RE: [PATCH 1/1] perf,tools: add time out to force stop endless mmap processing

[Liang, Kan]

> 
> > The maps information is not critical for sampling.
> 
> But is for correlating the addresses in those samples.

We still have the maps information for other threads in system.
Only part of the information for some thread is lost.

> 
> >
> > If task_diag does not solve this problem, I think we still need a time
> > out to force stop endless mmap processing. It's the simplest working
> > solution so far.
> 
> I disagree with the timeout. For example an overloaded system where
> perf is not getting scheduled could trigger the same.

It's not a perfect solution for all tools. But a working solution for perf.
Without timeout, we get nothing from perf top/record.
With timeout, we can do sampling. We can correlate the addresses in
most samples. It's better than nothing.

> 
> Also, in the spirit of perf if you are going to drop information you need to
> generate an event that says information was lost and have the analysis
> tools show a message that information was lost. You can't simply bail out
> and have "[unknown]" shown for symbols / dsos. I get tons of user
> comments about perf showing callchains properly; the proposed patch just
> adds to that confusion.

Currently, it will print a warning in perf top/record. I think I can do more and
print warning in perf_session__warn_about_errors as Arnaldo suggested.
 
Thanks,
Kan


> 
> David
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