a pet peeve of mine, (along with people brigading on issues/threads e.g. posting them to unrelated news sites... op....) is woefully incorrect language.

> at day 66 all our jobs started randomly failing

if there's a definable pattern, you can call it unpredictabily, but you can't call it randomly.

Crazy, so if I understand correctly, something with B200s and nvlink is causing issues where after 66 days and 12 hours of uptime, nvidia-smi and other jobs start failing, timing out, then once you restart the cluster it starts working again.

They suspect jobs will work if you only use 1 B200, but one person power cycled so wasn’t able to test it. Hopefully they won’t have to wait another 66 days for further troubleshooting.

*China specific code leaked into mainline.

66 days 14 hours and 24 minutes (66.6 days) would have been a far more diabolical hang...

NVLink postRxDetLinkMask errors show up right before the hang. Has anyone captured a bug report or stack trace while nvidia-smi is stuck to see what it's blocking on?

I wonder if the process to debugging this is just to search for what power of 2 times a time unit equals ~66 days

I think it's an overflow of a scaled counter.

Also, who else immediately noticed the AI-generated comment?

This is only very tangentially related, but I got flashbacks to a time where we had dozens of edge/IoT raspberry pi devices with completely unupgradeable kernels with a bug that would make the whole USB stack shut down after "roughly a week" (7-9 days) of uptime. Once it got shut down, the only way to fix it was to do a full restart, and, at the time, we couldn't really be restarting those devices (not even at night).

This means that every single device would seemingly randomly completely break: touchscreen, keyboard, modems, you name it. Everything broke. And since the modem was part of it, we would lose access to the device — very hard to solve because maintenance teams were sometimes hours (& flights!) away.

It seemed to happen at random, and it was very hard to trace it down because we were also gearing up for an absolutely massive (hundreds of devices, and then a couple of months later, thousands) launch, and had pretty much every conceivable issue thrown at us, from faulty USB hubs, broken modems (which would also kill the USB hub if they pulled too much power), and I'm sure I've forgotten a bunch of other issues.

Plus, since the problem took a week to manifest, we couldn't really iterate on fixes quickly - after deploying a "potential fix", we'd have to wait a whole week to actually see if it worked. I can vividly remember the joy I had when I managed to get the issue to consistently happen only in the span of 2 hours instead of a week. I had no idea _why_, but at least I could now get serviceable feedback loops.

Eventually, after trying to mess with every variable we could, and isolating this specific issue from the other ones, we somehow figured out that the issue was indeed a bug in the kernel, or at least in one of its drivers: https://github.com/raspberrypi/linux/issues/5088 . We had many serial ports and a pattern of opening and closing them which triggered the issue. Upgrading the kernel was impossible due to a specific vendor lock-in, and we had to fix live devices and ship hundreds of them in less than a month.

In the end, we managed to build several layers on top of this unpatchable ever-growing USB-incapacitating bug: (i) we changed our serial port access patterns to significantly reduce the frequency of crashes; (ii) we adjusted boot parameters to make it much harder to trigger (aka "throw more memory at the memory leak"); (iii) we built a system that proactively detected the issue and triggered a USB reset in a very controlled fashion (this effectively killed the network of the device for a while, but we had no choice!); (iv) if, for some reason, all else failed, a watchdog would still reboot the system (but we really _really_ _reaaaally_ didn't want this to happen).

In a way, even though these issues suck, it's when we are faced with them that we really grow. We need to grab our whole troubleshooting arsenal, do things that would otherwise feel "wrong" or "inelegant", and push through the issues. Just thinking back to that period, I'm engulfed by a mix of gratitude for how much I learned, and an uneasy sense of dread (what if next time I won't be able to figure it out)?

Timestamps should NOT be compared like this. Exactly this is why time_before() or time_after() exist.

https://elixir.bootlin.com/linux/v6.15.7/source/include/linu...