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Message-Id: <20230128001639.3510083-19-tj@kernel.org> Date: Fri, 27 Jan 2023 14:16:27 -1000 From: Tejun Heo <tj@...nel.org> To: torvalds@...ux-foundation.org, mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com, vincent.guittot@...aro.org, dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com, ast@...nel.org, daniel@...earbox.net, andrii@...nel.org, martin.lau@...nel.org, joshdon@...gle.com, brho@...gle.com, pjt@...gle.com, derkling@...gle.com, haoluo@...gle.com, dvernet@...a.com, dschatzberg@...a.com, dskarlat@...cmu.edu, riel@...riel.com Cc: linux-kernel@...r.kernel.org, bpf@...r.kernel.org, kernel-team@...a.com, Tejun Heo <tj@...nel.org> Subject: [PATCH 18/30] sched_ext: Allow BPF schedulers to switch all eligible tasks into sched_ext Currently, to use sched_ext, each task has to be put into sched_ext using sched_setscheduler(2). However, some BPF schedulers and use cases might prefer to service all eligible tasks. This patch adds a new kfunc helper, scx_bpf_switch_all(), that BPF schedulers can call from ops.init() to switch all SCHED_NORMAL, SCHED_BATCH and SCHED_IDLE tasks into sched_ext. This has the benefit that the scheduler swaps are transparent to the users and applications. As we know that CFS is not being used when scx_bpf_switch_all() is used, we can also disable hot path entry points with static_branches. Both the dummy and qmap example schedulers are updated with the '-a' option which enables the switch_all behavior. Signed-off-by: Tejun Heo <tj@...nel.org> Suggested-by: Barret Rhoden <brho@...gle.com> Reviewed-by: David Vernet <dvernet@...a.com> Acked-by: Josh Don <joshdon@...gle.com> Acked-by: Hao Luo <haoluo@...gle.com> Acked-by: Barret Rhoden <brho@...gle.com> --- kernel/sched/core.c | 8 +++-- kernel/sched/ext.c | 45 +++++++++++++++++++++++++ kernel/sched/ext.h | 5 +++ tools/sched_ext/scx_common.bpf.h | 1 + tools/sched_ext/scx_example_dummy.bpf.c | 11 ++++++ tools/sched_ext/scx_example_dummy.c | 8 +++-- tools/sched_ext/scx_example_qmap.bpf.c | 9 +++++ tools/sched_ext/scx_example_qmap.c | 7 ++-- 8 files changed, 87 insertions(+), 7 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 9e566e72c3f2..5b68b822312b 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1204,7 +1204,7 @@ bool sched_can_stop_tick(struct rq *rq) * if there's more than one we need the tick for involuntary * preemption. */ - if (rq->nr_running > 1) + if (!scx_switched_all() && rq->nr_running > 1) return false; return true; @@ -5590,8 +5590,10 @@ void scheduler_tick(void) perf_event_task_tick(); #ifdef CONFIG_SMP - rq->idle_balance = idle_cpu(cpu); - trigger_load_balance(rq); + if (!scx_switched_all()) { + rq->idle_balance = idle_cpu(cpu); + trigger_load_balance(rq); + } #endif } diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index b9d55c25cec9..63f0a3cf2d53 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -73,6 +73,10 @@ static DEFINE_MUTEX(scx_ops_enable_mutex); DEFINE_STATIC_KEY_FALSE(__scx_ops_enabled); DEFINE_STATIC_PERCPU_RWSEM(scx_fork_rwsem); static atomic_t scx_ops_enable_state_var = ATOMIC_INIT(SCX_OPS_DISABLED); +static bool scx_switch_all_req; +static bool scx_switching_all; +DEFINE_STATIC_KEY_FALSE(__scx_switched_all); + static struct sched_ext_ops scx_ops; static bool scx_warned_zero_slice; @@ -1966,6 +1970,8 @@ bool task_on_scx(struct task_struct *p) { if (!scx_enabled() || scx_ops_disabling()) return false; + if (READ_ONCE(scx_switching_all)) + return true; return p->policy == SCHED_EXT; } @@ -2092,6 +2098,9 @@ static void scx_ops_disable_workfn(struct kthread_work *work) */ mutex_lock(&scx_ops_enable_mutex); + static_branch_disable(&__scx_switched_all); + WRITE_ONCE(scx_switching_all, false); + /* avoid racing against fork */ cpus_read_lock(); percpu_down_write(&scx_fork_rwsem); @@ -2276,6 +2285,7 @@ static int scx_ops_enable(struct sched_ext_ops *ops) */ cpus_read_lock(); + scx_switch_all_req = false; if (scx_ops.init) { ret = SCX_CALL_OP_RET(SCX_KF_INIT | SCX_KF_SLEEPABLE, init); if (ret) { @@ -2391,6 +2401,8 @@ static int scx_ops_enable(struct sched_ext_ops *ops) * transitions here are synchronized against sched_ext_free() through * scx_tasks_lock. */ + WRITE_ONCE(scx_switching_all, scx_switch_all_req); + scx_task_iter_init(&sti); while ((p = scx_task_iter_next_filtered_locked(&sti))) { if (READ_ONCE(p->__state) != TASK_DEAD) { @@ -2422,6 +2434,9 @@ static int scx_ops_enable(struct sched_ext_ops *ops) goto err_disable_unlock; } + if (scx_switch_all_req) + static_branch_enable_cpuslocked(&__scx_switched_all); + cpus_read_unlock(); mutex_unlock(&scx_ops_enable_mutex); @@ -2456,6 +2471,9 @@ static int scx_debug_show(struct seq_file *m, void *v) mutex_lock(&scx_ops_enable_mutex); seq_printf(m, "%-30s: %s\n", "ops", scx_ops.name); seq_printf(m, "%-30s: %ld\n", "enabled", scx_enabled()); + seq_printf(m, "%-30s: %d\n", "switching_all", + READ_ONCE(scx_switching_all)); + seq_printf(m, "%-30s: %ld\n", "switched_all", scx_switched_all()); seq_printf(m, "%-30s: %s\n", "enable_state", scx_ops_enable_state_str[scx_ops_enable_state()]); seq_printf(m, "%-30s: %llu\n", "nr_rejected", @@ -2694,6 +2712,31 @@ __diag_push(); __diag_ignore_all("-Wmissing-prototypes", "Global functions as their definitions will be in vmlinux BTF"); +/** + * scx_bpf_switch_all - Switch all tasks into SCX + * @into_scx: switch direction + * + * If @into_scx is %true, all existing and future non-dl/rt tasks are switched + * to SCX. If %false, only tasks which have %SCHED_EXT explicitly set are put on + * SCX. The actual switching is asynchronous. Can be called from ops.init(). + */ +void scx_bpf_switch_all(void) +{ + if (!scx_kf_allowed(SCX_KF_INIT)) + return; + + scx_switch_all_req = true; +} + +BTF_SET8_START(scx_kfunc_ids_init) +BTF_ID_FLAGS(func, scx_bpf_switch_all) +BTF_SET8_END(scx_kfunc_ids_init) + +static const struct btf_kfunc_id_set scx_kfunc_set_init = { + .owner = THIS_MODULE, + .set = &scx_kfunc_ids_init, +}; + /** * scx_bpf_create_dsq - Create a custom DSQ * @dsq_id: DSQ to create @@ -3131,6 +3174,8 @@ static int __init register_ext_kfuncs(void) * check using scx_kf_allowed(). */ if ((ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, + &scx_kfunc_set_init)) || + (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &scx_kfunc_set_sleepable)) || (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &scx_kfunc_set_enqueue_dispatch)) || diff --git a/kernel/sched/ext.h b/kernel/sched/ext.h index 76c94babd19e..a4fe649e649d 100644 --- a/kernel/sched/ext.h +++ b/kernel/sched/ext.h @@ -60,7 +60,9 @@ extern unsigned long scx_watchdog_timeout; extern unsigned long scx_watchdog_timestamp; DECLARE_STATIC_KEY_FALSE(__scx_ops_enabled); +DECLARE_STATIC_KEY_FALSE(__scx_switched_all); #define scx_enabled() static_branch_unlikely(&__scx_ops_enabled) +#define scx_switched_all() static_branch_unlikely(&__scx_switched_all) bool task_on_scx(struct task_struct *p); void scx_pre_fork(struct task_struct *p); @@ -95,6 +97,8 @@ static inline void scx_notify_sched_tick(void) static inline const struct sched_class *next_active_class(const struct sched_class *class) { class++; + if (scx_switched_all() && class == &fair_sched_class) + class++; if (!scx_enabled() && class == &ext_sched_class) class++; return class; @@ -117,6 +121,7 @@ static inline const struct sched_class *next_active_class(const struct sched_cla #else /* CONFIG_SCHED_CLASS_EXT */ #define scx_enabled() false +#define scx_switched_all() false static inline void scx_pre_fork(struct task_struct *p) {} static inline int scx_fork(struct task_struct *p) { return 0; } diff --git a/tools/sched_ext/scx_common.bpf.h b/tools/sched_ext/scx_common.bpf.h index b40a4fc6a159..fec19e8d0681 100644 --- a/tools/sched_ext/scx_common.bpf.h +++ b/tools/sched_ext/scx_common.bpf.h @@ -66,6 +66,7 @@ bool bpf_cpumask_and(struct bpf_cpumask *dst, const struct cpumask *src1, const struct cpumask *src2) __ksym; u32 bpf_cpumask_first(const struct cpumask *cpumask) __ksym; +void scx_bpf_switch_all(void) __ksym; s32 scx_bpf_create_dsq(u64 