From patchwork Wed Nov 30 08:23:07 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tejun Heo X-Patchwork-Id: 13059559 X-Patchwork-Delegate: bpf@iogearbox.net Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 95269C352A1 for ; Wed, 30 Nov 2022 08:27:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234858AbiK3I1I (ORCPT ); Wed, 30 Nov 2022 03:27:08 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55966 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235226AbiK3IZk (ORCPT ); Wed, 30 Nov 2022 03:25:40 -0500 Received: from mail-pj1-x1030.google.com (mail-pj1-x1030.google.com [IPv6:2607:f8b0:4864:20::1030]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A51E67047A; Wed, 30 Nov 2022 00:24:31 -0800 (PST) Received: by mail-pj1-x1030.google.com with SMTP id o12so7208237pjo.4; Wed, 30 Nov 2022 00:24:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; 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=icbEL6Yyh88UwKlWIMibQXf09tYG4jVGd0Sd4NYusRk=; b=cwevkODSfgy/ecZgn1k9Sl3axSX97jP3z2nxUdls+f3M+9XG9jOSmyTeNQioc3Oih/ xnhqxcRW67kGSuIu4oa/20EDH5zCBGY/CoRZLTDXxRZvatLVoqEY99RmTc0CcwmW1Z+o H3ucNRMQanqy8GVJv9CU7u9JohFhNWWYT1jD5UT9gsIfNScLNUw3IZB7X2CoETDsmuHY eL8ju2tQjY4NQmmlfR4/smloVFDKwtC1WswsrbyTN/oBtrJXyhHZyxH819kHtmbIBQGm frocUBnuSV/ZMRlPAJsnA6irxxhKS9FGbpOcRiZreHnMoEqMcWslMZI6kR3TqrSnFOgv /7UA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; 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=icbEL6Yyh88UwKlWIMibQXf09tYG4jVGd0Sd4NYusRk=; b=lu0nj3hvLfj23dqw0xD46o9Lg2QvJXzrr/GNYjHcdZhDrYUI2HRhkqJgKVZzmSuPnP 0IyTXDtwgSb81hDOI8DG7LVc2YjFeZ4ir8fkF7G4m8MxHD4MjKa/VaZuzbOT4Hvwlww/ 6BRe3LaH8lwkjdiyzm0MBCah+jkTW8BT7h91aq3frco5fYo8xIBh1sA0FvNU/BrgcOlx zC7+FkB4W/t6587MsQaJZNCoLCXnICTzPbgdGzQuvoDQC6EwcGSLTWLh+Nu11rNO0UWN +1IEWRWNzUF+2r65DrHxrNjtYEZ1hoea0M+wHOGnzpj5Q5IyYQjW/2b2cljvsqGsfKri Ga7A== X-Gm-Message-State: ANoB5pn7VID3NFhMPA2fpyIf/Bc3rs2kOSgu+vGnxYi4npm7gwaRo4y3 QDuDGwos6SPHMbwwwYBoa7A= X-Google-Smtp-Source: AA0mqf4IlcoridLQ++OjRdvy1H/e5LzA5fityT9BR15abVAoR90Rh0qY8hdmHjRCpcdgu7gGeuvKMg== X-Received: by 2002:a17:902:bf01:b0:186:8bca:1d50 with SMTP id bi1-20020a170902bf0100b001868bca1d50mr42720977plb.158.1669796670788; Wed, 30 Nov 2022 00:24:30 -0800 (PST) Received: from localhost ([2600:380:4a00:1415:d028:b547:7d35:7b0b]) by smtp.gmail.com with ESMTPSA id u6-20020a170902e80600b0017849a2b56asm777944plg.46.2022.11.30.00.24.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Nov 2022 00:24:30 -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 Cc: linux-kernel@vger.kernel.org, bpf@vger.kernel.org, kernel-team@meta.com, Tejun Heo Subject: [PATCH 25/31] sched_ext: Implement SCX_KICK_WAIT Date: Tue, 29 Nov 2022 22:23:07 -1000 Message-Id: <20221130082313.3241517-26-tj@kernel.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221130082313.3241517-1-tj@kernel.org> References: <20221130082313.3241517-1-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 | 36 ++++++++++++++++++++++++++++++++++-- kernel/sched/ext.h | 20 ++++++++++++++++++++ kernel/sched/sched.h | 2 ++ 4 files changed, 59 insertions(+), 3 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 79560641a61f..ea4f6edfcf32 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5886,8 +5886,10 @@ __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 bd03b55fbcf5..aeaad3d8b05a 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -109,8 +109,9 @@ unsigned long last_timeout_check = INITIAL_JIFFIES; static struct delayed_work check_timeout_work; -/* idle tracking */ #ifdef CONFIG_SMP + +/* idle tracking */ #ifdef CONFIG_CPUMASK_OFFSTACK #define CL_ALIGNED_IF_ONSTACK #else @@ -123,7 +124,11 @@ static struct { } idle_masks CL_ALIGNED_IF_ONSTACK; static bool __cacheline_aligned_in_smp has_idle_cpus; -#endif + +/* for %SCX_KICK_WAIT */ +static u64 __percpu *kick_cpus_pnt_seqs; + +#endif /* CONFIG_SMP */ /* * Direct dispatch marker. @@ -2959,6 +2964,7 @@ 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(kick_cpus_pnt_seqs); int this_cpu = cpu_of(this_rq); int cpu; @@ -2972,14 +2978,32 @@ 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); } #endif @@ -2999,6 +3023,11 @@ void __init init_sched_ext_class(void) #ifdef CONFIG_SMP BUG_ON(!alloc_cpumask_var(&idle_masks.cpu, GFP_KERNEL)); BUG_ON(!alloc_cpumask_var(&idle_masks.smt, GFP_KERNEL)); + + kick_cpus_pnt_seqs = __alloc_percpu(sizeof(kick_cpus_pnt_seqs[0]) * + num_possible_cpus(), + __alignof__(kick_cpus_pnt_seqs[0])); + BUG_ON(!kick_cpus_pnt_seqs); #endif for_each_possible_cpu(cpu) { struct rq *rq = cpu_rq(cpu); @@ -3009,6 +3038,7 @@ void __init init_sched_ext_class(void) #ifdef CONFIG_SMP 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); #endif } @@ -3228,6 +3258,8 @@ 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 470b2224cdfa..8ae717c5e850 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 @@ -107,6 +108,22 @@ __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, timeout; @@ -164,6 +181,9 @@ 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 a2ffa94ede02..5af758cc1e38 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -714,6 +714,8 @@ struct scx_rq { #ifdef CONFIG_SMP 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 };