@@ -7984,6 +7984,8 @@ int sched_cpu_activate(unsigned int cpu)
cpuset_cpu_active();
}
+ scx_rq_activate(rq);
+
/*
* Put the rq online, if not already. This happens:
*
@@ -8044,6 +8046,8 @@ int sched_cpu_deactivate(unsigned int cpu)
}
rq_unlock_irqrestore(rq, &rf);
+ scx_rq_deactivate(rq);
+
#ifdef CONFIG_SCHED_SMT
/*
* When going down, decrement the number of cores with SMT present.
@@ -30,6 +30,29 @@ enum scx_exit_kind {
SCX_EXIT_ERROR_STALL, /* watchdog detected stalled runnable tasks */
};
+/*
+ * An exit code can be specified when exiting with scx_bpf_exit() or
+ * scx_ops_exit(), corresponding to exit_kind UNREG_BPF and UNREG_KERN
+ * respectively. The codes are 64bit of the format:
+ *
+ * Bits: [63 .. 48 47 .. 32 31 .. 0]
+ * [ SYS ACT ] [ SYS RSN ] [ USR ]
+ *
+ * SYS ACT: System-defined exit actions
+ * SYS RSN: System-defined exit reasons
+ * USR : User-defined exit codes and reasons
+ *
+ * Using the above, users may communicate intention and context by ORing system
+ * actions and/or system reasons with a user-defined exit code.
+ */
+enum scx_exit_code {
+ /* Reasons */
+ SCX_ECODE_RSN_HOTPLUG = 1LLU << 32,
+
+ /* Actions */
+ SCX_ECODE_ACT_RESTART = 1LLU << 48,
+};
+
/*
* scx_exit_info is passed to ops.exit() to describe why the BPF scheduler is
* being disabled.
@@ -457,7 +480,29 @@ struct sched_ext_ops {
void (*dump_task)(struct scx_dump_ctx *ctx, struct task_struct *p);
/*
- * All online ops must come before ops.init().
+ * All online ops must come before ops.cpu_online().
+ */
+
+ /**
+ * cpu_online - A CPU became online
+ * @cpu: CPU which just came up
+ *
+ * @cpu just came online. @cpu will not call ops.enqueue() or
+ * ops.dispatch(), nor run tasks associated with other CPUs beforehand.
+ */
+ void (*cpu_online)(s32 cpu);
+
+ /**
+ * cpu_offline - A CPU is going offline
+ * @cpu: CPU which is going offline
+ *
+ * @cpu is going offline. @cpu will not call ops.enqueue() or
+ * ops.dispatch(), nor run tasks associated with other CPUs afterwards.
+ */
+ void (*cpu_offline)(s32 cpu);
+
+ /*
+ * All CPU hotplug ops must come before ops.init().
*/
/**
@@ -496,6 +541,15 @@ struct sched_ext_ops {
*/
u32 exit_dump_len;
+ /**
+ * hotplug_seq - A sequence number that may be set by the scheduler to
+ * detect when a hotplug event has occurred during the loading process.
+ * If 0, no detection occurs. Otherwise, the scheduler will fail to
+ * load if the sequence number does not match @scx_hotplug_seq on the
+ * enable path.
+ */
+ u64 hotplug_seq;
+
/**
* name - BPF scheduler's name
*
@@ -509,7 +563,9 @@ struct sched_ext_ops {
enum scx_opi {
SCX_OPI_BEGIN = 0,
SCX_OPI_NORMAL_BEGIN = 0,
- SCX_OPI_NORMAL_END = SCX_OP_IDX(init),
+ SCX_OPI_NORMAL_END = SCX_OP_IDX(cpu_online),
+ SCX_OPI_CPU_HOTPLUG_BEGIN = SCX_OP_IDX(cpu_online),
+ SCX_OPI_CPU_HOTPLUG_END = SCX_OP_IDX(init),
SCX_OPI_END = SCX_OP_IDX(init),
};
@@ -694,6 +750,7 @@ static atomic_t scx_exit_kind = ATOMIC_INIT(SCX_EXIT_DONE);
static struct scx_exit_info *scx_exit_info;
static atomic_long_t scx_nr_rejected = ATOMIC_LONG_INIT(0);
+static atomic_long_t scx_hotplug_seq = ATOMIC_LONG_INIT(0);
/*
* The maximum amount of time in jiffies that a task may be runnable without
@@ -1419,11 +1476,7 @@ static void direct_dispatch(struct task_struct *p, u64 enq_flags)
static bool scx_rq_online(struct rq *rq)
{
-#ifdef CONFIG_SMP
- return likely(rq->online);
-#else
- return true;
-#endif
+ return likely(rq->scx.flags & SCX_RQ_ONLINE);
}
static void do_enqueue_task(struct rq *rq, struct task_struct *p, u64 enq_flags,
@@ -1438,6 +1491,11 @@ static void do_enqueue_task(struct rq *rq, struct task_struct *p, u64 enq_flags,
if (sticky_cpu == cpu_of(rq))
goto local_norefill;
+ /*
+ * If !scx_rq_online(), we already told the BPF scheduler that the CPU
+ * is offline and are just running the hotplug path. Don't bother the
+ * BPF scheduler.
