[Darshan-users] Does Darshan uses CPU time ?

[Harms, Kevin]

Florian,

  STDIO_F_META_TIME should be the time spent in metadata accumulated across the processes if it is shared. The rank for the file would be -1 if it is shared.

  So for example:
    4 processes run for 10 seconds
    each process opens foo.txt for 1 second
    1 process stats foo.txt for 1 second

    the results would be foo.txt shows 5 seconds of meta time for foo.txt. So you can do 5 seconds / 4 processes for an average of 1.25s or you could do 5s / (10s * 4p) = 0.125 or 12.5%.

  If the rank value is > -1, the the reported time is just for that one rank and you need to potentially sum them up.

  If you meta time for a single file exceeds the runtime * number of processes, then something must be wrong with the timer collection. Can you send the log file? You can also look at the _START_TIMESTAMP and _END_TIMESTAMP and see if those agree with runtime or not?

kevin



________________________________________
From: Darshan-users <darshan-users-bounces at lists.mcs.anl.gov> on behalf of Florian Lecomte <flo.lecomte17 at gmail.com>
Sent: Tuesday, August 3, 2021 9:37 AM
To: darshan-users at lists.mcs.anl.gov
Subject: [Darshan-users] Does Darshan uses CPU time ?

Good evening,
I'd like to know if I have to divide metrics by the number of CPUs of the machine I use if I want to know the percentage of time spent on write operations for example.
Because when I divide for example STDIO_F_META_TIME by [real runtime (time spent in "real world") * number of processes], I often get something bigger than 1, which is not supposed to happen.
So to sum it up : Does Darshan give the average metric value per process per CPU, or only per process, and so it can not be compared with real spent time ?

Thank you very much.
Cordially, Florian, student in the HPC field.