I have written an application (Qt/C++) that creates a lot of concurrent worker threads to accomplish its task, utilizing QThreadPool (from the Qt framework). It has worked flawlessly running on a dedicated server/hardware.
A copy of this application is now running in a virtual machine (RHEL 7), and performance has suffered significantly in that the queue (from the thread pool) is being exercised quite extensively. This has resulted in things getting backed up a bit. This, despite having more cores available to the application through this VM version than the dedicated, non-virtualized server.
Today, I did some troubleshooting with the top -H -p <pid> command, and found that there were 16 total llvmpipe-# threads running all at once, apparently for software rendering of my application's very simple graphical display. It looks to me like the presence of so many of these rendering threads has left limited resources available for my actual application's threads to be concurrently running. Meaning, my worker threads are yielding/taking a back seat to these.
As this is a small/simple GUI running on a server, I don't care to dedicate so many threads to software rendering of its display. I read some Mesa3D documentation about utilizing the LP_NUM_THREADS environment variable, to limit its use. I set it to LP_NUM_THREADS=4, and as a result I seem to have effectively opened up 12 cores for my application to now use for its worker threads.
Does this sound reasonable, or will I pay some sort of other consequence for doing this?