[PATCH 14/17] tools/sched_ext: scx_qmap: Restart on hotplug instead of cpu_online/offline

[PATCH 14/17] tools/sched_ext: scx_qmap: Restart on hotplug instead of cpu_online/offline

[Tejun Heo]

The cid mapping is built from the online cpu set at scheduler enable
and stays valid for that set; routine hotplug invalidates it. The
default cid behavior is to restart the scheduler so the mapping gets
rebuilt against the new online set, and that requires not implementing
cpu_online / cpu_offline (which suppress the kernel's ACT_RESTART).

Drop the two ops along with their print_cpus() helper - the cluster
view was only useful as a hotplug demo and is meaningless over the
dense cid space the scheduler will move to. Wire main() to handle the
ACT_RESTART exit by reopening the skel and reattaching, matching the
pattern in scx_simple / scx_central / scx_flatcg etc. Reset optind so
getopt re-parses argv into the fresh skel rodata each iteration.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
---
 tools/sched_ext/scx_qmap.bpf.c | 62 ----------------------------------
 tools/sched_ext/scx_qmap.c     | 13 +++----
 2 files changed, 7 insertions(+), 68 deletions(-)

diff --git a/tools/sched_ext/scx_qmap.bpf.c b/tools/sched_ext/scx_qmap.bpf.c
index ba4879031dac..78a1dd118c7e 100644
--- a/tools/sched_ext/scx_qmap.bpf.c
+++ b/tools/sched_ext/scx_qmap.bpf.c
@@ -843,63 +843,6 @@ void BPF_STRUCT_OPS(qmap_cgroup_set_bandwidth, struct cgroup *cgrp,
 			   cgrp->kn->id, period_us, quota_us, burst_us);
 }
 
-/*
- * Print out the online and possible CPU map using bpf_printk() as a
- * demonstration of using the cpumask kfuncs and ops.cpu_on/offline().
- */
-static void print_cpus(void)
-{
-	const struct cpumask *possible, *online;
-	s32 cpu;
-	char buf[128] = "", *p;
-	int idx;
-
-	possible = scx_bpf_get_possible_cpumask();
-	online = scx_bpf_get_online_cpumask();
-
-	idx = 0;
-	bpf_for(cpu, 0, scx_bpf_nr_cpu_ids()) {
-		if (!(p = MEMBER_VPTR(buf, [idx++])))
-			break;
-		if (bpf_cpumask_test_cpu(cpu, online))
-			*p++ = 'O';
-		else if (bpf_cpumask_test_cpu(cpu, possible))
-			*p++ = 'X';
-		else
-			*p++ = ' ';
-
-		if ((cpu & 7) == 7) {
-			if (!(p = MEMBER_VPTR(buf, [idx++])))
-				break;
-			*p++ = '|';
-		}
-	}
-	buf[sizeof(buf) - 1] = '\0';
-
-	scx_bpf_put_cpumask(online);
-	scx_bpf_put_cpumask(possible);
-
-	bpf_printk("CPUS: |%s", buf);
-}
-
-void BPF_STRUCT_OPS(qmap_cpu_online, s32 cpu)
-{
-	if (print_msgs) {
-		bpf_printk("CPU %d coming online", cpu);
-		/* @cpu is already online at this point */
-		print_cpus();
-	}
-}
-
-void BPF_STRUCT_OPS(qmap_cpu_offline, s32 cpu)
-{
-	if (print_msgs) {
-		bpf_printk("CPU %d going offline", cpu);
-		/* @cpu is still online at this point */
-		print_cpus();
-	}
-}
-
 struct monitor_timer {
 	struct bpf_timer timer;
 };
@@ -1078,9 +1021,6 @@ s32 BPF_STRUCT_OPS_SLEEPABLE(qmap_init)
 		slab[i].next_free = (i + 1 < max_tasks) ? &slab[i + 1] : NULL;
 	qa.task_free_head = &slab[0];
 
