[parsec-users] what do 'user', 'real' time refer to

kishore kumar kishoreguptaos at gmail.com
Mon Dec 26 20:04:39 EST 2011


>>
'real' is the time spent in the parallelized phase of the benchmark(region
of interest)
>>
No. It is the turn-around time of the program. (Wall clock time)

>>
'user' is the time spent in the initialization and shutdown sequence.
>>
No. It is the time spent in user-space.

>>
'sys' probably refers to the operating system overhead.
>>
This is the time OS spends on behalf of the program (in kernel space).

For single threaded program,
real ~ (user + sys)

For multithreaded program, mostly you can expect that
user > real


Vijay,
I strongly recommend to refer the book "Advanced Programming in the UNIX
Environment" by Richard Stevens.


Best,
Kishore Kumar Pusukuri
http://www.cs.ucr.edu/~kishore



On Mon, Dec 26, 2011 at 4:26 PM, Vijay Thiruvengadam
<vijayaragha2 at wisc.edu>wrote:

> Hello
>
> I am a first year grad student. I am running the PARSEC benchmark
> Fluidanimate on a Intel QuadCore computer and am trying to make sense of
> the result obtained.
>
> I notice that I get the 'real', 'user' and 'sys' time as the outputs on
> running the benchmark with X number of threads. I keep changing the number
> of threads and observe the result. This question might seem too basic but I
> am not exactly sure what the 'real', 'user' and 'sys' terms refer to.
>
> As far as  understand, 'real' is the time spent in the parallelized phase
> of the benchmark(region of interest) and 'user' is the time spent in the
> initialization and shutdown sequence. 'sys' probably refers to the
> operating system overhead. Did I get this right?
>
> Also, I observe that the 'user' time always increases with increase in
> number of threads. Why is that?
>
> Thanks
> Vijay
> _______________________________________________
> parsec-users mailing list
> parsec-users at lists.cs.princeton.edu
> https://lists.cs.princeton.edu/mailman/listinfo/parsec-users
>
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