UNIX for Advanced & Expert Users

Let's suggest that we do physical read involving OS cache.
Also suggest that our cache is huge and CPU and disk are very slow that searhcing in cache consumes about 5 seconds and after that request data from disk is 10 seconds.

Code:

pread begin
  search_in_OS_cache(); << we are in searching from cache now
  
  if not_found_in_cache then
    request_from_disk();
  end if
pread end

What we will see in prstat for these thread for this 5 seconds during searching in OS cache? As I understand process state will be CPUn, right ? Will this thread be considered as blocked? As I understand now - not. Is it right?

After 5 seconds data is not found in the cache and we have to request it from disk.
So,

Code:

pread begin
  search_in_OS_cache(); 
  
  if not_found_in_cache then
    request_from_disk(); << we are here now
  end if
pread end

10 seconds we are waiting respons from disk.

What we will see in prstat for these thread for these 10 seconds? As I understand process state will be sleeping, right ? Will this thread be considered as blocked (I mean the thread a candidate for vmstat.b)? As I understand - yes. Is it right?

You'd be incorrect. System calls don't run inside the process. That's the difference between a system call and a function call... functions are just different code running inside the process, system calls are a message passed to the kernel. The process stops until the kernel starts it again.

Think of it this way. System calls are a process asking something else to do work for it. It doesn't do it itself, it hands it off to the kernel, passes a message. To pass this message, the process is automatically stopped. That's how system calls work.

It is interesting.
What if I have 50 processes on the host with 100 CPU cores. And let's suggest in some moment of time ALL of them are entering in some CPU expensive syscall. As an example syscall searching data in cache. So, in this moment of time all of them in syscall.
Which state will they have in prstat? I mean exactly column STATE in prstat

---------- Post updated at 11:50 PM ---------- Previous update was at 11:44 PM ----------

Yes, I am understanding your point of view. I just trying to understand which state a process has inside syscall and when it became blocked?

My understanding that
- when a process inside syscall on CPU his state in prstat is "CPUn".
- when a process inside syscall waiting response from a disk his state in prstat is "sleeping". And in the same time the process is considered as blocked. In this moment column vmstat.b will be increased.
Is it right?

So, about your point.
All consumed CPU should be recorded for some process(or thread). Let's suggest that we have IDLE system with only one running thread. This thread is entering into CPU consuming syscall. Syscall will consume about 100 hours of CPU.
Which state the thread will have in these 100 hours?
Will CPU time of the thread be increased on 100 hours?