scx_loader: add support for global flags across all scheduling modes

[mnixry]

Currently, scx_loader allows custom flags to be specified for each mode, but lacks the ability to apply common flags across all modes. This would be particularly useful for monitoring options like --stats that are commonly supported by most schedulers.

I propose adding support for additional flags that would be applied regardless of the selected mode. This would enable users to monitor scheduler statistics in real-time by tailing the scx_loader log, independent of the current operating mode.

Here are two possible implementation approaches:

default_sched = "scx_bpfland"
default_mode = "Auto"
+ default_additional_flag = ["--stats", "5"] # Option 1: Global configuration

[scheds.scx_bpfland]
auto_mode = []
gaming_mode = ["-m", "performance"]
lowlatency_mode = ["-k", "-s", "5000", "-l", "5000"]
powersave_mode = ["-m", "powersave"]
+ default_additional_flag = ["--stats", "5"] # Option 2: Scheduler-specific configuration

I'm willing to implement either approach if there's interest in this feature.

[vnepogodin]

Currently, scx_loader allows custom flags to be specified for each mode, but lacks the ability to apply common flags across all modes. This would be particularly useful for monitoring options like --stats that are commonly supported by most schedulers.

I propose adding support for additional flags that would be applied regardless of the selected mode. This would enable users to monitor scheduler statistics in real-time by tailing the scx_loader log, independent of the current operating mode.

Here are two possible implementation approaches:

default_sched = "scx_bpfland"
default_mode = "Auto"
+ default_additional_flag = ["--stats", "5"] # Option 1: Global configuration

[scheds.scx_bpfland]
auto_mode = []
gaming_mode = ["-m", "performance"]
lowlatency_mode = ["-k", "-s", "5000", "-l", "5000"]
powersave_mode = ["-m", "powersave"]
+ default_additional_flag = ["--stats", "5"] # Option 2: Scheduler-specific configuration

I'm willing to implement either approach if there's interest in this feature.

I think first option would make more sense here.

As for the statistics(For debugging), I think instead of adding new configuration option it would also make sense to add new method to "enable debug mode" 🤔

[mnixry]

I think first option would make more sense here.

As for the statistics(For debugging), I think instead of adding new configuration option it would also make sense to add new method to "enable debug mode" 🤔

Thank you for your reply.

Based on your proposal, it seems feasible to have additional flags directly passed to any scheduler launched by scx_loader. For instance, using scx_loader -- --debug --stats 5 would pass all arguments after -- to the scheduler, making the global flag solution possible.

I personally prefer the configuration file solution because the flag-passing approach might require overlaying SystemD unit config file to make adjustments, which doesn't seem like a very elegant solution for me.

Furthermore, There is the possibility that some scheduler extensions in future might not support certain global flags we specify. This could cause them to crash if inappropriate flags are passed, which would be inconvenient, especially when making changes over DBus.

---

BTW, I'm very new to the sched_ext feature of the kernel, so I wonder if the statistics flag should only be used in the case of debugging (maybe due to potential performance impacts or other reasons)?

[hodgesds]

FYI you can also run the scheduler binaries with --monitor <interval> to print stats from a running scheduler (even if the scheduler isn't running with --stats <interval).

so I wonder if the statistics flag should only be used in the case of debugging (maybe due to potential performance impacts or other reasons)?

Should be fine, it's similar to any other type of log.