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[2603:800c:1a02:1bae:a7fa:157f:969a:4cde]) by smtp.gmail.com with ESMTPSA id z5-20020a6552c5000000b0050301521335sm1879410pgp.11.2023.03.17.14.34.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 17 Mar 2023 14:34:15 -0700 (PDT) Sender: Tejun Heo From: Tejun Heo To: torvalds@linux-foundation.org, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@kernel.org, joshdon@google.com, brho@google.com, pjt@google.com, derkling@google.com, haoluo@google.com, dvernet@meta.com, dschatzberg@meta.com, dskarlat@cs.cmu.edu, riel@surriel.com Cc: linux-kernel@vger.kernel.org, bpf@vger.kernel.org, kernel-team@meta.com, Tejun Heo Subject: [PATCH 18/32] sched_ext: Allow BPF schedulers to switch all eligible tasks into sched_ext Date: Fri, 17 Mar 2023 11:33:19 -1000 Message-Id: <20230317213333.2174969-19-tj@kernel.org> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230317213333.2174969-1-tj@kernel.org> References: <20230317213333.2174969-1-tj@kernel.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org 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 simple and qmap example schedulers are updated to switch all tasks by default to ease testing. '-p' option is added which enables the original behavior of switching only tasks which are explicitly on SCHED_EXT. v2: In the example schedulers, switch all tasks by default. Signed-off-by: Tejun Heo Suggested-by: Barret Rhoden Reviewed-by: David Vernet Acked-by: Josh Don Acked-by: Hao Luo Acked-by: Barret Rhoden --- 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_qmap.bpf.c | 9 +++++ tools/sched_ext/scx_example_qmap.c | 8 +++-- tools/sched_ext/scx_example_simple.bpf.c | 10 ++++++ tools/sched_ext/scx_example_simple.c | 8 +++-- 8 files changed, 87 insertions(+), 7 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 08a72f146f9d..bc90327f950d 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1206,7 +1206,7 @@ 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; @@ -5657,8 +5657,10 @@ 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 52744d7dd181..ed2f13d90fcb 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; @@ -2015,6 +2019,8 @@ 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; } @@ -2141,6 +2147,9 @@ 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); @@ -2325,6 +2334,7 @@ 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, init); if (ret) { @@ -2440,6 +2450,8 @@ 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) { @@ -2471,6 +2483,9 @@ 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); @@ -2505,6 +2520,9 @@ 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", @@ -2743,6 +2761,31 @@ __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 @@ -3194,6 +3237,8 @@ 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 69fd41a55a3c..5efb58e1eb6a 100644 --- a/tools/sched_ext/scx_common.bpf.h +++ b/tools/sched_ext/scx_common.bpf.h @@ -52,6 +52,7 @@ void ___scx_bpf_error_format_checker(const char *fmt, ...) {} ___scx_bpf_error_format_checker(fmt, ##args); \ }) +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_qmap.bpf.c b/tools/sched_ext/scx_example_qmap.bpf.c index 0e4cccf878f5..abb134fb18ce 100644 --- a/tools/sched_ext/scx_example_qmap.bpf.c +++ b/tools/sched_ext/scx_example_qmap.bpf.c @@ -25,6 +25,7 @@ char _license[] SEC("license") = "GPL"; const volatile u64 slice_ns = SCX_SLICE_DFL; +const volatile bool switch_partial; const volatile u32 stall_user_nth; const volatile u32 stall_kernel_nth; const volatile s32 disallow_tgid; @@ -239,6 +240,13 @@ s32 BPF_STRUCT_OPS(qmap_prep_enable, struct task_struct *p, return -ENOMEM; } +s32 BPF_STRUCT_OPS(qmap_init) +{ + if (!switch_partial) + scx_bpf_switch_all(); + return 0; +} + void BPF_STRUCT_OPS(qmap_exit, struct scx_exit_info *ei) { uei_record(&uei, ei); @@ -251,6 +259,7 @@ 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 d080a0c853c0..f94fd39c4ed8 100644 --- a/tools/sched_ext/scx_example_qmap.c +++ b/tools/sched_ext/scx_example_qmap.c @@ -20,13 +20,14 @@ 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 [-s SLICE_US] [-e COUNT] [-t COUNT] [-T COUNT] [-d PID] [-p]\n" "\n" " -s SLICE_US Override slice duration\n" " -e COUNT Trigger scx_bpf_error() after COUNT enqueues\n" " -t COUNT Stall every COUNT'th user thread\n" " -T COUNT Stall every COUNT'th kernel thread\n" " -d PID Disallow a process from switching into SCHED_EXT (-1 for self)\n" +" -p Switch only tasks on SCHED_EXT policy intead of all\n" " -h Display this help and exit\n"; static volatile int exit_req; @@ -50,7 +51,7 @@ int main(int argc, char **argv) skel = scx_example_qmap__open(); assert(skel); - while ((opt = getopt(argc, argv, "s:e:t:T:d:h")) != -1) { + while ((opt = getopt(argc, argv, "s:e:t:T:d:ph")) != -1) { switch (opt) { case 's': skel->rodata->slice_ns = strtoull(optarg, NULL, 0) * 1000; @@ -69,6 +70,9 @@ int main(int argc, char **argv) if (skel->rodata->disallow_tgid < 0) skel->rodata->disallow_tgid = getpid(); break; + case 'p': + skel->rodata->switch_partial = true; + break; default: fprintf(stderr, help_fmt, basename(argv[0])); return opt != 'h'; diff --git a/tools/sched_ext/scx_example_simple.bpf.c b/tools/sched_ext/scx_example_simple.bpf.c index 74716d0dd08d..fa5ae683ace1 100644 --- a/tools/sched_ext/scx_example_simple.bpf.c +++ b/tools/sched_ext/scx_example_simple.bpf.c @@ -15,6 +15,8 @@ char _license[] SEC("license") = "GPL"; +const volatile bool switch_partial; + struct user_exit_info uei; struct { @@ -43,6 +45,13 @@ void BPF_STRUCT_OPS(simple_enqueue, struct task_struct *p, u64 enq_flags) scx_bpf_dispatch(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL, enq_flags); } +s32 BPF_STRUCT_OPS(simple_init) +{ + if (!switch_partial) + scx_bpf_switch_all(); + return 0; +} + void BPF_STRUCT_OPS(simple_exit, struct scx_exit_info *ei) { uei_record(&uei, ei); @@ -51,6 +60,7 @@ void BPF_STRUCT_OPS(simple_exit, struct scx_exit_info *ei) SEC(".struct_ops") struct sched_ext_ops simple_ops = { .enqueue = (void *)simple_enqueue, + .init = (void *)simple_init, .exit = (void *)simple_exit, .name = "simple", }; diff --git a/tools/sched_ext/scx_example_simple.c b/tools/sched_ext/scx_example_simple.c index 2f1ee40f7e5a..868fd39e45c7 100644 --- a/tools/sched_ext/scx_example_simple.c +++ b/tools/sched_ext/scx_example_simple.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 [-p]\n" "\n" +" -p Switch only tasks on SCHED_EXT policy intead of all\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_simple__open(); assert(skel); - while ((opt = getopt(argc, argv, "h")) != -1) { + while ((opt = getopt(argc, argv, "ph")) != -1) { switch (opt) { + case 'p': + skel->rodata->switch_partial = true; + break; default: fprintf(stderr, help_fmt, basename(argv[0])); return opt != 'h';