyCache:
       max-upper-bound: 0.000005
       mean-upper-bound: 0.000005

The test suite could report the performance has and a test output analyser coudl check that the reported values are in the specified bounds.

-- 
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Sebastian HUBER
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