+ */
if (!scx_rq_online(rq))
goto local;
@@ -2673,6 +2731,42 @@ void __scx_update_idle(struct rq *rq, bool idle)
#endif
}
+static void handle_hotplug(struct rq *rq, bool online)
+{
+ int cpu = cpu_of(rq);
+
+ atomic_long_inc(&scx_hotplug_seq);
+
+ if (online && SCX_HAS_OP(cpu_online))
+ SCX_CALL_OP(SCX_KF_SLEEPABLE, cpu_online, cpu);
+ else if (!online && SCX_HAS_OP(cpu_offline))
+ SCX_CALL_OP(SCX_KF_SLEEPABLE, cpu_offline, cpu);
+ else
+ scx_ops_exit(SCX_ECODE_ACT_RESTART | SCX_ECODE_RSN_HOTPLUG,
+ "cpu %d going %s, exiting scheduler", cpu,
+ online ? "online" : "offline");
+}
+
+void scx_rq_activate(struct rq *rq)
+{
+ handle_hotplug(rq, true);
+}
+
+void scx_rq_deactivate(struct rq *rq)
+{
+ handle_hotplug(rq, false);
+}
+
+static void rq_online_scx(struct rq *rq)
+{
+ rq->scx.flags |= SCX_RQ_ONLINE;
+}
+
+static void rq_offline_scx(struct rq *rq)
+{
+ rq->scx.flags &= ~SCX_RQ_ONLINE;
+}
+
#else /* CONFIG_SMP */
static bool test_and_clear_cpu_idle(int cpu) { return false; }
@@ -3104,6 +3198,9 @@ DEFINE_SCHED_CLASS(ext) = {
.balance = balance_scx,
.select_task_rq = select_task_rq_scx,
.set_cpus_allowed = set_cpus_allowed_scx,
+
+ .rq_online = rq_online_scx,
+ .rq_offline = rq_offline_scx,
#endif
.task_tick = task_tick_scx,
@@ -3235,10 +3332,18 @@ static ssize_t scx_attr_nr_rejected_show(struct kobject *kobj,
}
SCX_ATTR(nr_rejected);
+static ssize_t scx_attr_hotplug_seq_show(struct kobject *kobj,
+ struct kobj_attribute *ka, char *buf)
+{
+ return sysfs_emit(buf, "%ld\n", atomic_long_read(&scx_hotplug_seq));
+}
+SCX_ATTR(hotplug_seq);
+
static struct attribute *scx_global_attrs[] = {
&scx_attr_state.attr,
&scx_attr_switch_all.attr,
&scx_attr_nr_rejected.attr,
+ &scx_attr_hotplug_seq.attr,
NULL,
};
@@ -3941,6 +4046,25 @@ static struct kthread_worker *scx_create_rt_helper(const char *name)
return helper;
}
+static void check_hotplug_seq(const struct sched_ext_ops *ops)
+{
+ unsigned long long global_hotplug_seq;
+
+ /*
+ * If a hotplug event has occurred between when a scheduler was
+ * initialized, and when we were able to attach, exit and notify user
+ * space about it.