-	if (print_msgs && !sub_cgroup_id)
-		print_cpus();
-
 	ret = scx_bpf_create_dsq(SHARED_DSQ, -1);
 	if (ret) {
 		scx_bpf_error("failed to create DSQ %d (%d)", SHARED_DSQ, ret);
@@ -1174,8 +1114,6 @@ SCX_OPS_DEFINE(qmap_ops,
 	       .cgroup_set_bandwidth	= (void *)qmap_cgroup_set_bandwidth,
 	       .sub_attach		= (void *)qmap_sub_attach,
 	       .sub_detach		= (void *)qmap_sub_detach,
-	       .cpu_online		= (void *)qmap_cpu_online,
-	       .cpu_offline		= (void *)qmap_cpu_offline,
 	       .init			= (void *)qmap_init,
 	       .exit			= (void *)qmap_exit,
 	       .timeout_ms		= 5000U,
diff --git a/tools/sched_ext/scx_qmap.c b/tools/sched_ext/scx_qmap.c
index 725c4880058d..99408b1bb1ec 100644
--- a/tools/sched_ext/scx_qmap.c
+++ b/tools/sched_ext/scx_qmap.c
@@ -67,12 +67,14 @@ int main(int argc, char **argv)
 	struct bpf_link *link;
 	struct qmap_arena *qa;
 	__u32 test_error_cnt = 0;
+	__u64 ecode;
 	int opt;
 
 	libbpf_set_print(libbpf_print_fn);
 	signal(SIGINT, sigint_handler);
 	signal(SIGTERM, sigint_handler);
-
+restart:
+	optind = 1;
 	skel = SCX_OPS_OPEN(qmap_ops, scx_qmap);
 
 	skel->rodata->slice_ns = __COMPAT_ENUM_OR_ZERO("scx_public_consts", "SCX_SLICE_DFL");
@@ -184,11 +186,10 @@ int main(int argc, char **argv)
 	}
 
 	bpf_link__destroy(link);
-	UEI_REPORT(skel, uei);
+	ecode = UEI_REPORT(skel, uei);
 	scx_qmap__destroy(skel);
-	/*
-	 * scx_qmap implements ops.cpu_on/offline() and doesn't need to restart
-	 * on CPU hotplug events.
-	 */
+
+	if (UEI_ECODE_RESTART(ecode))
+		goto restart;
 	return 0;
 }
-- 
2.53.0

[PATCHSET v2 REPOST sched_ext/for-7.2] sched_ext: Topological CPU IDs and cid-form struct_ops

[Tejun Heo]

Hello,

Reposting v2 because the original send was not properly threaded -
each patch went out as a standalone top-level message. Content is
unchanged from the original v2.

Original v2: https://lore.kernel.org/r/20260424013220.2923402-1-tj@kernel.org

v2 of https://lore.kernel.org/r/20260421071945.3110084-1-tj@kernel.org

v2:
- Add ext-types.h first patch for early subsystem-wide type defs.
- cid: publish the cid tables with WRITE_ONCE / read with READ_ONCE;
  document the visibility contract.
- cid-kfuncs: NULL-guard scx_bpf_this_cid / scx_bpf_task_cid for
  TRACING/SYSCALL callers before any SCX sched has enabled.
- cid-struct-ops: use struct_size() for the set_cmask_scratch percpu
  alloc; cluster __scx_is_cid_type disable with __scx_enabled disable
  in scx_root_disable().
- cid-kfunc-filter: sync per-entry kfunc flags with each kfunc's
  primary BTF_ID_FLAGS() declaration (Zhao). pahole intersects flags
  across occurrences; omitting them drops the flags globally - the
  visible symptom was KF_IMPLICIT_ARGS getting cleared on
  scx_bpf_kick_cpu, leaking bpf_prog_aux into vmlinux.h.
- cmask: narrow to the helpers this series actually uses;
  cmask_copy_from_kernel contract and runtime guard.

