From nobody Tue Dec 16 21:59:12 2025 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 791BF24BCE9 for ; Mon, 10 Feb 2025 15:33:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739201605; cv=none; b=ClN5Z3fMZpv3H0xNvLLYMh+8MpsqSERzAhG142fUhJ1B+Ssv3FlXXrMofEzKMJjpgz7AHhCeWd+JUtp/3KU/JSf7XiwKnKBdfMKYqIRObOhqUNcU4tIn4crCM9NmrjaL3jP3L7y5qrxOdRrk2x+Miqu+TZfNwuhSsJ+IZ5d+bQs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739201605; c=relaxed/simple; bh=hXKMFjUxmniwLPmXl/zrhJcXY2dfco4gVE9XyWgbOhs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ei40++OPW4gTav4fJkH9e0QDdL5PL7+BT6/0Mcm6vdtf09Tt521gJN+uPzgI4Buo00XMDSNtIZZ3TNiv4T5JoHYk3NMqDPsOUbUc0yNG5GBd/RHRydwlqqNQfLYQEsfRFKW+fRJdnAK5b+HjF3Duf7nhmp0+ze9zAwVUw9a6J7E= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=AZcGtqO8; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="AZcGtqO8" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1739201602; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=5B84Awu6JUpstdhEM0yzA51Ej2LPUV/BX8OiM6ds56M=; b=AZcGtqO8LiLbCqFqYoP1gnQohLd+I8NzM7srrv15WS2iMYc++IKASArPQij/54ILIVOqFw i4Lmc8Ho6HH7sQcQfbJm0aiBn6TYs1VciGjm1VRWTRhoAKgd8CU4Fb4m6mwCo5U+2qhAuf EjN7hqtWuRpqLhOyJ5FKE2Q0voayQ8w= Received: from mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-377-b9b0u06MOzOGh5KpIVY7hQ-1; Mon, 10 Feb 2025 10:33:16 -0500 X-MC-Unique: b9b0u06MOzOGh5KpIVY7hQ-1 X-Mimecast-MFC-AGG-ID: b9b0u06MOzOGh5KpIVY7hQ Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id F40821955D5C; Mon, 10 Feb 2025 15:33:14 +0000 (UTC) Received: from gmonaco-thinkpadt14gen3.rmtit.com (unknown [10.44.34.65]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 73CDE18004A7; Mon, 10 Feb 2025 15:33:10 +0000 (UTC) From: Gabriele Monaco To: linux-kernel@vger.kernel.org, Andrew Morton , Ingo Molnar , Peter Zijlstra , linux-mm@kvack.org Cc: Mathieu Desnoyers , Marco Elver , Ingo Molnar , Gabriele Monaco , "Paul E. McKenney" , Shuah Khan Subject: [PATCH v6 1/3] sched: Compact RSEQ concurrency IDs with reduced threads and affinity Date: Mon, 10 Feb 2025 16:32:50 +0100 Message-ID: <20250210153253.460471-2-gmonaco@redhat.com> In-Reply-To: <20250210153253.460471-1-gmonaco@redhat.com> References: <20250210153253.460471-1-gmonaco@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Content-Type: text/plain; charset="utf-8" From: Mathieu Desnoyers When a process reduces its number of threads or clears bits in its CPU affinity mask, the mm_cid allocation should eventually converge towards smaller values. However, the change introduced by: commit 7e019dcc470f ("sched: Improve cache locality of RSEQ concurrency IDs for intermittent workloads") adds a per-mm/CPU recent_cid which is never unset unless a thread migrates. This is a tradeoff between: A) Preserving cache locality after a transition from many threads to few threads, or after reducing the hamming weight of the allowed CPU mask. B) Making the mm_cid upper bounds wrt nr threads and allowed CPU mask easy to document and understand. C) Allowing applications to eventually react to mm_cid compaction after reduction of the nr threads or allowed CPU mask, making the tracking of mm_cid compaction easier by shrinking it back towards 0 or not. D) Making sure applications that periodically reduce and then increase again the nr threads or allowed CPU mask still benefit from good cache locality with mm_cid. Introduce the following changes: * After shrinking the number of threads or reducing the number of allowed CPUs, reduce the value of max_nr_cid so expansion of CID allocation will preserve cache locality if the number of threads or allowed CPUs increase again. * Only re-use a recent_cid if it is