+ */
+ if (ops->hotplug_seq) {
+ global_hotplug_seq = atomic_long_read(&scx_hotplug_seq);
+ if (ops->hotplug_seq != global_hotplug_seq) {
+ scx_ops_exit(SCX_ECODE_ACT_RESTART | SCX_ECODE_RSN_HOTPLUG,
+ "expected hotplug seq %llu did not match actual %llu",
+ ops->hotplug_seq, global_hotplug_seq);
+ }
+ }
+}
+
static int validate_ops(const struct sched_ext_ops *ops)
{
/*
@@ -4023,6 +4147,10 @@ static int scx_ops_enable(struct sched_ext_ops *ops, struct bpf_link *link)
}
}
+ for (i = SCX_OPI_CPU_HOTPLUG_BEGIN; i < SCX_OPI_CPU_HOTPLUG_END; i++)
+ if (((void (**)(void))ops)[i])
+ static_branch_enable_cpuslocked(&scx_has_op[i]);
+
cpus_read_unlock();
ret = validate_ops(ops);
@@ -4064,6 +4192,8 @@ static int scx_ops_enable(struct sched_ext_ops *ops, struct bpf_link *link)
percpu_down_write(&scx_fork_rwsem);
cpus_read_lock();
+ check_hotplug_seq(ops);
+
for (i = SCX_OPI_NORMAL_BEGIN; i < SCX_OPI_NORMAL_END; i++)
if (((void (**)(void))ops)[i])
static_branch_enable_cpuslocked(&scx_has_op[i]);
@@ -4374,6 +4504,9 @@ static int bpf_scx_init_member(const struct btf_type *t,
ops->exit_dump_len =
*(u32 *)(udata + moff) ?: SCX_EXIT_DUMP_DFL_LEN;
return 1;
+ case offsetof(struct sched_ext_ops, hotplug_seq):
+ ops->hotplug_seq = *(u64 *)(udata + moff);
+ return 1;
}
return 0;
@@ -4387,6 +4520,8 @@ static int bpf_scx_check_member(const struct btf_type *t,
switch (moff) {
case offsetof(struct sched_ext_ops, init_task):
+ case offsetof(struct sched_ext_ops, cpu_online):
+ case offsetof(struct sched_ext_ops, cpu_offline):
case offsetof(struct sched_ext_ops, init):
case offsetof(struct sched_ext_ops, exit):
break;
@@ -4457,6 +4592,8 @@ static s32 init_task_stub(struct task_struct *p, struct scx_init_task_args *args
static void exit_task_stub(struct task_struct *p, struct scx_exit_task_args *args) {}
static void enable_stub(struct task_struct *p) {}
static void disable_stub(struct task_struct *p) {}
+static void cpu_online_stub(s32 cpu) {}
+static void cpu_offline_stub(s32 cpu) {}
static s32 init_stub(void) { return -EINVAL; }
static void exit_stub(struct scx_exit_info *info) {}
@@ -4479,6 +4616,8 @@ static struct sched_ext_ops __bpf_ops_sched_ext_ops = {
.exit_task = exit_task_stub,
.enable = enable_stub,
.disable = disable_stub,
+ .cpu_online = cpu_online_stub,
+ .cpu_offline = cpu_offline_stub,
.init = init_stub,
.exit = exit_stub,
};
@@ -4719,6 +4858,9 @@ void __init init_sched_ext_class(void)
BUG_ON(!zalloc_cpumask_var(&rq->scx.cpus_to_preempt, GFP_KERNEL));
BUG_ON(!zalloc_cpumask_var(&rq->scx.cpus_to_wait, GFP_KERNEL));
init_irq_work(&rq->scx.kick_cpus_irq_work, kick_cpus_irq_workfn);
+
+ if (cpu_online(cpu))
+ cpu_rq(cpu)->scx.flags |= SCX_RQ_ONLINE;
}
register_sysrq_key('S', &sysrq_sched_ext_reset_op);
@@ -40,6 +40,8 @@ int scx_fork(struct task_struct *p);
void scx_post_fork(struct task_struct *p);
void scx_cancel_fork(struct task_struct *p);
bool scx_can_stop_tick(struct rq *rq);
+void scx_rq_activate(struct rq *rq);
+void scx_rq_deactivate(struct rq *rq);
int scx_check_setscheduler(struct task_struct *p, int policy);
bool task_should_scx(struct task_struct *p);
void init_sched_ext_class(void);
@@ -81,6 +83,8 @@ static inline int scx_fork(struct task_struct *p) { return 0; }
static inline void scx_post_fork(struct task_struct *p) {}
static inline void scx_cancel_fork(struct task_struct *p) {}
static inline bool scx_can_stop_tick(struct rq *rq) { return true; }
+static inline void scx_rq_activate(struct rq *rq) {}
+static inline void scx_rq_deactivate(struct rq *rq) {}
static inline int scx_check_setscheduler(struct task_struct *p, int policy) { return 0; }
static inline bool task_on_scx(const struct task_struct *p) { return false; }
static inline void init_sched_ext_class(void) {}
@@ -726,6 +726,12 @@ struct cfs_rq {
#ifdef CONFIG_SCHED_CLASS_EXT
/* scx_rq->flags, protected by the rq lock */
enum scx_rq_flags {
+ /*
+ * A hotplugged CPU starts scheduling before rq_online_scx(). Track
+ * ops.cpu_on/offline() state so that ops.enqueue/dispatch() are called
+ * only while the BPF scheduler considers the CPU to be online.
