On Tue, 20 Feb 2024 09:50:13 -0500 Mathieu Desnoyers <mathieu.desnoy...@efficios.com> wrote:
> On 2024-02-20 09:19, Steven Rostedt wrote: > > On Mon, 19 Feb 2024 18:20:32 -0500 > > Steven Rostedt <rost...@goodmis.org> wrote: > > > >> Instead of using local_add_return() to reserve the ring buffer data, > >> Mathieu Desnoyers suggested using local_cmpxchg(). This would simplify the > >> reservation with the time keeping code. > >> > >> Although, it does not get rid of the double time stamps (before_stamp and > >> write_stamp), using cmpxchg() does get rid of the more complex case when > >> an interrupting event occurs between getting the timestamps and reserving > >> the data, as when that happens, it just tries again instead of dealing > >> with it. > >> > >> Before we had: > >> > >> w = local_read(&tail_page->write); > >> /* get time stamps */ > >> write = local_add_return(length, &tail_page->write); > >> if (write - length == w) { > >> /* do simple case */ > >> } else { > >> /* do complex case */ > >> } > >> > >> By switching the local_add_return() to a local_try_cmpxchg() it can now be: > >> > >> w = local_read(&tail_page->write); > >> again: > >> /* get time stamps */ > >> if (!local_try_cmpxchg(&tail_page->write, &w, w + length)) > >> goto again; > >> > >> /* do simple case */ > > > > Something about this logic is causing __rb_next_reserve() to sometimes > > always return -EAGAIN and triggering the: > > > > RB_WARN_ON(cpu_buffer, ++nr_loops > 1000) > > > > Which disables the ring buffer. > > > > I'm not sure what it is, but until I do, I'm removing the patch from my > > queue. > > Try resetting the info->add_timestamp flags to add_ts_default on goto again > within __rb_reserve_next(). > I was looking at that too, but I don't know how it will make a difference. Note, the test that fails is in my test suite, and takes about a half hour to get there. Running that suite takes up resources (it's my main test suite for all changes). I'm currently testing other patches so I either need to figure it out through inspection, or this will need to wait a while. -- Steve