dsq_id, s32 node) __ksym; bool scx_bpf_consume(u64 dsq_id) __ksym; u32 scx_bpf_dispatch_nr_slots(void) __ksym; diff --git a/tools/sched_ext/scx_example_dummy.bpf.c b/tools/sched_ext/scx_example_dummy.bpf.c index ac7b490b5a39..28251373d1c3 100644 --- a/tools/sched_ext/scx_example_dummy.bpf.c +++ b/tools/sched_ext/scx_example_dummy.bpf.c @@ -7,6 +7,7 @@ * * - Statistics tracking how many are queued to local and global dsq's. * - Termination notification for userspace. + * - Support for switch_all. * * Copyright (c) 2022 Meta Platforms, Inc. and affiliates. * Copyright (c) 2022 Tejun Heo <tj@...nel.org> @@ -16,6 +17,8 @@ char _license[] SEC("license") = "GPL"; +const volatile bool switch_all; + struct user_exit_info uei; struct { @@ -32,6 +35,13 @@ static void stat_inc(u32 idx) (*cnt_p)++; } +s32 BPF_STRUCT_OPS(dummy_init) +{ + if (switch_all) + scx_bpf_switch_all(); + return 0; +} + void BPF_STRUCT_OPS(dummy_enqueue, struct task_struct *p, u64 enq_flags) { if (enq_flags & SCX_ENQ_LOCAL) { @@ -51,6 +61,7 @@ void BPF_STRUCT_OPS(dummy_exit, struct scx_exit_info *ei) SEC(".struct_ops") struct sched_ext_ops dummy_ops = { .enqueue = (void *)dummy_enqueue, + .init = (void *)dummy_init, .exit = (void *)dummy_exit, .name = "dummy", }; diff --git a/tools/sched_ext/scx_example_dummy.c b/tools/sched_ext/scx_example_dummy.c index 72881c881830..9229973e8698 100644 --- a/tools/sched_ext/scx_example_dummy.c +++ b/tools/sched_ext/scx_example_dummy.c @@ -19,8 +19,9 @@ const char help_fmt[] = "\n" "See the top-level comment in .bpf.c for more details.\n" "\n" -"Usage: %s\n" +"Usage: %s [-a]\n" "\n" +" -a Switch all tasks\n" " -h Display this help and exit\n"; static volatile int exit_req; @@ -64,8 +65,11 @@ int main(int argc, char **argv) skel = scx_example_dummy__open(); assert(skel); - while ((opt = getopt(argc, argv, "h")) != -1) { + while ((opt = getopt(argc, argv, "ah")) != -1) { switch (opt) { + case 'a': + skel->rodata->switch_all = true; + break; default: fprintf(stderr, help_fmt, basename(argv[0])); return opt != 'h'; diff --git a/tools/sched_ext/scx_example_qmap.bpf.c b/tools/sched_ext/scx_example_qmap.bpf.c index 46bc16ed301f..ec8c4ee7ef16 100644 --- a/tools/sched_ext/scx_example_qmap.bpf.c +++ b/tools/sched_ext/scx_example_qmap.bpf.c @@ -22,6 +22,7 @@ char _license[] SEC("license") = "GPL"; const volatile u64 slice_ns = SCX_SLICE_DFL; +const volatile bool switch_all; const volatile u32 stall_user_nth; const volatile u32 stall_kernel_nth; const volatile s32 disallow_tgid; @@ -236,6 +237,13 @@ s32 BPF_STRUCT_OPS(qmap_prep_enable, struct task_struct *p, return -ENOMEM; } +s32 BPF_STRUCT_OPS(qmap_init) +{ + if (switch_all) + scx_bpf_switch_all(); + return 0; +} + void BPF_STRUCT_OPS(qmap_exit, struct scx_exit_info *ei) { uei_record(&uei, ei); @@ -248,6 +256,7 @@ struct sched_ext_ops qmap_ops = { .dequeue = (void *)qmap_dequeue, .dispatch = (void *)qmap_dispatch, .prep_enable = (void *)qmap_prep_enable, + .init = (void *)qmap_init, .exit = (void *)qmap_exit, .timeout_ms = 5000U, .name = "qmap", diff --git a/tools/sched_ext/scx_example_qmap.c b/tools/sched_ext/scx_example_qmap.c index dff9323dfd20..30633122e6d5 100644 --- a/tools/sched_ext/scx_example_qmap.c +++ b/tools/sched_ext/scx_example_qmap.c @@ -20,7 +20,7 @@ const char help_fmt[] = "\n" "See the top-level comment in .bpf.c for more details.\n" "\n" -"Usage: %s [-s SLICE_US] [-e COUNT] [-t COUNT] [-T COUNT] [-d PID]\n" +"Usage: %s [-a] [-s SLICE_US] [-e COUNT] [-t COUNT] [-T COUNT] [-d PID]\n" "\n" " -s SLICE_US Override slice duration\n" " -e COUNT Trigger scx_bpf_error() after COUNT enqueues\n" @@ -50,8 +50,11 @@ int main(int argc, char **argv) skel = scx_example_qmap__open(); assert(skel); - while ((opt = getopt(argc, argv, "hs:e:t:T:d:")) != -1) { + while ((opt = getopt(argc, argv, "ahs:e:t:T:d:")) != -1) { switch (opt) { + case 'a': + skel->rodata->switch_all = true; + break; case 's': skel->rodata->slice_ns = strtoull(optarg, NULL, 0) * 1000; break; -- 2.39.1
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