This patchset introduces topological CPU IDs (cids) - dense,
topology-ordered cpu identifiers - and an alternative cid-form struct_ops
type that lets BPF schedulers operate in cid space directly.

Key pieces:

- cid space: scx_cid_init() walks nodes * LLCs * cores * threads and packs
  a dense cid mapping. The mapping can be overridden via
  scx_bpf_cid_override(). See "Topological CPU IDs" in ext_cid.h for the
  model.

- cmask: a base-windowed bitmap over cid space. Kernel and BPF helpers with
  identical semantics. Used by scx_qmap for per-task affinity and idle-cid
  tracking; meant to be the substrate for sub-sched cid allocation.

- bpf_sched_ext_ops_cid: a parallel struct_ops type whose callbacks take
  cids/cmasks instead of cpus/cpumasks. Kernel translates at the boundary
  via scx_cpu_arg() / scx_cpu_ret(); the two struct types share offsets up
  through @priv (verified by BUILD_BUG_ON) so the union view in scx_sched
  works without function-pointer casts. Sub-sched support is tied to
  cid-form: validate_ops() rejects cpu-form sub-scheds and cpu-form roots
  that expose sub_attach / sub_detach.

- cid-form kfuncs: scx_bpf_kick_cid, scx_bpf_cidperf_{cap,cur,set},
  scx_bpf_cid_curr, scx_bpf_task_cid, scx_bpf_this_cid,
  scx_bpf_nr_{cids,online_cids}, scx_bpf_cid_to_cpu, scx_bpf_cpu_to_cid.
  A cid-form program may not call cpu-only kfuncs (enforced at verifier
  load via scx_kfunc_context_filter); the reverse is intentionally
  permissive to ease migration.

- scx_qmap port: scx_qmap is converted to cid-form. It uses the cmask-based
  idle picker, per-task cid-space cpus_allowed, and cid-form kfuncs
  throughout. Sub-sched dispatching via scx_bpf_sub_dispatch() continues to
  work.

v2 re-tested on the 16-cpu QEMU: cid-form scx_qmap, cpu-form scx_simple,
cid<->cpu cycling, scx_qmap under stress-ng, hotplug auto-restart, and
sub-sched (root scx_qmap + cgroup-scoped scx_qmap child). Clean.

Based on sched_ext/for-7.2 (c2929bc21dce).

 0001-sched_ext-Add-ext_types.h-for-early-subsystem-wide-d.patch
 0002-sched_ext-Rename-ops_cpu_valid-to-scx_cpu_valid-and-.patch
 0003-sched_ext-Move-scx_exit-scx_error-and-friends-to-ext.patch
 0004-sched_ext-Shift-scx_kick_cpu-validity-check-to-scx_b.patch
 0005-sched_ext-Relocate-cpu_acquire-cpu_release-to-end-of.patch
 0006-sched_ext-Make-scx_enable-take-scx_enable_cmd.patch
 0007-sched_ext-Add-topological-CPU-IDs-cids.patch
 0008-sched_ext-Add-scx_bpf_cid_override-kfunc.patch
 0009-tools-sched_ext-Add-struct_size-helpers-to-common.bp.patch
 0010-sched_ext-Add-cmask-a-base-windowed-bitmap-over-cid-.patch
 0011-sched_ext-Add-cid-form-kfunc-wrappers-alongside-cpu-.patch
 0012-sched_ext-Add-bpf_sched_ext_ops_cid-struct_ops-type.patch
 0013-sched_ext-Forbid-cpu-form-kfuncs-from-cid-form-sched.patch
 0014-tools-sched_ext-scx_qmap-Restart-on-hotplug-instead-.patch
 0015-tools-sched_ext-scx_qmap-Add-cmask-based-idle-tracki.patch
 0016-tools-sched_ext-scx_qmap-Port-to-cid-form-struct_ops.patch
 0017-sched_ext-Require-cid-form-struct_ops-for-sub-sched-.patch

