Hello-

I am trying to understand how to properly use TOP & SAR. I am on Oracle Linux 7, there is a process that is running into issues and in TOP shows 100% for CPU, however SAR does not show CPU at 100 but somewhere in 20,15 % range. This server has hyper threading and is a 16 processer( from cat /proc/cpuinfo).

Does Linux by default allocate CPU per process ? So of 16 CPU only 1 is at 100% ? IS there any settings I should look into ? I am not trying to increase CPU for that process but want to understand why top & sar show different values.

A single process can, by definition, only occupy a single CPU (core/physical thread/whatever) at any instant in time. It doesn't always have to be the same CPU although for performance reasons (cache, TLB flushing) it often is. This applies to every operating system ever invented.Because you're comparing apples to oranges.
In top the values for individual processes are un-normalised - simply the total CPU usage for the latest time period. For a non-threaded process this will never exceed 100% except for rounding errors. For a (busy) multi-threaded task, it may exceed 200 or 300%.
Depending on the options passed to sar you are likely looking at the total CPU usage for the entire system - and as mentioned your busy task may not reside on one CPU exclusively. You can also see the individual CPU usage in the summary data of top.

I would rather say a single threaded process can only use a single core. But multithreaded processes may use more cores at any time.