CODEWITHSUNDEEP
linuxlinux-kernelembedded-linux
dexterous
dexterous

Reputation: 6526

How to identify the scheduling algorithm and pre-emptive/non-preemptive nature of the Linux machine?

I know that by default Linux is pre-emptive. I want to know on the running Linux machine about the scheduling algorithm that has been devised. Also, I want to know whether it is pre-emptive or not?

While we configure our kernel, we have an option on scheduling - Round Robin, etc. But, how to identify on Run-time the scheduling policy of the linux system. Also, whether it is preemptive or not.

Upvotes: 2

Views: 857

Answers (2)

kaiwan
kaiwan

Reputation: 2144

Firstly, are you referring to the Linux IO or process scheduler? If the IO scheduler, then some answers have been provided..

Process scheduler-wise, the Linux kernel can be configured with different options while doing 'make menuconfig'. As an example, for an ARM system:

cd <kernel-src-tree>
make ARCH=arm menuconfig
...
Under Kernel Features:

       Preemption Model (Preemptible Kernel (Low-Latency Desktop))  ---> 
              ( ) No Forced Preemption (Server)
              ( ) Voluntary Kernel Preemption (Desktop)
              (X) Preemptible Kernel (Low-Latency Desktop)

If you apply the (hard) RT patch, you will get a fourth option: CONFIG_PREEMPT_RT (implying you're essentially running Linux as an RTOS).

Also, you can check your current config by looking up the kernel config file. Eg. on a desktop Ubuntu 13.10 running the 3.11.0-15-generic kernel:

# grep -i preempt /boot/config-3.11.0-15-generic 
# CONFIG_PREEMPT_RCU is not set
CONFIG_PREEMPT_NOTIFIERS=y
# CONFIG_PREEMPT_NONE is not set
CONFIG_PREEMPT_VOLUNTARY=y
# CONFIG_PREEMPT is not set
# 

# grep -i SCHED /boot/config-3.11.0-15-generic 
CONFIG_HAVE_UNSTABLE_SCHED_CLOCK=y
CONFIG_CGROUP_SCHED=y
CONFIG_FAIR_GROUP_SCHED=y
CONFIG_RT_GROUP_SCHED=y
CONFIG_SCHED_AUTOGROUP=y
# IO Schedulers
CONFIG_IOSCHED_NOOP=y
CONFIG_IOSCHED_DEADLINE=y
CONFIG_IOSCHED_CFQ=y
CONFIG_CFQ_GROUP_IOSCHED=y
CONFIG_DEFAULT_IOSCHED="deadline"
...

Notice the IO sched values too are shown.

Upvotes: 2

Tharanga Abeyseela
Tharanga Abeyseela

Reputation: 3483

Try the following.This give you the scheduler your Linux system is using .

more /sys/block/sdX/queue/scheduler (sdX = sda or sdb , depend on your system)

Othe method is to use

make menuconfig

this will list you all scheduling algorithms and the one you are using.

Upvotes: 2

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