topic Re: Real Time vs CPU time in SAS Programming

Real Time vs CPU time

Cobrad — Thu, 28 Jul 2016 09:22:52 GMT

Dear SAS

What is the difference between Real Time and CPU Time?

What makes the one faster than the other? I have noticed in my log that sometimes when a data step runs quickly the CPU Time can be longer than the Real Time, but on the long/large run times the Real Time is always very much longer than the CPU Time.

Thanks for you help!!

Re: Real Time vs CPU time

rivieralad — Thu, 28 Jul 2016 12:42:34 GMT

Quick/simple answer, but I am sure someone will provide a far more technical response.

Real Time is the actual, real world, time that the step takes to run and will be the same as if you timed it with a stopwatch (not possible as you won't know the precise moment the step starts and stops).

CPU Time is the amount of time the step utilises CPU resources. If the machine on which the step is running has only a single CPU then the total CPU time would always be less than than the real time.

However, with multiple processor machines, the load is spread across multiple CPU's and the total CPU time (as reported on the log) may be longer than the real time, e.g. a data step may take 2.6 seconds of real time to execute but the load is spread across 4 CPUs, utilising 1 second of resource on each, so the CPU time will be 4 seconds, i.e. 1.4 seconds longer than the real time.

The nature of the step will heavily influence the real and CPU times, processing data will utilise the CPU but data i/o will increase real time as the data is read from and written back to disk.

There is a lot of information about performance techniques, utilising in-memory processing, etc., available on the web.

Hope this helps.

Cheers

Chris

Re: Real Time vs CPU time

Cobrad — Thu, 28 Jul 2016 13:21:52 GMT

Thanks Chris

This really helps a lot!!

Have a great day.

C.

Re: Real Time vs CPU time

ballardw — Thu, 28 Jul 2016 16:24:19 GMT

You might be interested in setting the system option FULLSTIMER for some jobs to show more performance related information. The default setting is usually NOFULLSTIMER .

If interested add:

options FULLSTIMER;

before the data step or procedures you are interested in.

Re: Real Time vs CPU time

Cobrad — Sat, 30 Jul 2016 15:00:41 GMT

Awesome - thanks a lot for the info.

Much appreciated.

C.

Re: Real Time vs CPU time

sgarg-tester — Tue, 20 Feb 2018 00:30:32 GMT

Hello Chris,

Thanks for the reply. I have a question (or confusion) w.r.t. real time definition here. In my view, SAS has its Real World defined in terms of Code, CPUs, Memory, Network, Hardware etc. which in turn may be interacting with system say an Oracle database which has similar Real World. So, please correct me If I am wrong. I interpreted your answer as...

Real World is - When a user's program gets executed on SAS system and assume it is creating and printing a SAS DataSet by fetching some data from an Oracle database, then real world time means the total turn around time for the entire operation including Compile time, Syntax checking, Memory allocation, data set creation and so on until data is being printed and displayed to the user.

CPU Time is - For this entire set of activities, how much time is taken by CPU only? But isn't everything needs a CPU time?

Please guide.

Thanks

-Sandeep

Re: Real Time vs CPU time

ChrisNZ — Tue, 20 Feb 2018 01:41:35 GMT

>But isn't everything needs a CPU time?

No. Often, the CPU is waiting for the disk or the network, or even the RAM, and can't process anything. Idle CPU time is not CPU time.