+ */
+ SCX_RQ_ONLINE = 1 << 0,
SCX_RQ_BALANCING = 1 << 1,
SCX_RQ_CAN_STOP_TICK = 1 << 2,
};
@@ -8,6 +8,9 @@
#define __SCX_COMPAT_H
#include <bpf/btf.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <unistd.h>
struct btf *__COMPAT_vmlinux_btf __attribute__((weak));
@@ -106,6 +109,28 @@ static inline bool __COMPAT_struct_has_field(const char *type, const char *field
#define SCX_OPS_SWITCH_PARTIAL \
__COMPAT_ENUM_OR_ZERO("scx_ops_flags", "SCX_OPS_SWITCH_PARTIAL")
+static inline long scx_hotplug_seq(void)
+{
+ int fd;
+ char buf[32];
+ ssize_t len;
+ long val;
+
+ fd = open("/sys/kernel/sched_ext/hotplug_seq", O_RDONLY);
+ if (fd < 0)
+ return -ENOENT;
+
+ len = read(fd, buf, sizeof(buf) - 1);
+ SCX_BUG_ON(len <= 0, "read failed (%ld)", len);
+ buf[len] = 0;
+ close(fd);
+
+ val = strtoul(buf, NULL, 10);
+ SCX_BUG_ON(val < 0, "invalid num hotplug events: %lu", val);
+
+ return val;
+}
+
/*
* struct sched_ext_ops can change over time. If compat.bpf.h::SCX_OPS_DEFINE()
* is used to define ops and compat.h::SCX_OPS_LOAD/ATTACH() are used to load
@@ -123,6 +148,7 @@ static inline bool __COMPAT_struct_has_field(const char *type, const char *field
\
__skel = __scx_name##__open(); \
SCX_BUG_ON(!__skel, "Could not open " #__scx_name); \
+ __skel->struct_ops.__ops_name->hotplug_seq = scx_hotplug_seq(); \
__skel; \
})
@@ -77,7 +77,35 @@ struct user_exit_info {
if (__uei->msg[0] != '\0') \
fprintf(stderr, " (%s)", __uei->msg); \
fputs("\n", stderr); \
+ __uei->exit_code; \
})
+/*
+ * We can't import vmlinux.h while compiling user C code. Let's duplicate
+ * scx_exit_code definition.
+ */
+enum scx_exit_code {
+ /* Reasons */
+ SCX_ECODE_RSN_HOTPLUG = 1LLU << 32,
+
+ /* Actions */
+ SCX_ECODE_ACT_RESTART = 1LLU << 48,
+};
+
+enum uei_ecode_mask {
+ UEI_ECODE_USER_MASK = ((1LLU << 32) - 1),
+ UEI_ECODE_SYS_RSN_MASK = ((1LLU << 16) - 1) << 32,
+ UEI_ECODE_SYS_ACT_MASK = ((1LLU << 16) - 1) << 48,
+};
+
+/*
+ * These macro interpret the ecode returned from UEI_REPORT().
