I have an application that runs significantly slower in VTune than when run from a Linux shell. There are two primary threads in the application. When invoking from the shell, the main thread takes 100% of CPU time and the secondary thread takes about 15% consistently through the session. Overall time is about seven minutes.
When run in VTune, the secondary thread increases in time consumed during the overall session. It becomes the gating item in the session such that it is taking 100% of CPU time and the main thread is waiting for it and limited to 50% or lower utilization. The large item in the secondary thread reported is a call to fseek() on a large binary file. The secondary thread is writing the file and makes fseek() calls to do some annotation to previously written parts of the file.
When run in VTune, this application takes about 10 1/2 minutes, significantly longer than the seven minutes when run from the shell.
I'm using RHEL 7.6 on a linux_x86_64 system. I'm building my application using gcc 5.4.
What could account for the difference in behavior that I'm seeing? Is there anything that I can do to remedy the situation?
Thanks.
