Re: sched: Clarify PREEMPT is full preemption model

[Shrikanth Hegde]

Please use plaintext for sending mail containing patches.
Not able to see the patch on my mail client.  Also the text is not formatted.

https://docs.kernel.org/process/submitting-patches.html#no-mime-no-links-no-compression-no-attachments-just-plain-text


On 1/15/25 15:24, 余华兵 wrote:
> The configuration file "kernel/Kconfig. preempt" says that PREEMPT_RT is 
> fully preemptible, but from the function preempt_model_full() it can be 
> seen that PREEMPT is full preemption model. -------------------------- 
> kernel/Kconfig.preempt config PREEMPT         bool "Preemptible Kernel 
> (Low-Latency Desktop)" config PREEMPT_RT         bool "Fully Preemptible 
> Kernel (Real-Time)" include/linux/preempt.h static inline bool 
> preempt_model_full(void) {         return IS_ENABLED(CONFIG_PREEMPT); } 
> -------------------------- 

On Preempt_RT kernel, the spinlocks are sleeping locks and irqs can run as threaded.
So even those can be preempted if necessary. That is not true with preempt=full alone.

I suggest that the configuration file
> "kernel/Kconfig. preempt" should be consistent with the function 
> preempt_model_full(). Modify the file "kernel/Kconfig.preempt" as 
> follows. ------------------ config PREEMPT         bool "Fully 
> Preemptible Kernel (Low-Latency Desktop)" config PREEMPT_RT         bool 
> "Real-time Kernel" ------------------