Description of problem:

The Global Thread Pool provides lower contention and increased performance in some cases, but it has been observed that sometimes there's a huge increment in the number of requests going to the disks in parallel which seems to be causing a performance degradation.

Actually, it seems that sending the same amount of requests but from fewer threads is giving higher performance.

The current implementation already does some dynamic adjustment of the number of active threads based on the current number of requests, but it doesn't consider the load on the back-end file systems. This means that as long as more requests come, the number of threads is scaled accordingly, which could have a negative impact if the back-end is already saturated.

The way to control that in current version is to manually adjust the maximum number of threads that can be used, which effectively limits the load on back-end file systems even if more requests are coming, but this is only useful for volumes whose workload is homogeneous and constant.

To make it more versatile, the maximum number of threads need to be automatically self-adjusted to adapt dynamically to the current load so that it can be useful in a general case.

Version-Release number of selected component (if applicable): mainline


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