Re: [Qemu-devel] [PATCH for-2.10 0/2] trace: fix simpletrace.stp flight recorder mode

[Stefan Hajnoczi]

On Mon, Aug 14, 2017 at 05:39:08PM +0100, Daniel P. Berrange wrote:
> On Mon, Aug 14, 2017 at 05:21:40PM +0100, Stefan Hajnoczi wrote:
> > The SystemTap flight recorder mode no longer works with simpletrace.stp 
> > because
> > the event ID mapping records are emitted the first time an event fires.
> > Chances are, the event ID mapping record will not be in ring buffer when the
> > users wants to print the trace.
> > 
> > This series solves the issue by using the trace-events-all global event
> > ordering for event IDs for simpletrace.stp.
> 
> I see the way you've written it means it'll still honour the event
> id mappings in the header, if present, but I wonder what's the point
> of keeping that anymore ? If we need to support this ring-buffer mode,
> there's no way we can take advantage of having the ID mappings dynamically
> defined - we must always guarantee a stable mapping.
> 
> IOW, should we just revert
> 
>   commit 7f1b588f20d027730676e627713ae3bbf6baab04
>   Author: Daniel P. Berrange <address@hidden>
>   Date:   Tue Oct 4 14:35:50 2016 +0100
> 
>     trace: emit name <-> ID mapping in simpletrace header
>     
> entirely ?

Follow-up to my reply:

We can revert just the changes to simpletrace_stap.py.  This means:

1. Event ID mapping records are no longer emitted.
2. No simpletrace file header is emitted.

I like this idea because it's simpler than my current patch.  Users will
have to use the ./simpletrace.py --no-header option again when printing
simpletrace.stp traces, but that isn't a problem.

Stefan

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