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[BUG] testing/sched/timerjitter: unexpected results under normal usage

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调研方向

首先定位 apps/testing/sched/timerjitter 入口点,并使用显示的参数在 QEMU RISC-V 上复现这三种情况:无参数、100 5 和 10000 10。跟踪迭代次数、丢失的帧以及 jitter 极值是如何计算和打印的。当报告的运行能够可靠完成、避免无效的 NaN 或回绕值,并保留有意义的延迟结果时,即视为完成。

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描述

Type: Bug
Description / Steps to reproduce the issue

Found while testing apps/testing/sched/timerjitter on QEMU RISC-V (rv-virt), NuttX-13.0.0-RC2. All three reproduce under normal, non-adversarial usage. A separate off-by-one in the sample loop was already
fixed in pull#3629

  1. avg: nan with default args
  nsh> timerjitter
  timer jitter in 0 run:
  (latency/us) min: 4294967295, avg: nan, max 0

Running with no arguments at all completes 0 iterations and prints avg: nan. Should the default guarantee at least 1 iteration, or otherwise avoid printing nan?

  1. Very large missed-frame counts, one run did not finish
  nsh> timerjitter 100 5
  time frame missed 1
  ...
  time frame missed 17363
  timer jitter in 5 run:
  (latency/us) min: 3129, avg: 347295, max 1269743

Another run with the same arguments printed missed-frame lines continuously and never completed; it had to be terminated externally:

  nsh> timerjitter 100 5
  time frame missed 1
  ...
  time frame missQEMU: Terminated
  1. Negative jitter shown as a huge unsigned value
  nsh> timerjitter 10000 10
  time frame missed 1
  timer jitter in 10 run:
  (latency/us) min: 4294966445, avg: 1010, max 12854

4294966445 = 2^32 - 851. avg in the same run is a small, plausible number, while min is not — suggesting min/max end up holding a negative value that gets displayed as a large unsigned one.

On which OS does this issue occur?

[OS: Linux]

What is the version of your OS?

Ubuntu 20.04

NuttX Version

master

Issue Architecture

[Arch: all]

Issue Area

[Area: Testing]

Host information

Environment

  • Board/config: boards/risc-v/qemu-rv/rv-virt/configs/knsh_romfs, running on QEMU
  • CONFIG_USEC_PER_TICK changed from the board's default (1000) back to the Kconfig default 10000
Verification
  • I have verified before submitting the report.
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