sched_ext: Documentation: clarify arena-backed doubly-linked lists in scx_qmap

Update scx_qmap description to reflect arena-backed doubly-linked
lists with per-queue bpf_res_spin_lock.

Also update scx_qmap.bpf.c to reflect switch from PIDs to TIDs.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

Documentation/scheduler/sched-ext.rst

@@ -508,7 +508,7 @@ Where to Look
     custom DSQ.
 
   * ``scx_qmap[.bpf].c``: A multi-level FIFO scheduler supporting five
-    levels of priority implemented with ``BPF_MAP_TYPE_QUEUE``.
+    levels of priority implemented with arena-backed doubly-linked lists.
 
   * ``scx_central[.bpf].c``: A central FIFO scheduler where all scheduling
     decisions are made on one CPU, demonstrating ``LOCAL_ON`` dispatching,

tools/sched_ext/README.md

@@ -168,9 +168,9 @@ well on single-socket systems with a unified L3 cache.
 
 Another simple, yet slightly more complex scheduler that provides an example of
 a basic weighted FIFO queuing policy. It also provides examples of some common
-useful BPF features, such as sleepable per-task storage allocation in the
-`ops.prep_enable()` callback, and using the `BPF_MAP_TYPE_QUEUE` map type to
-enqueue tasks. It also illustrates how core-sched support could be implemented.
+useful BPF features, such as arena-backed doubly-linked lists threaded through
+per-task context and `bpf_res_spin_lock` for per-queue synchronization. It also
+illustrates how core-sched support could be implemented.
 
 ## scx_central
 

tools/sched_ext/scx_qmap.bpf.c

@@ -10,7 +10,7 @@
  *
  * This scheduler demonstrates:
  *
- * - BPF-side queueing using PIDs.
+ * - BPF-side queueing using TIDs.
  * - BPF arena for scheduler state.
  * - Core-sched support.
  *