within the max_nr_cid upper bound, else find the first available CID. Fixes: 7e019dcc470f ("sched: Improve cache locality of RSEQ concurrency IDs= for intermittent workloads") Cc: Peter Zijlstra (Intel) Cc: Marco Elver Cc: Ingo Molnar Tested-by: Gabriele Monaco Signed-off-by: Mathieu Desnoyers Signed-off-by: Gabriele Monaco --- include/linux/mm_types.h | 7 ++++--- kernel/sched/sched.h | 25 ++++++++++++++++++++++--- 2 files changed, 26 insertions(+), 6 deletions(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 6b27db7f94963..0234f14f2aa6b 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -875,10 +875,11 @@ struct mm_struct { */ unsigned int nr_cpus_allowed; /** - * @max_nr_cid: Maximum number of concurrency IDs allocated. + * @max_nr_cid: Maximum number of allowed concurrency + * IDs allocated. * - * Track the highest number of concurrency IDs allocated for the - * mm. + * Track the highest number of allowed concurrency IDs + * allocated for the mm. */ atomic_t max_nr_cid; /** diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 38e0e323dda26..606c96b74ebfa 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -3698,10 +3698,28 @@ static inline int __mm_cid_try_get(struct task_stru= ct *t, struct mm_struct *mm) { struct cpumask *cidmask =3D mm_cidmask(mm); struct mm_cid __percpu *pcpu_cid =3D mm->pcpu_cid; - int cid =3D __this_cpu_read(pcpu_cid->recent_cid); + int cid, max_nr_cid, allowed_max_nr_cid; =20 + /* + * After shrinking the number of threads or reducing the number + * of allowed cpus, reduce the value of max_nr_cid so expansion + * of cid allocation will preserve cache locality if the number + * of threads or allowed cpus increase again. + */ + max_nr_cid =3D atomic_read(&mm->max_nr_cid); + while ((allowed_max_nr_cid =3D min_t(int, READ_ONCE(mm->nr_cpus_allowed), + atomic_read(&mm->mm_users))), + max_nr_cid > allowed_max_nr_cid) { + /* atomic_try_cmpxchg loads previous mm->max_nr_cid into max_nr_cid. */ + if (atomic_try_cmpxchg(&mm->max_nr_cid, &max_nr_cid, allowed_max_nr_cid)= ) { + max_nr_cid =3D allowed_max_nr_cid; + break; + } + } /* Try to re-use recent cid. This improves cache locality. */ - if (!mm_cid_is_unset(cid) && !cpumask_test_and_set_cpu(cid, cidmask)) + cid =3D __this_cpu_read(pcpu_cid->recent_cid); + if (!mm_cid_is_unset(cid) && cid < max_nr_cid && + !cpumask_test_and_set_cpu(cid, cidmask)) return cid; /* * Expand cid allocation if the maximum number of concurrency @@ -3709,8 +3727,9 @@ static inline int __mm_cid_try_get(struct task_struct= *t, struct mm_struct *mm) * and number of threads. Expanding cid allocation as much as * possible improves cache locality. */ - cid =3D atomic_read(&mm->max_nr_cid); + cid =3D max_nr_cid; while (cid < READ_ONCE(mm->nr_cpus_allowed) && cid < atomic_read(&mm->mm_= users)) { + /* atomic_try_cmpxchg loads previous mm->max_nr_cid into cid. */ if (!atomic_try_cmpxchg(&mm->max_nr_cid, &cid, cid + 1)) continue; if (!cpumask_test_and_set_cpu(cid, cidmask)) --=20 2.48.1 From nobody Tue Dec 16 21:59:12 2025 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 BA24623E251 for ; Mon, 10 Feb 2025 15:33:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739201610; cv=none; b=fWaES8KL6QeVyRuLKkvmtc5Jrb8GsDVA+mDrwu4T+8DIzGfhXgFF2h6fWSubVLP3zZR52I88qMN1Ett7XBLrSdVB55Oj3wNFzjldpGXGffYwNIFZQ1DLu+xCvBUC03GKwm5n57v2P6P29vtls+0hDGKW1Un40F2CL7gBL41+A08= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739201610; c=relaxed/simple; bh=9Rwb0Zy0TFYVzR/n/xQHWwS/ZMTa05qSikjypC3FsLY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=kYwg8XuwAi1A3GTZ/AevDy/vba3wHqOVoExIzi5d8Gcpli60csh5UHPA5Mum/tX/XxrXKn3aiPsXGsg6N8gymZ0BxGa/dgn1Az9I5t2oOTerHEZ3jS5J1QNbjqEbRlpwSVCsvmWObK5rPxNggadfYr2iD8QtdlhjzudHXWYXTM8= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=W2O2eBD3; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="W2O2eBD3" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1739201607; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=191fmzOplUZF3eh9uENAPy4J7EnijRk6+X9V7IdEjDw=; b=W2O2eBD3E8pjhmYSE8GEGr8/XD7u8OHOXC5HitoXJTMk1iv6Pb+nl9AjgNmUS30iAQUha6 