From patchwork Sat Nov 11 02:47:54 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tejun Heo X-Patchwork-Id: 13452945 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 557B41860 for ; Sat, 11 Nov 2023 02:52:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="ZtK6JhxG" Received: from mail-oo1-xc2f.google.com (mail-oo1-xc2f.google.com [IPv6:2607:f8b0:4864:20::c2f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A52C25583; Fri, 10 Nov 2023 18:49:51 -0800 (PST) Received: by mail-oo1-xc2f.google.com with SMTP id 006d021491bc7-58441865ffaso1509379eaf.1; Fri, 10 Nov 2023 18:49:51 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1699670991; x=1700275791; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:sender:from:to:cc:subject:date :message-id:reply-to; bh=CZeI9725myAVZqLqZVa1czCaq5DHZFEpHH3TfTd4WoI=; b=ZtK6JhxGTIcsu7awOLLGDg77MejbNd/tfpfGwHKBZ1VhvShdiq2UVav1O/EXreA8iw umcsj67I/Xj+NcbcPYXigKusEPYz8is/t1ge0RnF/5oiOn9AHtWq6XdgvoLGbLn+1Ntg cOJ7vXh/eA4lbgkVztEvpeTJC2B9XJne2ffJF3UZlk9LDHr4dG5ABNQYXOz3h0aXs2/k GyNC6cQz10IMcWqO7iPz/rl9B+8EtMaqeXZyUrhN8gyNEgxrYt7gnnuRqnmIgAtCrF1m d72wfKBwaScFR57CpY77UmHQhms+nleDkNEOurwdtWv2m5RjlaSrTUEs7bzaIdyB+kdx KuOw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1699670991; x=1700275791; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:sender:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=CZeI9725myAVZqLqZVa1czCaq5DHZFEpHH3TfTd4WoI=; b=BMdLF0tAF7brzd0Px9chTdTEvEsZ7aDyu7+slW6w3KdsRYhjtxCHnFzefGhOag10V8 hLBvJ50tHGSQYUTa+SX4a4EIGY9OhS7xON3Kp1aW2IQ27jg7fsxxl7QXuRvWSt0Q+V+X fi+zk/DTQGUBsLCiA071J2YZvwgH3qidZDYrsGPv/X2t/1cHJJdUjH3qVivF2cO7rbb7 V7Pd+ZmJElRp/ReJDDRggS2Mv1zFGnp8pEIY2W9m/jD+bPQqbZIvd4awImvA3Ptu8JRO J/MFgiJrlXah2ZXmqHFaf9uyIp0h6+8AWSDO5N8WOAZWc1io7Qrd7nsJVLZmya0q1w+U 0Dzg== X-Gm-Message-State: AOJu0Yxox9wRLiGKSaImVdqgplL0jcSkGWgOkmTUQdQAe3Ra6Hls8iQJ bD2wYXYWjCl2Qq1XP0pdzCs= X-Google-Smtp-Source: AGHT+IHnKWzQFwWjncnq+LJF9uTpmTGhQ5MOlEolE2p/d6tyeSEeoFso6zN4m8vhXGlIoVjp1dnATQ== X-Received: by 2002:a05:6359:d06:b0:16b:c63d:5dfe with SMTP id gp6-20020a0563590d0600b0016bc63d5dfemr318506rwb.16.1699670989378; Fri, 10 Nov 2023 18:49:49 -0800 (PST) Received: from localhost ([2620:10d:c090:400::4:7384]) by smtp.gmail.com with ESMTPSA id u5-20020a656705000000b00584aff3060dsm327335pgf.59.2023.11.10.18.49.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 10 Nov 2023 18:49:48 -0800 (PST) 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, changwoo@igalia.com, himadrics@inria.fr, memxor@gmail.com Cc: linux-kernel@vger.kernel.org, bpf@vger.kernel.org, kernel-team@meta.com, Tejun Heo Subject: [PATCH 28/36] sched_ext: Implement SCX_KICK_WAIT Date: Fri, 10 Nov 2023 16:47:54 -1000 Message-ID: <20231111024835.2164816-29-tj@kernel.org> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20231111024835.2164816-1-tj@kernel.org> References: <20231111024835.2164816-1-tj@kernel.org> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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_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 2dea64a52157..9fe1a224c888 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6077,8 +6077,10 @@ __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 e4aa935006bc..76a90b2c1662 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -132,6 +132,9 @@ static struct { #endif /* CONFIG_SMP */ +/* for %SCX_KICK_WAIT */ +static unsigned long __percpu *scx_kick_cpus_pnt_seqs; + /* * Direct dispatch marker. * @@ -3280,6 +3283,7 @@ 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(); + unsigned long *pseqs = this_cpu_ptr(scx_kick_cpus_pnt_seqs); int this_cpu = cpu_of(this_rq); int cpu; @@ -3293,14 +3297,32 @@ 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); } /** @@ -3359,7 +3381,7 @@ 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); @@ -3367,6 +3389,12 @@ 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); @@ -3375,6 +3403,7 @@ 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); } @@ -3641,6 +3670,8 @@ 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 94e788ab56d9..00218d43d887 100644 --- a/kernel/sched/ext.h +++ b/kernel/sched/ext.h @@ -65,6 +65,7 @@ enum scx_pick_idle_cpu_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 */ }; enum scx_tg_flags { @@ -115,6 +116,22 @@ __printf(2, 3) void scx_ops_error_kind(enum scx_exit_kind kind, #define scx_ops_error(fmt, args...) \ scx_ops_error_kind(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; @@ -170,6 +187,9 @@ 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 9f1f2e778683..f889833371a2 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -697,6 +697,8 @@ struct scx_rq { u32 flags; cpumask_var_t cpus_to_kick; cpumask_var_t cpus_to_preempt; + cpumask_var_t cpus_to_wait; + unsigned long pnt_seq; struct irq_work kick_cpus_irq_work; }; #endif /* CONFIG_SCHED_CLASS_EXT */