guide/sidecar: expand docs on how openhcl boots #2542
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@jstarks , @chris-oo , @smalis-msft : interested in your reviews in particular. I hope I got it right, but could use your help to make sure my understanding is correct. |
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Pull request overview
This PR adds documentation to explain the OpenHCL sidecar boot process, specifically focusing on how the bootstrap processor (BSP) initializes the system and how application processors (APs) are started using a fan-out pattern. The documentation describes the concurrency management through atomic counters and page table setup for control page access.
Key Changes
- Added a "Processor Startup" section to the sidecar module documentation explaining the boot sequence
- Added a reference to a new documentation file in the Guide's SUMMARY.md
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| openhcl/sidecar/src/main.rs | Adds comprehensive documentation about the sidecar boot process, including BSP initialization, AP startup fan-out pattern, and control page mapping |
| Guide/src/SUMMARY.md | Adds a new entry for "Boot Process" documentation under OpenHCL Architecture section |
| //! | ||
| //! # Processor Startup | ||
| //! | ||
| //! The sidecar kernel is initialized by a single bootstrap processor (BSP), |
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Is this all true even with multiple numa nodes?
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Yes. I see your confusion and have updated the docs to better reflect this.
| The sidecar kernel: | ||
| - Runs independently on each CPU with minimal memory footprint | ||
| - Executes a simple dispatch loop, halting until needed | ||
| - Handles VP (virtual processor) run commands from the host VMM |
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Is this specific to the sidecar kernel? If not, what are some example commands that can be sent from the host VMM?
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Sorta. I'll try to address this once I get back to working on the Sidecar side of things. But this is the kind of stuff:
openvmm/openhcl/sidecar_client/src/lib.rs
Line 54 in 71608f1
| - Runs independently on each CPU with minimal memory footprint | ||
| - Executes a simple dispatch loop, halting until needed | ||
| - Handles VP (virtual processor) run commands from the host VMM | ||
| - Can be converted to a Linux CPU on demand if more complex processing is required |
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Are there some example scenarios that we can enumerate here?
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I left it brief, but all our IO handling happens per-CPU. The CPU needs to be a "Linux" CPU at that point. Think of sidecar as handling only VM exits, but not anything you'd expect to see in the openhcl bin.
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Thanks @smalis-msft and @damanm24 for the feedback! As I suspected, I've learned from your comments :) I'll incorporate them (though I may defer some of the additions to a later date). |
mattkur
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mattkur
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Thanks for the first round of feedback!
| - Runs independently on each CPU with minimal memory footprint | ||
| - Executes a simple dispatch loop, halting until needed | ||
| - Handles VP (virtual processor) run commands from the host VMM | ||
| - Can be converted to a Linux CPU on demand if more complex processing is required |
There was a problem hiding this comment.
I left it brief, but all our IO handling happens per-CPU. The CPU needs to be a "Linux" CPU at that point. Think of sidecar as handling only VM exits, but not anything you'd expect to see in the openhcl bin.
3 participants
Co-draft, with CoPilot, some additional documentation for the OpenHCL boot process and sidecar. I focused on some of the questions that I've recently had about how this stuff works.