Commit 9b671793 authored Sep 27, 2024 by Tejun Heo

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>

parent f207dc2d

kernel/sched/ext.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -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 */

tools/sched_ext/scx_qmap.bpf.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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);