Hi,
I was working on the Linux CFS scheduler and came across this tuneable parameter called `sched_wakeup_granularity_ns`. The use of this goes as follows as described in [this paper](http://rouskas.csc.ncsu.edu/Publications/Conferences/ICC-SPS-2015.pdf ).
> This parameter controls the wake-up latency of a task, i.e., the amount of time it must lapse before it can preempt the current task.
Further looking up on this parameter from [here](https://www.systutorials.com/239998/sched_min_granularity_ns-sched_latency_ns-cfs-affect-timeslice-processes/ ) :
> If the difference between the virtual run time of current running process and the virtual run time of preempting process is bigger than the virtual run time of sched_wakeup_granularity_ns (here, transfer sched_wakeup_granularity_ns to a virtual run time with preempting process’s weight), the preemption happens.
The default value of this in my system is 2.5 milli seconds.
My question : If a process with a deadline <= 2.5 ms comes at time another low priority process is executing then, it won't get its chance to execute because of this minimum granularity and will always miss its deadline.
Am I right in my claim ? Why is the Linux kernel designed like that ?
Of course we can set this parameter to 0 ms and re-compile the kernel, but don't tasks with deadlines of 2.5 ms occur frequently in day to day life ? Video decoders, sound processing apps, and other latency critical workloads ?
I was working on the Linux CFS scheduler and came across this tuneable parameter called `sched_wakeup_granularity_ns`. The use of this goes as follows as described in [this paper](http://rouskas.csc.
> This parameter controls the wake-up latency of a task, i.e., the amount of time it must lapse before it can preempt the current task.
Further looking up on this parameter from [here](https://www.
> If the difference between the virtual run time of current running process and the virtual run time of preempting process is bigger than the virtual run time of sched_wakeup_granularity_ns (here, transfer sched_wakeup_granularity_ns to a virtual run time with preempting process’s weight), the preemption happens.
The default value of this in my system is 2.5 milli seconds.
My question : If a process with a deadline <= 2.5 ms comes at time another low priority process is executing then, it won't get its chance to execute because of this minimum granularity and will always miss its deadline.
Am I right in my claim ? Why is the Linux kernel designed like that ?
Of course we can set this parameter to 0 ms and re-compile the kernel, but don't tasks with deadlines of 2.5 ms occur frequently in day to day life ? Video decoders, sound processing apps, and other latency critical workloads ?
- RR
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