

HHVM versus PHP-FPM 5.4 vs. PHP-FPM 5.5: performance comparison - Mojah
http://mattiasgeniar.be/2014/08/07/hhvm-versus-php-fpm-5-4-and-5-5-performance-comparison/

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eudoxus
To get a more accurate benchmark you should probably do higher then a single
concurrent connection, and 100 requests.

That's why you only saw a single core being used. Because it can be different
optimizations between the different PHP VMs that have different outcomes with
lower concurency values.