Git tree: git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext.git scx-cid-v2

 kernel/sched/build_policy.c              |   2 +
 kernel/sched/ext.c                       | 650 +++++++++++++++++++++++++----
 kernel/sched/ext_cid.c                   | 417 ++++++++++++++++++++
 kernel/sched/ext_cid.h                   | 164 ++++++++
 kernel/sched/ext_idle.c                  |   8 +-
 kernel/sched/ext_internal.h              | 203 +++++++---
 kernel/sched/ext_types.h                 | 104 +++++
 tools/sched_ext/include/scx/cid.bpf.h    | 597 ++++++++++++++++++++++++++++
 tools/sched_ext/include/scx/common.bpf.h |  23 ++
 tools/sched_ext/include/scx/compat.bpf.h |  24 ++
 tools/sched_ext/scx_qmap.bpf.c           | 306 ++++++++-------
 tools/sched_ext/scx_qmap.c               |  25 +-
 tools/sched_ext/scx_qmap.h               |   2 +-
 13 files changed, 2240 insertions(+), 285 deletions(-)

--
tejun

[PATCH 14/17] tools/sched_ext: scx_qmap: Restart on hotplug instead of cpu_online/offline

[Tejun Heo]

The cid mapping is built from the online cpu set at scheduler enable
and stays valid for that set; routine hotplug invalidates it. The
default cid behavior is to restart the scheduler so the mapping gets
rebuilt against the new online set, and that requires not implementing
cpu_online / cpu_offline (which suppress the kernel's ACT_RESTART).

Drop the two ops along with their print_cpus() helper - the cluster
view was only useful as a hotplug demo and is meaningless over the
dense cid space the scheduler will move to. Wire main() to handle the
ACT_RESTART exit by reopening the skel and reattaching, matching the
pattern in scx_simple / scx_central / scx_flatcg etc. Reset optind so
getopt re-parses argv into the fresh skel rodata each iteration.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
---
 tools/sched_ext/scx_qmap.bpf.c | 62 ----------------------------------
 tools/sched_ext/scx_qmap.c     | 13 +++----
 2 files changed, 7 insertions(+), 68 deletions(-)

diff --git a/tools/sched_ext/scx_qmap.bpf.c b/tools/sched_ext/scx_qmap.bpf.c
index ba4879031dac..78a1dd118c7e 100644
--- a/tools/sched_ext/scx_qmap.bpf.c
+++ b/tools/sched_ext/scx_qmap.bpf.c
@@ -843,63 +843,6 @@ void BPF_STRUCT_OPS(qmap_cgroup_set_bandwidth, struct cgroup *cgrp,
 			   cgrp->kn->id, period_us, quota_us, burst_us);
 }
 
-/*
- * Print out the online and possible CPU map using bpf_printk() as a
- * demonstration of using the cpumask kfuncs and ops.cpu_on/offline().
- */
-static void print_cpus(void)
-{
-	const struct cpumask *possible, *online;
-	s32 cpu;
-	char buf[128] = "", *p;
-	int idx;
-
-	possible = scx_bpf_get_possible_cpumask();
-	online = scx_bpf_get_online_cpumask();
-
-	idx = 0;
-	bpf_for(cpu, 0, scx_bpf_nr_cpu_ids()) {
-		if (!(p = MEMBER_VPTR(buf, [idx++])))
-			break;
-		if (bpf_cpumask_test_cpu(cpu, online))
-			*p++ = 'O';
-		else if (bpf_cpumask_test_cpu(cpu, possible))
-			*p++ = 'X';
-		else
-			*p++ = ' ';
-
-		if ((cpu & 7) == 7) {
-			if (!(p = MEMBER_VPTR(buf, [idx++])))
-				break;
-			*p++ = '|';
-		}
-	}
-	buf[sizeof(buf) - 1] = '\0';
-
-	scx_bpf_put_cpumask(online);
-	scx_bpf_put_cpumask(possible);
-
-	bpf_printk("CPUS: |%s", buf);
-}
-
-void BPF_STRUCT_OPS(qmap_cpu_online, s32 cpu)
-{
-	if (print_msgs) {
-		bpf_printk("CPU %d coming online", cpu);
-		/* @cpu is already online at this point */
-		print_cpus();
-	}
-}
-
-void BPF_STRUCT_OPS(qmap_cpu_offline, s32 cpu)
-{
-	if (print_msgs) {
-		bpf_printk("CPU %d going offline", cpu);
-		/* @cpu is still online at this point */
-		print_cpus();
-	}
-}
-
 struct monitor_timer {
 	struct bpf_timer timer;
 };
@@ -1078,9 +1021,6 @@ s32 BPF_STRUCT_OPS_SLEEPABLE(qmap_init)
 		slab[i].next_free = (i + 1 < max_tasks) ? &slab[i + 1] : NULL;
 	qa.task_free_head = &slab[0];
 
