Linux Doc

CFS Scheduler

Code Go Through

RT linux source Code - sched_class identifier

Fixing SCHED_IDLE

Elements in the Task Structure

sched_class Struct Reference 3.7.1

Understanding sched_class

Policy define:

#define SCHED_NORMAL 0
#define SCHED_FIFO 1
#define SCHED_RR 2
#define SCHED_BATCH 3
#define SCHED_IDLE 5

Processes under SCHED_NORMAL, SCHED_BATCH and SCHED_IDLE are mapped to fair_sched_class, provided by CFS. SCHED_RR and SCHED_FIFO associate with rt_sched_class, real-time scheduler. (A complete guide to Linux process scheduling)

awk '/policy/ {print $NF}' /proc/*/sched |sort | uniq

PID=2911
awk '/policy/ {print $NF}' /proc/$PID/sched

chrt -ap $PID

what is the use of .next field in sched_class structure?

Linux Scheduler

How to find scheduling policy and active processes' priority?

TS is SCHED_OTHER
RR is SCHED_RR
FF is SCHED_FIFO

ps -e -o s,pid,cls,pri | grep ^R | awk -v sq="'" '{print "pid",$2,sq,"s current scheduling policy:",$3,"\npid",$2,sq,"s current priority:",$4}'

ps -e -o s,pid | grep ^R | awk '{system("chrt -p " $2)}'

ls /proc | grep -e ^[0-9] | awk '{system("chrt -p " $0)}'|more

How to change scheduling algorithm and priority used by a process?

PID=7861 

tuna --threads $PID --priority=RR:40    # <<-- sets a policy of RR (round-robin) and a priority of 40 for PID 7861.

How to check the process scheduling policy other than `ps` output

PID=25
awk '/policy/ {print $NF}' /proc/$PID/sched

Linux Kernel Development

It will be added a new scheduling policy to the CISTER framework. The scheduling algorithm is the well known Last-In First-Out (LIFO). According to LIFO scheduling algorithm, the last task ready for execution execution will be selected to be executed. That is, whenever a task arrives (become ready for execution) the currently executing is preempted and the recently arrived task is selected for execution.

A set of steps is required to add a new scheduling policy. REF: http://www.cister.isep.ipp.pt/summer2017/w1/S3_Lab.pdf

Note that, almost all functions have as arguments pointers of struct task_struct and struct rq. The lf_sched_class scheduling policy it is positioned between the RT and CFS scheduling classes.