Memory footprint (allocations)

[vvb333007]

Great job!

Did you measure PSRAM usage? E.g. how much takes one medium-size script, compiled?
How many compiled scripts can be executed simultaneously?

Did you measure memory usage during script execution?

Did you measure the tight loops speed? I.e. setting GPIO in a loop - what maximum gpio switch frequency can be achieved?

[GianfriAur]

hi @vvb333007

These are exactly the right questions to ask at, so let's say what I know cold vs. what I still need to put a.

First, a clarification on the execution model, because it reframes a couple of these. There's one interpreter, single-threaded. Two modes:

• Linear (setup() / loop()): one script, running start-to-finish or in a C-driven loop.
• Web-server: each HTTP request runs a fresh PHP request cycle — compile (or fetch from opcache) → execute → tear down. So scripts don't sit resident "in parallel"; there's always ~one executing at a time, and opcache is what keeps many compiled scripts cached between requests. So shortly 1

as for the other points:

• PSRAM per compiled script — architecturally, the whole Zend heap lives in PSRAM (USE_ZEND_ALLOC=0), so a compiled script = its op_arrays + interned strings on that heap. I have the static engine footprint documented footprint.md, based on the parts you put in the engine you can calculate it in a rough way, the only point that esp-idf then further completes it, to date it has not yet measured this data.
• Memory usage at runtime: They don't have a per-workload table yet, I still need to find a smart way to calculate it, but that being said 8Mb is enough to handle quite a few things and with 32Mb you can run a framework like symfony without it running out
• Tight-loop GPIO frequency: Each gpio_write() is an opcode dispatch + a C call to the IDF GPIO API, with the loop handing over control to the watchdog. So a pure PHP switching cycle will be on the order of kHz, not MHz: but I haven't actually measured it yet. For really fast or timing-critical signals, the right tool is a small C project extension (the firmware supports custom C project extensions) or a hardware peripheral (RMT/LEDC/I2S) managed by PHP. That said, it's already in the pipeline to create custom exts so that they can be implemented on the server. Generally, you use gpio_write on a relay, or to play with more serious protocols, you use exts but control them from PHP.

Furthermore, both the P4 and S3 support multi-core processing; I am not currently utilizing this—not because I haven't considered it, but because it is a somewhat delicate task. I am already implementing this for the event-driven mode, which naturally uses all cores to handle multiple tasks in parallel, so both of the aforementioned modes will support it in the future.

If you have any doubts, questions or difficulties in managing, please write, I will be happy to answer you, furthermore if you have any suggestions they are absolutely welcome ❤️

[GianfriAur]

hi @vvb333007

I put together a benchmark to test the aspects that you asked

You can find the benchmark here: examples/benchmark

After thinking about it for a long time and doing a couple of tests I ask that this is a correct and reliable way to observe this data

Since I saw that you work with esp32, if you have any suggestions/corrections/advice, let me know.

I'll bring you the report below:

	ESP32-S3 minimal board ("supermini")	ESP32-S3	ESP32-P4
PSRAM	2 MB Quad @ 80 MHz	8 MB Octal @ 80 MHz	32 MB @ 200 MHz
CPU	160 MHz (Xtensa)	160 MHz (Xtensa)	360 MHz (RISC-V)
engine baseline (PSRAM used)	~1.3 MB	~1.3 MB	~1.3 MB
free for your data	~0.7 MB	~6.9 MB	~31.5 MB
compile bench_small (17 ln / 0.4 KB)	2.3 KB	2.3 KB	2.3 KB
compile bench_medium (76 ln / 2.0 KB)	10.3 KB	10.3 KB	10.3 KB
compile bench_large (167 ln / 4.2 KB)	22.4 KB	22.4 KB	22.4 KB
GPIO — PHP loop	~155 kHz (3229 ns/write)	~155 kHz (3229 ns)	~279 kHz (1810 ns)
GPIO — C ext (native_gpio)	~1.4 MHz (357 ns)	~1.4 MHz (357 ns)	~1.35 MHz (371 ns)
C-over-PHP speedup	9×	9×	5×
5000-row working set (~1.83 MB)	doesn't fit → ~1091 rows / 0.4 MB	1.83 MB	1.83 MB

Let me know if you think there are other things that should be monitored

[vvb333007]

Thank you for elaborate testing and report!
Wish you luck with your project :).