Merge pull request #12 from sched-ext/scx_nest

scx_nest: Add scx_nest scheduler

Author: htejun

scheds/README.md

@@ -22,6 +22,8 @@ of schedulers:
   schedulers that are also shipped with the Linux kernel tree.
 - [rust-user](rust-user/README.md) describes all of the schedulers with rust
   user space components. All of these schedulers are production ready.
+- [c-user](c-user/README.md) describes all of the schedulers with C user space
+  components. All of these schedulers are production ready.
 
 ## Note on syncing
 

scheds/c-user/README.md

@@ -0,0 +1,43 @@
+EXAMPLE SCHEDULERS
+==================
+
+# Introduction
+
+This directory contains sched_ext schedulers with C user-space components.
+
+This document will give some background on each such scheduler, including
+describing the types of workloads or scenarios they're designed to accommodate.
+For more details on any of these schedulers, please see the header comment in
+their .bpf.c file.
+
+# Schedulers
+
+This section lists, in alphabetical order, all of the current example
+schedulers.
+
+--------------------------------------------------------------------------------
+
+## scx_nest
+
+### Overview
+
+A scheduler based on the following Inria-Paris paper: [OS Scheduling with Nest:
+Keeping Tasks Close Together on Warm
+Cores](https://hal.inria.fr/hal-03612592/file/paper.pdf). The core idea of the
+scheduler is to make scheduling decisions which encourage work to run on cores
+that are expected to have high frequency. This scheduler currently will only
+perform well on single CCX / single-socket hosts.
+
+### Typical Use Case
+
+scx_nest is designed to optimize workloads that CPU utilization somewhat low,
+and which can benefit from running on a subset of cores on the host so as to
+keep the frequencies high on those cores. Some workloads may perform better by
+spreading work across many cores to avoid thrashing the cache, etc. Determining
+whether a workload is well-suited to scx_nest will likely require
+expermentation.
+
+### Production Ready?
+
+This scheduler could be used in a production environment, assuming the hardware
+constraints enumerated above.

scheds/c-user/meson.build

@@ -0,0 +1,10 @@
+c_scheds = ['scx_nest']
+
+foreach sched: c_scheds
+  bpf_o = gen_bpf_o.process(sched + '.bpf.c', extra_args: bpf_includes)
+  bpf_skel = gen_bpf_skel.process(bpf_o)
+  executable(sched, [bpf_skel, sched + '.c'],
+             include_directories: [user_c_includes],
+             dependencies: libbpf_dep,
+             install: true)
+endforeach