-	if (print_msgs && !sub_cgroup_id)
-		print_cpus();
-
 	ret = scx_bpf_create_dsq(SHARED_DSQ, -1);
 	if (ret) {
 		scx_bpf_error("failed to create DSQ %d (%d)", SHARED_DSQ, ret);
@@ -1174,8 +1114,6 @@ SCX_OPS_DEFINE(qmap_ops,
 	       .cgroup_set_bandwidth	= (void *)qmap_cgroup_set_bandwidth,
 	       .sub_attach		= (void *)qmap_sub_attach,
 	       .sub_detach		= (void *)qmap_sub_detach,
-	       .cpu_online		= (void *)qmap_cpu_online,
-	       .cpu_offline		= (void *)qmap_cpu_offline,
 	       .init			= (void *)qmap_init,
 	       .exit			= (void *)qmap_exit,
 	       .timeout_ms		= 5000U,
diff --git a/tools/sched_ext/scx_qmap.c b/tools/sched_ext/scx_qmap.c
index 725c4880058d..99408b1bb1ec 100644
--- a/tools/sched_ext/scx_qmap.c
+++ b/tools/sched_ext/scx_qmap.c
@@ -67,12 +67,14 @@ int main(int argc, char **argv)
 	struct bpf_link *link;
 	struct qmap_arena *qa;
 	__u32 test_error_cnt = 0;
+	__u64 ecode;
 	int opt;
 
 	libbpf_set_print(libbpf_print_fn);
 	signal(SIGINT, sigint_handler);
 	signal(SIGTERM, sigint_handler);
-
+restart:
+	optind = 1;
 	skel = SCX_OPS_OPEN(qmap_ops, scx_qmap);
 
 	skel->rodata->slice_ns = __COMPAT_ENUM_OR_ZERO("scx_public_consts", "SCX_SLICE_DFL");
@@ -184,11 +186,10 @@ int main(int argc, char **argv)
 	}
 
 	bpf_link__destroy(link);
-	UEI_REPORT(skel, uei);
+	ecode = UEI_REPORT(skel, uei);
 	scx_qmap__destroy(skel);
-	/*
-	 * scx_qmap implements ops.cpu_on/offline() and doesn't need to restart
-	 * on CPU hotplug events.
-	 */
+
+	if (UEI_ECODE_RESTART(ecode))
+		goto restart;
 	return 0;
 }
-- 
2.53.0

[PATCHSET v3 sched_ext/for-7.2] sched_ext: Topological CPU IDs and cid-form struct_ops

[Tejun Heo]

Hello,

v3 (all from the Sashiko AI review at
https://sashiko.dev/#/patchset/20260424172721.3458520-1-tj%40kernel.org):

