VTune skew on application with lots of file i/o

[ChuckP]

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.

[JaideepK_Intel]

Hi,

Thank you for posting in Intel communities.

Could you please share the below details?

1. We can see you are using RHEL7, which is not currently supported (deprecated) by the latest version of Vtune, so please try the same on a supported operating system.

link: https://www.intel.com/content/www/us/en/developer/articles/system-requirements/vtune-profiler-system-requirements.html

1. If you face the same issue on a supported OS, please share the processor details and exact steps to reproduce your issue, Please share a sample reproducer (exact replica of your sample) so we can debug further.

Thanks,

Jaideep

[JaideepK_Intel]

Hi,

Could you please try Intel Vtune on the supported operating system and let us know if you still face any issues?

Thanks,

Jaideep

[ChuckP]

Hi--

I spent some time writing a demonstration program, but was unable to reproduce the anomalous behavior with that.  Then I rebuilt and re-ran my real application.  Upon re-trying, I found it worked OK in VTune.

I'm mystified as to what was going on.  Thank you for your concern, but I don't have an issue that needs investigation right now.

Thanks.

[JaideepK_Intel]

Hi,

It's good to hear that your rebuild samples are working on Vtune. If you need any additional information, please post a new question as this thread will no longer be monitored by Intel.

Thanks,

Jaideep