Re: script from chris mason

[Mike Mason <mmlnx at us dot ibm dot com>]

I forgot to mention that one way to capture more of the backtrace is to increase the maximum string size on the command line.

For example:

stap -DMAXSTRINGLEN=1024 io_submit.stp

This gives you 1024 bytes per array element to store backtraces instead of the default 128 bytes.

Mike

Mike Mason wrote:
> Hi Wenji,
>
> Thanks for sending this to the mailing list.  This is exactly what we 
> want to encourage. 
> I reviewed the script and made several changes:
>
> - Uses system call tapset for io_submit probes.
> - Uses tid() instead of pid().  That's the correct way to associate 
> events within a thread.
> - Removed separate variables for array indexes. They're unnecessary in 
> this case.
> - Uses the array membership check feature in the schedule probe.
> - Uses the '-' operator on the traces array in the end probe.  
> Eliminates the need to presort the array.
>
> I confirmed that the script with my changes would build and run, but was 
> unable to trigger the conditions that cause backtraces to be collected.  
> Can you or Chris test this in your environment?
>
> Once the script is finalized, it would be great to document it in the 
> War Stories section of the wiki.  We could also include it in Scripts & 
> Tool on the wiki and the examples directory in cvs if we think it is of 
> general interest.
>
> Thanks,
> Mike
>
>
> Wenji Huang wrote:
> > Hi,
> >
> > This is the script from Chris Mason <chris.mason@oracle.com>. It could 
> > find the most common causes of schedule during the AIO io_submit call. 
> > I think it's very good that a kernel developer can use systemtap and 
> > share his script.
> >
> > Please review it and where it is putted?   how about in examples?
> >
> > Thanks,
> > Wenji