fdcavalcanti opened a new pull request, #17969:
URL: https://github.com/apache/nuttx/pull/17969
- sched/sched_roundrobin.c: fix round-robin scheduling in SMP mode
In SMP mode, running tasks are in g_assignedtasks[cpu], not the ready-to-run
list, so tcb->flink is NULL. When a round-robin timeslice expires, checking
tcb->flink fails to find the next task.
Fix by calling nxsched_switch_running() directly in SMP mode when the
timeslice expires, which properly finds the next eligible task from the
ready-to-run list.
## Summary
This fixes #17828 and ESP32 `ostest` errors on `rr_test`.
In NuttX SMP, when a round-robin task’s timeslice expires, the code tried to
find the next task by checking `tcb->flink` (the next task in the ready-to-run
list). In SMP, running tasks are stored in `g_assignedtasks[cpu]`, not in the
ready-to-run list, so `tcb->flink` is NULL. This prevented finding the next
task and caused the round-robin test to fail.
### Fixing
Instead of checking `tcb->flink`, we call `nxsched_switch_running()`
directly. This function:
- Looks in the ready-to-run list for the next eligible task
- Handles SMP-specific logic
- Returns true if a switch should occur
### Main changes
Before (broken):
```c
if (tcb->flink && tcb->flink->sched_priority >= tcb->sched_priority)
{
// Switch to next task
}
```
This failed because `tcb->flink` was NULL in SMP mode.
After (fixed):
```c
else if (nxsched_switch_running(tcb->cpu, true))
{
up_switch_context(this_task(), rtcb);
}
```
This directly uses the scheduler function that knows how to find the next
task in SMP mode.
## Impact
Impact on user: Round-robin scheduling (SCHED_RR) works correctly in SMP
mode. Applications using round-robin scheduling will now properly alternate
between tasks of the same priority.
<!-- Does it impact user's applications? How? -->
Impact on build: No.
<!-- Does it impact on building NuttX? How? (please describe the required
changes on the build system) -->
Impact on hardware: Only affects SMP-capable hardware. No hardware changes
required.
<!-- Does it impact a specific hardware supported by NuttX? -->
Impact on documentation: No.
<!-- Does it impact the existing documentation? Please provide additional
documentation to reflect that -->
Impact on security: No.
<!-- Does it impact NuttX's security? -->
Impact on compatibility: No.
<!-- Does it impact compatibility between previous and current versions? Is
this a breaking change? -->
## Testing
`ostest` is passing on SMP ESP32 and ESP32S3.
Internal CI shows no errors regarding scheduler.
Fixes issues on network when SMP is enabled (getting stuck on downloads).
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