如何确定任务是否在Linux内核中绑定了I / O？

Question

I am trying to implement scheduler for linux kernel ( version 2.4.27 ) and I am trying to find out whether a task is CPU bound or I/O bound. Are there any variables/function which I can use to get this information?

Answer 1

If talking about O(1) Scheduler:

A process can be determined as CPU bound or I/O bound based on the timeslice it runs on the CPU.

Every process will have its default timeslice(100ms) set before allowing it to be scheduled on a processor.

A process is called a CPU bound process, if the very process consumes full time slice(runs for the entire time slice on the processor).

Similarly, any process that doesn't consume its entire timeslice, but would call sched_yield even before its timeslice has run-out, or , if the process waits/sleeps for any event to occur, then the scheduler will be invoked to push it to sleeping queue, which means it is waiting for some I/O to happen, is an I/O bound process.

Every such CPU bound process will be penalized with priority, keeping the time slice same, and every such I/O bound process will be appreciated with a bonus of priority, keeping the time slice same.

So, on an GPOS(General Purpose Operating System), it is the effective_priority or dynamic_priority, that will tell you if the process is well-behaved(I/O bound) or ill-behaved(CPU bound process), as the default priority will be 20 for a new process, unless it is altered otherwise.

There are some parameters based on which, you can determine the same.

effective_prio: Returns the effective priority of a task (based on the static priority, but includes any rewards or penalties).

recalc_task_prio: Determines a task's bonus or penalty based on its idle time.

Ref: https://www.cs.columbia.edu/~smb/classes/s06-4118/l13.pdf