[petsc-dev] MatMult on Summit

[Smith, Barry F.]

  Ok, thanks. Then one has to be careful in HPC when using the term so each time it is used everyone in the conversation knows which one it is referring to. 


> On Sep 22, 2019, at 8:33 AM, Jed Brown <jed at jedbrown.org> wrote:
> 
> "Smith, Barry F." <bsmith at mcs.anl.gov> writes:
> 
>>> On Sep 21, 2019, at 11:43 PM, Jed Brown <jed at jedbrown.org> wrote:
>>> 
>>> "Smith, Barry F." <bsmith at mcs.anl.gov> writes:
>>> 
>>>> Jed,
>>>> 
>>>> What does latency as a function of message size mean?   It is in the plots
>>> 
>>> It's just the wall-clock time to ping-pong a message of that size.  All
>>> the small sizes take the same amount of time (i.e., the latency), then
>>> transition to being network bandwidth limited for large sizes.
>> 
>>   Thanks, this is fine for the small size. But he has the graph up to
>>   size 1000000 and the plotted values change for larger sizes, surely
>>   for 1000000 the time is a combination of latency and bandwidth?
>>   Isn't calling it latency a misnomer, or do people use this
>>   inconsistent terminology when doing ping-pongs?
> 
> Latency of an operation is just how long from when you initiate it until
> it completes.  Latency in a performance model, such as LogP, is additive
> with other factors (like bandwidth and compute throughput).