Re: [PATCHSET sched_ext/for-7.5] sched_ext: scx_qmap: Drop the compat code and fix a lowpri starvation

[Andrea Righi]

On Mon, Oct 19, 2026 at 11:32:19AM -1000, Tejun Heo wrote:
> Hello,
> 
> scx_qmap is often used to exercise sched_ext features as they land and
> already requires the kernel it ships with, so its compat code only keeps
> untested fallbacks around. The first patch drops it.
> 
> The second fixes scx_qmap's lowpri path. Nice 19 tasks coming back from
> LOWPRI_DSQ go to SHARED_DSQ, which is consumed ahead of the FIFOs, so enough
> nice 19 CPU hogs starve every other task until the watchdog ejects the
> scheduler. They now go to their FIFO instead.
> 
> Tested with root and sub-scheduler instances under nice 0 and nice 19 CPU
> hogs. Without the fix, the root is ejected within seconds. With it, the runs
> complete and the FIFOs keep being dispatched.
> 
> Based on sched_ext/for-7.4-fixes (ff343a94e44d).
> 
> This patchset contains the following 2 patches.
> 
>  0001 sched_ext: scx_qmap: Drop the compat code
>  0002 sched_ext: scx_qmap: Queue re-enqueued lowpri tasks on their FIFO

Both look good to me.

Reviewed-by: Andrea Righi <arighi@xxxxxxxxxx>

Thanks,
-Andrea