On /usr/lib/sysctl.d/99-scylla-sched.conf, we have some sysctl settings to
tune the scheduler for lower latency.
This is mostly to prevent softirq threads processing tcp and reactor threads
from injecting latency into each other.
However, these parameters are moved to debugfs from linux-5.13+, so we lost
scheduler tuneing on recent kernels.
To support tuning recent kernel, let's add a new service which support
to configure both sysctl and debugfs.
The service named scylla-tune-sched.service
The service will unconditionally enables when installed, on older kernel
it will tune via sysctl, on recent kernel it will tune via debugfs.
Fixes#16077Closesscylladb/scylladb#16122
6eb9344cb3