The order did switch a little between runs, but that largely ceased once I stopped fiddling about with other processes while the benchmarks were running. I get the same for a locale using a dot as the decimal separator (same WSL system and perl, and also for Strawberry perl 5.28.1). I'll have to try on a native linux machine.

I'm not sure why your results are so different. The results I showed use a de_DE locale, so perhaps there is overhead when locale handling is triggered. There are also noise effects with benchmarking, although the numbers are pretty distinct in this case. It could also just be my system.

As for use strict and use warnings, I've been bitten before with string based benchmarking when trying to avoid sub overheads. Taking them out makes no difference to the results (see below, although there is one case where y is faster than s).

The underlying benchmark code actually calls no strict before it evals code passed as strings. Note the _doeval call in the code generation when a string is passed.

Results without strict and warnings:

de_DE.iso88591
3,1
3.1
3.1
                Rate y_sprintf s_sprintf   sprintf
y_sprintf  4515837/s        --      -34%      -67%
s_sprintf  6804054/s       51%        --      -50%
sprintf   13639660/s      202%      100%        --
                Rate s_sprintf y_sprintf   sprintf
s_sprintf  4065578/s        --      -14%      -64%
y_sprintf  4737930/s       17%        --      -58%
sprintf   11298563/s      178%      138%        --
                Rate y_sprintf s_sprintf   sprintf
y_sprintf  4822333/s        --      -36%      -61%
s_sprintf  7501079/s       56%        --      -39%
sprintf   12255085/s      154%       63%        --
                Rate y_sprintf s_sprintf   sprintf
y_sprintf  4712721/s        --      -40%      -65%
s_sprintf  7853825/s       67%        --      -42%
sprintf   13493133/s      186%       72%        --
                Rate y_sprintf s_sprintf   sprintf
y_sprintf  4521907/s        --      -33%      -66%
s_sprintf  6739662/s       49%        --      -50%
sprintf   13393012/s      196%       99%        --
                Rate y_sprintf s_sprintf   sprintf
y_sprintf  4736894/s        --      -37%      -58%
s_sprintf  7546779/s       59%        --      -34%
sprintf   11352494/s      140%       50%        --
                Rate y_sprintf s_sprintf   sprintf
y_sprintf  4954521/s        --       -9%      -68%
s_sprintf  5458237/s       10%        --      -64%
sprintf   15366383/s      210%      182%        --
                Rate y_sprintf s_sprintf   sprintf
y_sprintf  4728476/s        --      -33%      -65%
s_sprintf  7101698/s       50%        --      -47%
sprintf   13504703/s      186%       90%        --
                Rate y_sprintf s_sprintf   sprintf
y_sprintf  4823862/s        --      -21%      -65%
s_sprintf  6083467/s       26%        --      -56%
sprintf   13732768/s      185%      126%        --
                Rate y_sprintf s_sprintf   sprintf
y_sprintf  4290706/s        --      -39%      -65%
s_sprintf  6993552/s       63%        --      -42%
sprintf   12119185/s      182%       73%        --
[download]