[mpiwg-tools] reset a stopped pvar

[Kathryn Mohror]

Hi Junchao,

> 
> Also, for a stopped pvar, after reset and before restarting, what does a pvar_read return?
> Returning zero sounds good for counters? What about watermarks? Old value, garbage value or MPI_T_ERROR_XXX? I would choose ERROR.
> The side-effect is that it makes resetting pvars not beautiful.

In my interpretation, it returns the starting value of the variable as defined according to the variable class. So, for watermarks, it would be the current value at the time of the reset. I can imagine a scenario where you want to know what the starting value  of a variable is for some reason, so you wouldn't want it to be erroneous for a tool to read a non-started variable.

Do others agree with this?

Kathryn

> 
> --Junchao Zhang
> 
> On Thu, Sep 19, 2013 at 12:32 AM, Martin Schulz <schulzm at llnl.gov> wrote:
> Hmm, that is a good catch. I agree with Kathryn's interpretation - in particular the use case she is laying out. If one does:
> 
> Reset
> Start
> Stop
> 
> You want the watermark from that interval, i.e., the starting value as of the start call should be the right thing. This is something we definitely should clarify.
> 
> Thanks,
> 
> Martin
> 
> 
> 
> On Sep 18, 2013, at 8:33 PM, Kathryn Mohror <kathryn at llnl.gov>
>  wrote:
> 
>> Hi Junchao,
>> 
>>>   What is the right behavior when resetting a stopped pvar? The standard says setting to its starting value.
>>>   For counters, timers etc, setting them to zero sounds reasonable.
>>>   But for a watermark, setting it to "the current utilization level" looks weird. It implies that a value caught during the stopped period can affect its future value when the pvar is re-started.
>>>   Probably, we should reset a stopped watermark to a state as if it has never been started.
>>>   Any comments?  Thanks
>> 
>> Hmm. It makes sense to me, but I'll let others chime in if they disagree. I think that the moment you start the watermark variable, you want to know what the "mark" is, so it would be the value of current utilization. So even if a higher (or lower) value is caught during the stopped period (which it shouldn't be, because variables aren't supposed to be updated when stopped), it will be set to the current utilization value when started. I interpret this as being able to measure the watermark during different epochs of the program execution. Every time you start the variable, it's a fresh epoch and you want to know what the watermark was during that epoch.
>> 
>> However, I can see how this isn't clear as it could be -- I'll try to see what we can do to clarify it in the text.
>> 
>> Thanks again for taking the time to give us this feedback.
>> 
>> Kathryn
>> 
>> 
>>> --Junchao Zhang
>>> _______________________________________________
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>>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-tools
>> 
>> ______________________________________________________________
>> Kathryn Mohror, kathryn at llnl.gov, http://people.llnl.gov/mohror1
>> CASC @ Lawrence Livermore National Laboratory, Livermore, CA, USA
>> 
>> 
>> 
>> 
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>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-tools
> 
> ________________________________________________________________________
> Martin Schulz, schulzm at llnl.gov, http://people.llnl.gov/schulzm
> CASC @ Lawrence Livermore National Laboratory, Livermore, USA
> 
> 
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______________________________________________________________
Kathryn Mohror, kathryn at llnl.gov, http://people.llnl.gov/mohror1
CASC @ Lawrence Livermore National Laboratory, Livermore, CA, USA




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