关于f-stack在bbr上的一个bug

[qq16496578]

最近在测试我公司的25g网卡时，发现了一个f-stack bbr的bug，是一个传参的问题，因为这个问题在使用bbr算法时，性能一直上不去。

bbr_get_raw_target_cwnd(bbr, gain, bw)此函数定义与被调用时传参的顺序不一致。应改为bbr_get_raw_target_cwnd(bbr, bw, gain)

如已发现此bug，可忽略。

[jfb8856606]

Thank you for your testing and feedback.

We checked the definition and usage of the function and it does appear to have an issue.

We further examined the FreeBSD-release-13.0 branch code used by F-Stack, as well as the code of the upcoming FreeBSD release-15.0 branch, and found that there have been no modifications.

We will conduct some further testing and provide feedback later, but it may take a considerable amount of time before we can proceed.

[jfb8856606]

We have confirmed the bug and submitted a fix: #1058

The root cause is that both call sites in bbr_get_target_cwnd and bbr_get_a_state_target passed bw and gain in the wrong order to bbr_get_raw_target_cwnd. This caused bw (uint64_t) to be truncated to uint32_t and used as the gain multiplier, while the small gain value was used as the bandwidth, resulting in a severely underestimated congestion window.

This is an upstream FreeBSD bug (present in all FreeBSD versions including releng/13.0 through releng/15.0 and main). We are fixing it in F-Stack first. Thank you for the detailed report!