On Tue, Oct 7, 2025 at 2:43 PM Doug Anderson <[email protected]> wrote: ... > The buddy watchdog was pretty much following the conventions that were > already in the code: that the hardlockup detector (whether backed by > perf or not) was essentially called the "nmi watchdog". There were a > number of people that were involved in reviews and I don't believe > suggesting creating a whole different mechanism for enabling / > disabling the buddy watchdog was never suggested.
I suspect they lacked the context that 1 in the nmi_watchdog is taken to mean there's a perf event in use by the kernel with implications on how group events behave. This behavior has been user visible/advertised for 9 years. I don't doubt that there were good intentions by PowerPC's watchdog and in the buddy watchdog patches in using the file, that use will lead to spurious warnings and behaviors by perf. My points remain: 1) using multiple files regresses perf's performance; 2) the file name by its meaning is wrong; 3) old perf tools on new kernels won't behave as expected wrt warnings and metrics because the meaning of the file has changed. Using a separate file for each watchdog resolves this. It seems that there wasn't enough critical mass for getting this right to have mattered before, but that doesn't mean we shouldn't get it right now. Thanks, Ian
