Messages in this thread | | | Date | Wed, 18 Aug 2010 08:40:48 +1000 | From | Dave Chinner <> | Subject | Re: [tracing, hang] dumping events gets stuck in synchronise_sched |
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On Tue, Aug 17, 2010 at 09:02:38AM -0400, Steven Rostedt wrote: > On Tue, 2010-08-17 at 21:52 +1000, Dave Chinner wrote: > > On Tue, Aug 17, 2010 at 04:37:44PM +0800, Lai Jiangshan wrote: > > > On 08/17/2010 03:37 PM, Dave Chinner wrote: > > > > Tracing folks, > > > > > > > > I've got a machine stuck with a cpu spinning in a tight loop (the > > > > new writeback/sync livelock avoidance code is, well, livelocking), > > > > and I was trying to find out what triggered by using the writeback > > > > trace events. Unfortunately, I can't dump the trace events because > > > > it gets stuck here: > > > > > > > > > > > Given that the trace events are there mainly for debugging, this > > > > seems like a bit of an oversight - hanging a CPU in a tight loop is > > > > not an uncommon event during code development.... > > > > > > > > > > You can try 'cat trace_pipe', if I did not miss you meaning. > > > > I'll try it, but I'm really after the static event list which is why > > I'm using the trace file rather than trace_pipe. I want the history, > > not new events as they happen. > > When the systems locks up, I assume you want to see why? The trace_pipe > should show that without locking the system.
Exactly.
> You could also try downloading trace-cmd and running the tracer with > that. That will save all traces to a file while running the trace.
I don't have tens of GB available to store all the traces that an xfstests test run generates. In general, I don't need the traces, either, and when I do the problem is usually in the current ring buffer, which is why I typically dump the events after the fact.
If the trace file cannot be made to handle this type of use robustly, then perhaps it should be removed...
Cheers,
Dave. -- Dave Chinner david@fromorbit.com
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