From 9b671793c7d95f020791415cbbcc82b9c007d19c Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Fri, 27 Sep 2024 13:46:13 -1000
Subject: [PATCH] sched_ext, scx_qmap: Add and use SCX_ENQ_CPU_SELECTED
scx_qmap and other schedulers in the SCX repo are using SCX_ENQ_WAKEUP to
tell whether ops.select_cpu() was called. This is incorrect as
ops.select_cpu() can be skipped in the wakeup path and leads to e.g.
incorrectly skipping direct dispatch for tasks that are bound to a single
CPU.
sched core has been updated to specify ENQUEUE_RQ_SELECTED if
->select_task_rq() was called. Map it to SCX_ENQ_CPU_SELECTED and update
scx_qmap to test it instead of SCX_ENQ_WAKEUP.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>
Cc: Daniel Hodges <hodges.daniel.scott@gmail.com>
Cc: Changwoo Min <multics69@gmail.com>
Cc: Andrea Righi <andrea.righi@linux.dev>
Cc: Dan Schatzberg <schatzberg.dan@gmail.com>
---
kernel/sched/ext.c | 1 +
tools/sched_ext/scx_qmap.bpf.c | 4 ++--
2 files changed, 3 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 1df2082d1352e..410a4df8a121e 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -696,6 +696,7 @@ enum scx_enq_flags {
/* expose select ENQUEUE_* flags as enums */
SCX_ENQ_WAKEUP = ENQUEUE_WAKEUP,
SCX_ENQ_HEAD = ENQUEUE_HEAD,
+ SCX_ENQ_CPU_SELECTED = ENQUEUE_RQ_SELECTED,
/* high 32bits are SCX specific */
diff --git a/tools/sched_ext/scx_qmap.bpf.c b/tools/sched_ext/scx_qmap.bpf.c
index 67e2a7968cc91..5d1f880d1149e 100644
--- a/tools/sched_ext/scx_qmap.bpf.c
+++ b/tools/sched_ext/scx_qmap.bpf.c
@@ -230,8 +230,8 @@ void BPF_STRUCT_OPS(qmap_enqueue, struct task_struct *p, u64 enq_flags)
return;
}
- /* if !WAKEUP, select_cpu() wasn't called, try direct dispatch */
- if (!(enq_flags & SCX_ENQ_WAKEUP) &&
+ /* if select_cpu() wasn't called, try direct dispatch */
+ if (!(enq_flags & SCX_ENQ_CPU_SELECTED) &&
(cpu = pick_direct_dispatch_cpu(p, scx_bpf_task_cpu(p))) >= 0) {
__sync_fetch_and_add(&nr_ddsp_from_enq, 1);
scx_bpf_dispatch(p, SCX_DSQ_LOCAL_ON | cpu, slice_ns, enq_flags);
--
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