[RFC v2] eal: provide option to use compiler memcpy instead of RTE

[Mattias Rönnblom]

On 2024-05-28 09:43, Mattias Rönnblom wrote:
> Provide build option to have functions in <rte_memcpy.h> delegate to
> the standard compiler/libc memcpy(), instead of using the various
> traditional, handcrafted, per-architecture rte_memcpy()
> implementations.
> 
> A new meson build option 'use_cc_memcpy' is added. The default is
> true. It's not obvious what should be the default, but compiler
> memcpy() is enabled by default in this RFC so any tests run with this
> patch use the new approach.
> 
> One purpose of this RFC is to make it easy to evaluate the costs and
> benefits of a switch.
> 

I've tested this patch some with DSW micro benchmarks, and the result is 
a 2.5% reduction of the DSW+testapp overhead with cc/libc memcpy. GCC 11.4.

We've also run characteristic test suite of a large, real world app. 
Here, we saw no effect. GCC 10.5.

x86_64 in both cases (Skylake and Raptor Lake).

Last time we did the same, there were a noticeable performance 
degradation in both the above cases.

This is not a lot of data points, but I think it we should consider 
making the custom RTE memcpy() implementations optional in the next 
release, and if no-one complains, remove the implementations in the next 
release.

(Whether or not [or how long] to keep the wrapper API is another question.)

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