Hi, On Tue, Oct 7, 2025 at 3:45 PM Ian Rogers <[email protected]> wrote: > > 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.
Presumably your next steps then are to find someone to submit a patch and try to convince others on the list that this is a good idea. The issue with perf has been known for a while now and I haven't seen any patches. As I've said, I won't stand in the way if everyone else agrees, but given that I'm still not convinced I'm not going to author any patches for this myself. -Doug
