[Cuis-dev] Jitter source during benchmarks

[John M McIntosh]

Take a look at these two modifications

- Heartbeat 2ms→10ms: Smalltalk vmParameterAt: 26 put: 10
- Replace idle process: 50ms relinquish instead of 1ms

....
John M. McIntosh. Corporate Smalltalk Consulting Ltd https://www.linkedin.com/in/smalltalk

Sent from [Proton Mail](https://proton.me/mail/home) for iOS.

-------- Original Message --------
On Tuesday, 05/12/26 at 12:18 Nicolás Papagna Maldonado via Cuis-dev <cuis-dev at lists.cuis.st> wrote:

> Hi folks,
>
> I'm in the process of doing performance benchmarks of my Code Coverage tool for my thesis, and I've encountered something interesting while measuring the test execution times of the Aconcagua package.
>
> Observation:
> When running the Aconcagua test suite 150 times in a clean image, the execution times are not normally distributed. Instead, they fall into two distinct "modes":
>
> [image.png]
> A Base Mode (~6.28 ms): Representing roughly 72% of the iterations.
> A Spike Mode (~7.0 ms): Representing roughly 28% of the iterations.
>
> As the next plot shows, the spikes are not random; they seem to be kind-of deterministic (roughly every 4th iteration).
> I think these perturbations are visible because I'm taking very small measurements (~6.28 ms).
> [image.png]
>
> Question:
> I am trying to isolate whether this "heartbeat" is originating from within the Cuis image or the VM/OS layer (I'm thinking of VM timer/events, maybe UI timers?)
> Does anyone know what could be causing this?
> Are there any known events that run at this particular frequency?
>
> I repeated the experiment a couple of times and the perturbations are consistent (in terms of ms and frequency).
>
> Methodology:
>
> - Measurements were taken in batches of 50 test runs.
> - Each batch was run in a fresh image, waiting 2 minutes for the VM to stabilize Cuis code.
> - 10 warmup runs were done and discarded before measuring test run times.
> - Measurements were taken using Time primHighResClock and converted to ms using Time highResTimerTicksPerMillisecond.
> - VM stats were collected before and after measurements. A full GC was run before taking measurements.
> - No GC activity was observed while measuring the tests run (VM stats report no full nor incremental GCs).
> - The test suite was created and run from a workspace
>
> Cuis environment:
>
> - Cuis Smalltalk commit: https://github.com/Cuis-Smalltalk/Cuis-Smalltalk-Dev/commit/b221722348cc46ebb9f5d9f3a057a3f361aa3d55
> - Code Coverage commit: https://github.com/npapagna/cuis-code-coverage/commit/db19de02250a3fd50dfc4e0b4d0893b656e31e9b
> - Aconcagua commit: https://github.com/Cuis-Smalltalk/Measures/commit/05aa02aada64f7b64898a5e1452ae8fb76f79427
> Machine environment:
>
> - Model Name: MacBook Pro
> - Model Identifier: MacBookPro18,3
> - Model Number: MKGR3LL/A
> - Chip: Apple M1 Pro
> - Total Number of Cores: 8 (6 Performance and 2 Efficiency)
> - Memory: 16 GB
> - System Firmware Version: 13822.81.10
> - OS Loader Version: 13822.81.102
> - APPLE SSD AP0512R (NVMe, avg read 5671 MB/s, avg write 5670 MB/s)
> - macOs 26.3 (25D125)
> - A dedicated fresh profile was created for the benchmarks (indexing, time machine, screen lock/saver, display shutdown, bluetooth and wifi disabled).
>
> Thanks in advance,
> Nico PM
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