- cid: drop leaked cpus_read_lock() on scx_cid_init() failure;
  BUILD_BUG_ON tightened to NR_CPUS<=8192 to match the BPF cmask
  helpers' CMASK_MAX_WORDS coverage.
- bpf-struct-size: use offsetof() in struct_size() to match the
  kernel <linux/overflow.h> macro semantics (no inflation from
  trailing struct padding).
- cmask: cmask_copy_from_kernel() validates src->base==0 via
  probe-read; nr_bits check is bit-level rather than rounded-up
  word-count.
- cid-qmap-idle: qmap_init() refuses to load when scx_bpf_nr_cids()
  exceeds SCX_QMAP_MAX_CPUS; the task_ctx flex array would otherwise
  overflow into the next slab entry.

v2: https://lore.kernel.org/r/20260424172721.3458520-1-tj@kernel.org
v1: https://lore.kernel.org/r/20260421071945.3110084-1-tj@kernel.org

This patchset introduces topological CPU IDs (cids) - dense,
topology-ordered cpu identifiers - and an alternative cid-form struct_ops
type that lets BPF schedulers operate in cid space directly.

Key pieces:

- cid space: scx_cid_init() walks nodes * LLCs * cores * threads and packs
  a dense cid mapping. The mapping can be overridden via
  scx_bpf_cid_override(). See "Topological CPU IDs" in ext_cid.h for the
  model.

- cmask: a base-windowed bitmap over cid space. Kernel and BPF helpers with
  identical semantics. Used by scx_qmap for per-task affinity and idle-cid
  tracking; meant to be the substrate for sub-sched cid allocation.

- bpf_sched_ext_ops_cid: a parallel struct_ops type whose callbacks take
  cids/cmasks instead of cpus/cpumasks. Kernel translates at the boundary
  via scx_cpu_arg() / scx_cpu_ret(); the two struct types share offsets up
  through @priv (verified by BUILD_BUG_ON) so the union view in scx_sched
  works without function-pointer casts. Sub-sched support is tied to
  cid-form: validate_ops() rejects cpu-form sub-scheds and cpu-form roots
  that expose sub_attach / sub_detach.

- cid-form kfuncs: scx_bpf_kick_cid, scx_bpf_cidperf_{cap,cur,set},
  scx_bpf_cid_curr, scx_bpf_task_cid, scx_bpf_this_cid,
  scx_bpf_nr_{cids,online_cids}, scx_bpf_cid_to_cpu, scx_bpf_cpu_to_cid.
  A cid-form program may not call cpu-only kfuncs (enforced at verifier
  load via scx_kfunc_context_filter); the reverse is intentionally
  permissive to ease migration.

- scx_qmap port: scx_qmap is converted to cid-form. It uses the cmask-based
  idle picker, per-task cid-space cpus_allowed, and cid-form kfuncs
  throughout. Sub-sched dispatching via scx_bpf_sub_dispatch() continues to
  work.

v3 re-tested on the 16-cpu QEMU: cid-form scx_qmap under stress-ng plus
reload cycles, hotplug auto-restart, and sub-sched (root scx_qmap +
cgroup-scoped scx_qmap child). Clean.

Based on sched_ext/for-7.2 (4939721aad2e).

 0001-sched_ext-Add-ext_types.h-for-early-subsystem-wide-d.patch
 0002-sched_ext-Rename-ops_cpu_valid-to-scx_cpu_valid-and-.patch
 0003-sched_ext-Move-scx_exit-scx_error-and-friends-to-ext.patch
 0004-sched_ext-Shift-scx_kick_cpu-validity-check-to-scx_b.patch
 0005-sched_ext-Relocate-cpu_acquire-cpu_release-to-end-of.patch
 0006-sched_ext-Make-scx_enable-take-scx_enable_cmd.patch
 0007-sched_ext-Add-topological-CPU-IDs-cids.patch
 0008-sched_ext-Add-scx_bpf_cid_override-kfunc.patch
 0009-tools-sched_ext-Add-struct_size-helpers-to-common.bp.patch
 0010-sched_ext-Add-cmask-a-base-windowed-bitmap-over-cid-.patch
 0011-sched_ext-Add-cid-form-kfunc-wrappers-alongside-cpu-.patch
 0012-sched_ext-Add-bpf_sched_ext_ops_cid-struct_ops-type.patch
 0013-sched_ext-Forbid-cpu-form-kfuncs-from-cid-form-sched.patch
 0014-tools-sched_ext-scx_qmap-Restart-on-hotplug-instead-.patch
 0015-tools-sched_ext-scx_qmap-Add-cmask-based-idle-tracki.patch
 0016-tools-sched_ext-scx_qmap-Port-to-cid-form-struct_ops.patch
 0017-sched_ext-Require-cid-form-struct_ops-for-sub-sched-.patch