+ */
+#define UEI_ECODE_USER(__ecode) ((__ecode) & UEI_ECODE_USER_MASK)
+#define UEI_ECODE_SYS_RSN(__ecode) ((__ecode) & UEI_ECODE_SYS_RSN_MASK)
+#define UEI_ECODE_SYS_ACT(__ecode) ((__ecode) & UEI_ECODE_SYS_ACT_MASK)
+
+#define UEI_ECODE_RESTART(__ecode) (UEI_ECODE_SYS_ACT((__ecode)) == SCX_ECODE_ACT_RESTART)
+
#endif /* __bpf__ */
#endif /* __USER_EXIT_INFO_H */
@@ -46,14 +46,14 @@ int main(int argc, char **argv)
{
struct scx_central *skel;
struct bpf_link *link;
- __u64 seq = 0;
+ __u64 seq = 0, ecode;
__s32 opt;
cpu_set_t *cpuset;
libbpf_set_print(libbpf_print_fn);
signal(SIGINT, sigint_handler);
signal(SIGTERM, sigint_handler);
-
+restart:
skel = SCX_OPS_OPEN(central_ops, scx_central);
skel->rodata->central_cpu = 0;
@@ -126,7 +126,10 @@ int main(int argc, char **argv)
}
bpf_link__destroy(link);
- UEI_REPORT(skel, uei);
+ ecode = UEI_REPORT(skel, uei);
scx_central__destroy(skel);
+
+ if (UEI_ECODE_RESTART(ecode))
+ goto restart;
return 0;
}
@@ -358,8 +358,63 @@ void BPF_STRUCT_OPS(qmap_dump_task, struct scx_dump_ctx *dctx, struct task_struc
taskc->force_local);
}
+/*
+ * 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)
+{
+ 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)
+{
+ bpf_printk("CPU %d going offline", cpu);
+ /* @cpu is still online at this point */
+ print_cpus();
+}
+
s32 BPF_STRUCT_OPS_SLEEPABLE(qmap_init)
{
+ print_cpus();
+
return scx_bpf_create_dsq(SHARED_DSQ, -1);
}
@@ -378,6 +433,8 @@ SCX_OPS_DEFINE(qmap_ops,
.dump = (void *)qmap_dump,
.dump_cpu = (void *)qmap_dump_cpu,
.dump_task = (void *)qmap_dump_task,
+ .cpu_online = (void *)qmap_cpu_online,
+ .cpu_offline = (void *)qmap_cpu_offline,
.init = (void *)qmap_init,
.exit = (void *)qmap_exit,
.timeout_ms = 5000U,
@@ -122,5 +122,9 @@ int main(int argc, char **argv)
bpf_link__destroy(link);
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.
+ */
return 0;
}
@@ -62,11 +62,12 @@ int main(int argc, char **argv)
struct scx_simple *skel;
struct bpf_link *link;
__u32 opt;
+ __u64 ecode;
libbpf_set_print(libbpf_print_fn);
signal(SIGINT, sigint_handler);
signal(SIGTERM, sigint_handler);
-
+restart:
skel = SCX_OPS_OPEN(simple_ops, scx_simple);
while ((opt = getopt(argc, argv, "vh")) != -1) {
@@ -93,7 +94,10 @@ int main(int argc, char **argv)
}
bpf_link__destroy(link);
- UEI_REPORT(skel, uei);
+ ecode = UEI_REPORT(skel, uei);
scx_simple__destroy(skel);
+
+ if (UEI_ECODE_RESTART(ecode))
+ goto restart;
return 0;
}
Add ops.cpu_online/offline() which are invoked when CPUs come online and offline respectively. As the enqueue path already automatically bypasses tasks to the local dsq on a deactivated CPU, BPF schedulers are guaranteed to see tasks only on CPUs which are between online() and offline(). If the BPF scheduler doesn't implement ops.cpu_online/offline(), the scheduler is automatically exited with SCX_ECODE_RESTART | SCX_ECODE_RSN_HOTPLUG. Userspace can implement CPU hotpplug support trivially by simply reinitializing and reloading the scheduler. scx_qmap is updated to print out online CPUs on hotplug events. Other schedulers are updated to restart based on ecode. v3: - The previous implementation added @reason to sched_class.rq_on/offline() to distinguish between CPU hotplug events and topology updates. This was buggy and fragile as the methods are skipped if the current state equals the target state. Instead, add scx_rq_[de]activate() which are directly called from sched_cpu_de/activate(). This also allows ops.cpu_on/offline() to sleep which can be useful. - ops.dispatch() could be called on a CPU that the BPF scheduler was told to be offline. The dispatch patch is updated to bypass in such cases. v2: - To accommodate lock ordering change between scx_cgroup_rwsem and cpus_read_lock(), CPU hotplug operations are put into its own SCX_OPI block and enabled eariler during scx_ope_enable() so that cpus_read_lock() can be dropped before acquiring scx_cgroup_rwsem. - Auto exit with ECODE added. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: David Vernet <dvernet@meta.com> Acked-by: Josh Don <joshdon@google.com> Acked-by: Hao Luo <haoluo@google.com> Acked-by: Barret Rhoden <brho@google.com> --- kernel/sched/core.c | 4 + kernel/sched/ext.c | 156 ++++++++++++++++++- kernel/sched/ext.h | 4 + kernel/sched/sched.h | 6 + tools/sched_ext/include/scx/compat.h | 26 ++++ tools/sched_ext/include/scx/user_exit_info.h | 28 ++++ tools/sched_ext/scx_central.c | 9 +- tools/sched_ext/scx_qmap.bpf.c | 57 +++++++ tools/sched_ext/scx_qmap.c | 4 + tools/sched_ext/scx_simple.c | 8 +- 10 files changed, 290 insertions(+), 12 deletions(-)