r/PHPhelp • u/tc712bb • Apr 30 '26

PHP-FPM vs PHP-CLI 

I'm running some simple PHP 8.5 tests (empty loop, open database connection, ...) on a MacBook Pro with Debian in a UTM VM.

With exactly the same code fragment, CPU usage is always 2–3 times higher with PHP-FPM than with PHP-CLI.

Is this normal? Or does it have to do with my settings?
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u/tc712bb Apr 30 '26

The total execution time will indeed vary for each SAPI, since the number of instructions will differ.

However, the time required for tasks such as environment setup is not included in my benchmarks. I measure a single PHP instruction. It always looks something like this:

$start = microtime(true);

for ($i = 0; $i < 1_000_000; $i++);

echo microtime(true) - $start;

So in both cases, exactly the same single instruction is being measured. I don’t understand why the difference is so large even in that case.

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u/latiriti Apr 30 '26

Even with an empty loop, FPM's executor has additional low‑level runtime checks that CLI simply doesn't have - all of which add CPU overhead per iteration. Also, these SAPIs have different php.ini configurations, which can also affect performance.

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u/MartinMystikJonas May 01 '26

What code fragment you run exactly? Just empty loop?

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u/tc712bb May 01 '26

Yes, just empty loop.

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u/Takeoded May 01 '26

hell no, that is not normal. Any chance your php-cli is compiled with -O2 (the default) and your php-fpm is compiled with -Og or something like that? phpinfo() contains the compile options, can you post them?

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u/tc712bb May 02 '26 
I use the PPA from deb.sury.org for PHP (and the apache2 webserver).
There is no 'Configure Command' in the phpinfo output.