[mpiwg-tools] reset a stopped pvar

[Junchao Zhang]

For a running (i.e., started) watermark, it is reasonable to return the
starting value.
But for a stopped one, it is strange to do a read and return what is read.

--Junchao Zhang


On Thu, Sep 19, 2013 at 11:03 AM, Kathryn Mohror <kathryn at llnl.gov> wrote:

> 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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>>
>>  ______________________________________________________________
>> Kathryn Mohror, kathryn at llnl.gov, http://people.llnl.gov/mohror1
>> CASC @ Lawrence Livermore National Laboratory, Livermore, CA, USA
>>
>>
>>
>>
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>>
>> ________________________________________________________________________
>> 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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