On Fri, May 21, 2021 at 12:05:27AM +0200, J Mårtensson wrote:

Hi, I have been trying to add a new scheduler to the Linux kernel. I have found that to add a sched_class, I need to add it to SCHED_DATA in vmlinux.lds.h. instead of editing the now removed .next variable. I'm assuming that you are referring to this patch from Steven Rostedt, right? https://lore.kernel.org/lkml/20191219214451.340746474@goodmis.org/

Depending on what order I put into the priority list, it will crash the kernel during the booting process after rebooting. Any tips on what could be causing this would be appreciated! I am not sure if I that would help, but if I were you I would try to isolate the problem with available debugging mechanisms available in the kernel. Have you tried compiling the kernel with CONFIG_SCHED_DEBUG=y and make use of Early Print K ?

https://www.kernel.org/doc/html/latest/x86/earlyprintk.html Since it's rebooting due to the error, you won't be able the see the logs... so if you enable early printk and get those messages across a piece of hardware that's not rebooting then at least you will be able to read those messages and add/rem statements to help you figure out what's going wrong. there is no silver-bullet solution for that, but I'm sure that you will have a lot of fun trying to debug this. Once you find the solution, please share with us. I'm sure this will be benefitial for future developers with similar questions.

Currently this works

#define SCHED_DATA \ STRUCT_ALIGN(); \ __begin_sched_classes = .; \ *(__idle_sched_class) \ *(__my_sched_class) \ *(__fair_sched_class) \ *(__rt_sched_class) \ *(__dl_sched_class) \ *(__stop_sched_class) \ __end_sched_classes = .;

This most likely works because during the OS booting, all processes executed have their scheduling needs sorted out from the dl_sched_class to the fair_sched_class. So either there is no moment when the CPU is idle throughout the process (unlikely) or the bug on your _my_sched_class isn't triggered when there is nothing in the CPU run queue. I can be wrong though, so if anyone has a better explanation, please chime in.

While this does not

#define SCHED_DATA \ STRUCT_ALIGN(); \ __begin_sched_classes = .; \ *(__idle_sched_class) \ *(__fair_sched_class) \ *(__my_sched_class) \ *(__rt_sched_class) \ *(__dl_sched_class) \ *(__stop_sched_class) \ __end_sched_classes = .;

It's hard to speculate about the reason why it's failing but if I was a gambling man I would say that *given the fact* that __my_sched_class has a higher-priority than the __fair_sched_class, it breaks when trying to execute the __my_sched_class methods defined in the DEFINE_SCHED_CLASS macro. Example from the fair.c sched class: https://github.com/torvalds/linux/blob/02dbb7246c5bbbbe1607ebdc546ba5c454a66... Paulo Miguel Almeida

Regards Jacob

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