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

[Tejun Heo <tj@kernel.org>]

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

The patchset is also available in the following git branch:

 git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext.git qmap-nocompat

diffstat follows. Thanks.

 tools/sched_ext/scx_qmap.bpf.c | 40 +++++++++++++++++++++++-----------------
 tools/sched_ext/scx_qmap.c     | 14 +++++---------
 2 files changed, 28 insertions(+), 26 deletions(-)

--
tejun