Hi Peter and Ingo, On Tue, Nov 26, 2024 at 05:13:45PM -0500, Vince Weaver wrote: > On Sat, 23 Nov 2024, Mikołaj Kołek wrote: > > > findings. In the MMAP layout section of the page, you can find this > > sentence: > > Before Linux 2.6.39, there is a bug that means you must allocate > > an mmap ring buffer when sampling even if you do not plan to > > access it. > > Unless I'm somehow misunderstanding it, this statement does not seem > > to be well worded, or alternatively this bug does not seem to be > > fixed. > > That text was probably written by me. > > I tried looking at the 2.6.39 code, my perf_tests, and also PAPI which was > where the problem was probably noticed but I can't find a firm reference > for how the issue was fixed. > > If I recall, the problem was if you were trying to create a sampling event > without mmap (say you want to get a signal every 100,000 retired > instructions, but you don't actually want any sample data). I think > before 2.6.39 if you tried setting that up you'd get some sort of error > (an EINVAL?) when trying to start(?) the event. > > It is possible this wasn't fixed. I tried to be pretty good > about putting relevant git commits as comments in the manpage but there > doesn't seem to be one for that part of the text. I'm guessing it was > PeterZ doing the work on this so maybe he remembers. Do you remember what was the issue exactly on sampling events w/o mmap? Thanks, Namhyung