Git tree: git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext.git scx-cid-v3

 kernel/sched/build_policy.c              |   3 +
 kernel/sched/ext.c                       | 651 ++++++++++++++++++++++++++----
 kernel/sched/ext_cid.c                   | 409 +++++++++++++++++++
 kernel/sched/ext_cid.h                   | 164 ++++++++
 kernel/sched/ext_idle.c                  |   8 +-
 kernel/sched/ext_internal.h              | 205 +++++++---
 kernel/sched/ext_types.h                 | 104 +++++
 tools/sched_ext/include/scx/cid.bpf.h    | 667 +++++++++++++++++++++++++++++++
 tools/sched_ext/include/scx/common.bpf.h |  23 ++
 tools/sched_ext/include/scx/compat.bpf.h |  24 ++
 tools/sched_ext/scx_qmap.bpf.c           | 346 +++++++++-------
 tools/sched_ext/scx_qmap.c               |  70 +++-
 tools/sched_ext/scx_qmap.h               |   2 +-
 13 files changed, 2391 insertions(+), 285 deletions(-)

Thanks.

--
tejun

[PATCH 14/17] tools/sched_ext: scx_qmap: Restart on hotplug instead of cpu_online/offline

[Tejun Heo]

The cid mapping is built from the online cpu set at scheduler enable
and stays valid for that set; routine hotplug invalidates it. The
default cid behavior is to restart the scheduler so the mapping gets
rebuilt against the new online set, and that requires not implementing
cpu_online / cpu_offline (which suppress the kernel's ACT_RESTART).

Drop the two ops along with their print_cpus() helper - the cluster
view was only useful as a hotplug demo and is meaningless over the
dense cid space the scheduler will move to. Wire main() to handle the
ACT_RESTART exit by reopening the skel and reattaching, matching the
pattern in scx_simple / scx_central / scx_flatcg etc. Reset optind so
getopt re-parses argv into the fresh skel rodata each iteration.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
---
 tools/sched_ext/scx_qmap.bpf.c | 62 ----------------------------------
 tools/sched_ext/scx_qmap.c     | 13 +++----
 2 files changed, 7 insertions(+), 68 deletions(-)

diff --git a/tools/sched_ext/scx_qmap.bpf.c b/tools/sched_ext/scx_qmap.bpf.c
index ba4879031dac..78a1dd118c7e 100644
--- a/tools/sched_ext/scx_qmap.bpf.c
+++ b/tools/sched_ext/scx_qmap.bpf.c
@@ -843,63 +843,6 @@ void BPF_STRUCT_OPS(qmap_cgroup_set_bandwidth, struct cgroup *cgrp,
 			   cgrp->kn->id, period_us, quota_us, burst_us);
 }
 
