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[2603:800c:1a02:1bae:a7fa:157f:969a:4cde]) by smtp.gmail.com with ESMTPSA id 6-20020a170902c20600b0019b089bc8d7sm1997428pll.78.2023.03.17.14.34.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 17 Mar 2023 14:34:28 -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 25/32] sched_ext: Implement SCX_KICK_WAIT Date: Fri, 17 Mar 2023 11:33:26 -1000 Message-Id: <20230317213333.2174969-26-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 From: David Vernet If set when calling scx_bpf_kick_cpu(), the invoking CPU will busy wait for the kicked cpu to enter the scheduler. This will be used to improve the exclusion guarantees in scx_example_pair. Signed-off-by: David Vernet Reviewed-by: Tejun Heo Signed-off-by: Tejun Heo Acked-by: Josh Don Acked-by: Hao Luo Acked-by: Barret Rhoden --- kernel/sched/core.c | 4 +++- kernel/sched/ext.c | 33 ++++++++++++++++++++++++++++++++- kernel/sched/ext.h | 20 ++++++++++++++++++++ kernel/sched/sched.h | 2 ++ 4 files changed, 57 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 0780414f3c15..ff51977968fb 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6019,8 +6019,10 @@ __pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) for_each_active_class(class) { p = class->pick_next_task(rq); - if (p) + if (p) { + scx_notify_pick_next_task(rq, p, class); return p; + } } BUG(); /* The idle class should always have a runnable task. */ diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index 736f764d0f62..fbdbe4603853 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -126,6 +126,9 @@ static struct { static bool __cacheline_aligned_in_smp scx_has_idle_cpus; #endif /* CONFIG_SMP */ +/* for %SCX_KICK_WAIT */ +static u64 __percpu *scx_kick_cpus_pnt_seqs; + /* * Direct dispatch marker. * @@ -3215,6 +3218,7 @@ static const struct sysrq_key_op sysrq_sched_ext_reset_op = { static void kick_cpus_irq_workfn(struct irq_work *irq_work) { struct rq *this_rq = this_rq(); + u64 *pseqs = this_cpu_ptr(scx_kick_cpus_pnt_seqs); int this_cpu = cpu_of(this_rq); int cpu; @@ -3228,14 +3232,32 @@ static void kick_cpus_irq_workfn(struct irq_work *irq_work) if (cpumask_test_cpu(cpu, this_rq->scx.cpus_to_preempt) && rq->curr->sched_class == &ext_sched_class) rq->curr->scx.slice = 0; + pseqs[cpu] = rq->scx.pnt_seq; resched_curr(rq); + } else { + cpumask_clear_cpu(cpu, this_rq->scx.cpus_to_wait); } raw_spin_rq_unlock_irqrestore(rq, flags); } + for_each_cpu_andnot(cpu, this_rq->scx.cpus_to_wait, + cpumask_of(this_cpu)) { + /* + * Pairs with smp_store_release() issued by this CPU in + * scx_notify_pick_next_task() on the resched path. + * + * We busy-wait here to guarantee that no other task can be + * scheduled on our core before the target CPU has entered the + * resched path. + */ + while (smp_load_acquire(&cpu_rq(cpu)->scx.pnt_seq) == pseqs[cpu]) + cpu_relax(); + } + cpumask_clear(this_rq->scx.cpus_to_kick); cpumask_clear(this_rq->scx.cpus_to_preempt); + cpumask_clear(this_rq->scx.cpus_to_wait); } void __init init_sched_ext_class(void) @@ -3249,7 +3271,7 @@ void __init init_sched_ext_class(void) * through the generated vmlinux.h. */ WRITE_ONCE(v, SCX_WAKE_EXEC | SCX_ENQ_WAKEUP | SCX_DEQ_SLEEP | - SCX_TG_ONLINE); + SCX_TG_ONLINE | SCX_KICK_PREEMPT); BUG_ON(rhashtable_init(&dsq_hash, &dsq_hash_params)); init_dsq(&scx_dsq_global, SCX_DSQ_GLOBAL); @@ -3257,6 +3279,12 @@ void __init init_sched_ext_class(void) BUG_ON(!alloc_cpumask_var(&idle_masks.cpu, GFP_KERNEL)); BUG_ON(!alloc_cpumask_var(&idle_masks.smt, GFP_KERNEL)); #endif + scx_kick_cpus_pnt_seqs = + __alloc_percpu(sizeof(scx_kick_cpus_pnt_seqs[0]) * + num_possible_cpus(), + __alignof__(scx_kick_cpus_pnt_seqs[0])); + BUG_ON(!scx_kick_cpus_pnt_seqs); + for_each_possible_cpu(cpu) { struct rq *rq = cpu_rq(cpu); @@ -3265,6 +3293,7 @@ void __init init_sched_ext_class(void) BUG_ON(!zalloc_cpumask_var(&rq->scx.cpus_to_kick, GFP_KERNEL)); 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); } @@ -3533,6 +3562,8 @@ void scx_bpf_kick_cpu(s32 cpu, u64 flags) cpumask_set_cpu(cpu, rq->scx.cpus_to_kick); if (flags & SCX_KICK_PREEMPT) cpumask_set_cpu(cpu, rq->scx.cpus_to_preempt); + if (flags & SCX_KICK_WAIT) + cpumask_set_cpu(cpu, rq->scx.cpus_to_wait); irq_work_queue(&rq->scx.kick_cpus_irq_work); preempt_enable(); diff --git a/kernel/sched/ext.h b/kernel/sched/ext.h index 0c5a109e7e6d..fc27b28acfde 100644 --- a/kernel/sched/ext.h +++ b/kernel/sched/ext.h @@ -66,6 +66,7 @@ enum scx_tg_flags { enum scx_kick_flags { SCX_KICK_PREEMPT = 1LLU << 0, /* force scheduling on the CPU */ + SCX_KICK_WAIT = 1LLU << 1, /* wait for the CPU to be rescheduled */ }; #ifdef CONFIG_SCHED_CLASS_EXT @@ -95,6 +96,22 @@ __printf(2, 3) void scx_ops_error_type(enum scx_exit_type type, #define scx_ops_error(fmt, args...) \ scx_ops_error_type(SCX_EXIT_ERROR, fmt, ##args) +static inline void scx_notify_pick_next_task(struct rq *rq, + const struct task_struct *p, + const struct sched_class *active) +{ +#ifdef CONFIG_SMP + if (!scx_enabled()) + return; + /* + * Pairs with the smp_load_acquire() issued by a CPU in + * kick_cpus_irq_workfn() who is waiting for this CPU to perform a + * resched. + */ + smp_store_release(&rq->scx.pnt_seq, rq->scx.pnt_seq + 1); +#endif +} + static inline void scx_notify_sched_tick(void) { unsigned long last_check; @@ -149,6 +166,9 @@ static inline int scx_check_setscheduler(struct task_struct *p, int policy) { return 0; } static inline bool scx_can_stop_tick(struct rq *rq) { return true; } static inline void init_sched_ext_class(void) {} +static inline void scx_notify_pick_next_task(struct rq *rq, + const struct task_struct *p, + const struct sched_class *active) {} static inline void scx_notify_sched_tick(void) {} #define for_each_active_class for_each_class diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 3571cfda62a3..4b7f48239248 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -710,6 +710,8 @@ struct scx_rq { u32 flags; cpumask_var_t cpus_to_kick; cpumask_var_t cpus_to_preempt; + cpumask_var_t cpus_to_wait; + u64 pnt_seq; struct irq_work kick_cpus_irq_work; }; #endif /* CONFIG_SCHED_CLASS_EXT */