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

Vijay Thiruvengadam vijayaragha2 at wisc.edu
Mon Dec 26 20:10:12 EST 2011


Thanks a lot for your reply.

On Dec 26, 2011, at 7:04 PM, kishore kumar wrote:

> >>
> '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
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