Hello Anthony,
Monday, January 3, 2005, 2:00:25 AM, you wrote:
AJC> Hello All,
AJC> I have noticed that the elapsed time is not equal to the sum of the user
AJC> and system times when using the tcp modules. For example, one might
AJC> record;
AJC> user time: 550s
AJC> sys time : 50s
AJC> real time: 750s
AJC> I first suspected that the missing time was the time in which the
AJC> communication actually happened; however, the opposite of that seems to be
AJC> happening.
AJC> In a job which transferes a total of:
AJC> 4 gigabytes 1 gigabyte
AJC> user 580 650
AJC> sys 60 30
AJC> real 760 850
AJC> -----------------------------------
AJC> diff 120 170
AJC> The times are close, even though one program transfered one-fourth of the
AJC> data of the other. There may have been a difference in the size of the
AJC> packets, but they should have all been large.
AJC> Does anyone know a fairly good network profiler for 2.6.x kernels to look
AJC> into whats happening? Or does anyone know about this missing time right
AJC> off?
AJC> And what ever happened to M-VIA and VIA? They would help reduce processor
AJC> load some. Is it just that TCP can pump stuff out at near wire-speed as
AJC> it is, so there is no need for VIA? Has anyone ever thought of using
AJC> IPX/SPX networks? For clusters, they might be more efficient than TCP/IP.
AJC> ------------------------------------------------------------
AJC> Anthony Ciani (aciani1_at_[hidden])
AJC> Computational Condensed Matter Physics
AJC> Department of Physics, University of Illinois, Chicago
AJC> http://ciani.phy.uic.edu/~tony
AJC> ------------------------------------------------------------
AJC> _______________________________________________
AJC> This list is archived at http://www.lam-mpi.org/MailArchives/lam/
Answer to Your question about times is simlpe: the "real" time isn't
just a sum of "user" time and "system" time. Real time is time that
passed from when Your process started, so it is a sum of system and
user times of *all* processes in Your system plus time for OS specific
functions like memory paging etc. , counted since Your LAM
process (process that calls times()) started.
--
Best regards,
Simon
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