-/*
- * Print out the online and possible CPU map using bpf_printk() as a
- * demonstration of using the cpumask kfuncs and ops.cpu_on/offline().
- */
-static void print_cpus(void)
-{
-	const struct cpumask *possible, *online;
-	s32 cpu;
-	char buf[128] = "", *p;
-	int idx;
-
-	possible = scx_bpf_get_possible_cpumask();
-	online = scx_bpf_get_online_cpumask();
-
-	idx = 0;
-	bpf_for(cpu, 0, scx_bpf_nr_cpu_ids()) {
-		if (!(p = MEMBER_VPTR(buf, [idx++])))
-			break;
-		if (bpf_cpumask_test_cpu(cpu, online))
-			*p++ = 'O';
-		else if (bpf_cpumask_test_cpu(cpu, possible))
-			*p++ = 'X';
-		else
-			*p++ = ' ';
-
-		if ((cpu & 7) == 7) {
-			if (!(p = MEMBER_VPTR(buf, [idx++])))
-				break;
-			*p++ = '|';
-		}
-	}
-	buf[sizeof(buf) - 1] = '\0';
-
-	scx_bpf_put_cpumask(online);
-	scx_bpf_put_cpumask(possible);
-
-	bpf_printk("CPUS: |%s", buf);
-}
-
-void BPF_STRUCT_OPS(qmap_cpu_online, s32 cpu)
-{
-	if (print_msgs) {
-		bpf_printk("CPU %d coming online", cpu);
-		/* @cpu is already online at this point */
-		print_cpus();
-	}
-}
-
-void BPF_STRUCT_OPS(qmap_cpu_offline, s32 cpu)
-{
-	if (print_msgs) {
-		bpf_printk("CPU %d going offline", cpu);
-		/* @cpu is still online at this point */
-		print_cpus();
-	}
-}
-
 struct monitor_timer {
 	struct bpf_timer timer;
 };
@@ -1078,9 +1021,6 @@ s32 BPF_STRUCT_OPS_SLEEPABLE(qmap_init)
 		slab[i].next_free = (i + 1 < max_tasks) ? &slab[i + 1] : NULL;
 	qa.task_free_head = &slab[0];
 
-	if (print_msgs && !sub_cgroup_id)
-		print_cpus();
-
 	ret = scx_bpf_create_dsq(SHARED_DSQ, -1);
 	if (ret) {
 		scx_bpf_error("failed to create DSQ %d (%d)", SHARED_DSQ, ret);
@@ -1174,8 +1114,6 @@ SCX_OPS_DEFINE(qmap_ops,
 	       .cgroup_set_bandwidth	= (void *)qmap_cgroup_set_bandwidth,
 	       .sub_attach		= (void *)qmap_sub_attach,
 	       .sub_detach		= (void *)qmap_sub_detach,
-	       .cpu_online		= (void *)qmap_cpu_online,
-	       .cpu_offline		= (void *)qmap_cpu_offline,
 	       .init			= (void *)qmap_init,
 	       .exit			= (void *)qmap_exit,
 	       .timeout_ms		= 5000U,
diff --git a/tools/sched_ext/scx_qmap.c b/tools/sched_ext/scx_qmap.c
index 725c4880058d..99408b1bb1ec 100644
--- a/tools/sched_ext/scx_qmap.c
+++ b/tools/sched_ext/scx_qmap.c
@@ -67,12 +67,14 @@ int main(int argc, char **argv)
 	struct bpf_link *link;
 	struct qmap_arena *qa;
 	__u32 test_error_cnt = 0;
+	__u64 ecode;
 	int opt;
 
 	libbpf_set_print(libbpf_print_fn);
 	signal(SIGINT, sigint_handler);
 	signal(SIGTERM, sigint_handler);
-
+restart:
+	optind = 1;
 	skel = SCX_OPS_OPEN(qmap_ops, scx_qmap);
 
 	skel->rodata->slice_ns = __COMPAT_ENUM_OR_ZERO("scx_public_consts", "SCX_SLICE_DFL");
@@ -184,11 +186,10 @@ int main(int argc, char **argv)
 	}
 
 	bpf_link__destroy(link);
-	UEI_REPORT(skel, uei);
+	ecode = UEI_REPORT(skel, uei);
 	scx_qmap__destroy(skel);
-	/*
-	 * scx_qmap implements ops.cpu_on/offline() and doesn't need to restart
-	 * on CPU hotplug events.
-	 */
+
+	if (UEI_ECODE_RESTART(ecode))
+		goto restart;
 	return 0;
 }
-- 
2.54.0