On Tue, Nov 06, 2018 at 10:13:49PM -0800, David Miller wrote: > From: Jiri Olsa <jo...@redhat.com> > Date: Tue, 6 Nov 2018 21:42:55 +0100 > > > I pushed that fix in perf/fixes branch, but I'm still occasionaly > > hitting the namespace crash.. working on it ;-) > > Jiri, how can this new scheme work without setting copy_on_queue > for the queued_events we use here?
aahh.. it won't, setting it up ;-) > > I don't see copy_on_queue being set and that means the queued event > structures reference the event memory directly in the mmaps, after the > mmap thread has released them back to the queue. > > That means new events can come in to the mmap ring and overwrite what > was there previously, maybe even while deliver_event() is in the > middle of parsing the event. > > Setting copy_on_queue for data[0] and data[1] makes all of the crashes > go away for me. > > I get a lot of "[unknown]" shared objects shortly after perf top > starts up during a full workload. I've been wondering about one > side effect of how the mmap queues are processed, consider the > following: > > cpu 0 cpu 1 > > exec > create new mmap2 events > scheduled to cpu 0 for whatever reason > sample 1 > sample 2 > > And let's say that perf top is backlogged processing the mmap ring of > events generated for cpu 0, and sees sample 1 and sample 2 before > getting to any of cpu 1's events. > > This means the thread and map and symbol objects won't exist and > we'll get those '[Unknown]' histogram entries, and they won't go > away. > > When it finally stops looping over the mmap ring for cpu 0's events > it gets to cpu 1's mmap ring and sees the exec and mmap2 events > but at that point it's far too late. > > I surmise from what I see with perf top right now that this happens > a lot. right, there's no reason why top should have different standards than record/report.. above can definitely happen, I'll enable time sample type and use ordered events for the queue jirka
