Messages in this thread | | | Date | Wed, 7 Nov 2018 20:43:44 +0100 | From | Jiri Olsa <> | Subject | Re: [PATCH RFC] hist lookups |
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On Wed, Nov 07, 2018 at 09:32:17AM +0100, Jiri Olsa wrote: > On Tue, Nov 06, 2018 at 10:13:49PM -0800, David Miller wrote: > > From: Jiri Olsa <jolsa@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
I pushed new version in my perf/fixes branch
jirka
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