AxCRxpHn8IWnxjUpaF46unkVeNr7ofs3LmpZaFx2qI/BoPs9NWu1LNq9ObaVht2FbjkN8U Uv200T5SdStclJn8GT1NG6B2+R2+aOM= Received: from mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-209-x8Sp5xoAOn6BdzEqQLm_KQ-1; Mon, 10 Feb 2025 10:33:21 -0500 X-MC-Unique: x8Sp5xoAOn6BdzEqQLm_KQ-1 X-Mimecast-MFC-AGG-ID: x8Sp5xoAOn6BdzEqQLm_KQ Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 910BD1955DDD; Mon, 10 Feb 2025 15:33:19 +0000 (UTC) Received: from gmonaco-thinkpadt14gen3.rmtit.com (unknown [10.44.34.65]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id ACA0118004A7; Mon, 10 Feb 2025 15:33:15 +0000 (UTC) From: Gabriele Monaco To: linux-kernel@vger.kernel.org, Andrew Morton , Ingo Molnar , Peter Zijlstra , linux-mm@kvack.org Cc: Gabriele Monaco , Mathieu Desnoyers , Ingo Molnar , "Paul E. McKenney" , Shuah Khan Subject: [PATCH v6 2/3] sched: Move task_mm_cid_work to mm delayed work Date: Mon, 10 Feb 2025 16:32:51 +0100 Message-ID: <20250210153253.460471-3-gmonaco@redhat.com> In-Reply-To: <20250210153253.460471-1-gmonaco@redhat.com> References: <20250210153253.460471-1-gmonaco@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Content-Type: text/plain; charset="utf-8" Currently, the task_mm_cid_work function is called in a task work triggered by a scheduler tick to frequently compact the mm_cids of each process. This can delay the execution of the corresponding thread for the entire duration of the function, negatively affecting the response in case of real time tasks. In practice, we observe task_mm_cid_work increasing the latency of 30-35us on a 128 cores system, this order of magnitude is meaningful under PREEMPT_RT. Run the task_mm_cid_work in a new delayed work connected to the mm_struct rather than in the task context before returning to userspace. This delayed work is initialised while allocating the mm and disabled before freeing it, its execution is no longer triggered by scheduler ticks but run periodically based on the defined MM_CID_SCAN_DELAY. The main advantage of this change is that the function can be offloaded to a different CPU and even preempted by RT tasks. Moreover, this new behaviour could be more predictable with periodic tasks with short runtime, which may rarely run during a scheduler tick. Now, the work is always scheduled with the same periodicity for each mm (though the periodicity is not guaranteed due to interference from other tasks, but mm_cid compaction is mostly best effort). To avoid excessively increased runtime, we quickly return from the function if we have no work to be done (i.e. no mm_cid is allocated). This is helpful for tasks that sleep for a long time, but also for terminated task. We are no longer following the process' state, hence the function continues to run after a process terminates but before its mm is freed. Fixes: 223baf9d17f2 ("sched: Fix performance regression introduced by mm_ci= d") Reviewed-by: Mathieu Desnoyers Signed-off-by: Gabriele Monaco --- include/linux/mm_types.h | 16 ++++++---- include/linux/sched.h | 1 - kernel/sched/core.c | 66 +++++----------------------------------- kernel/sched/sched.h | 7 ----- 4 files changed, 18 insertions(+), 72 deletions(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 0234f14f2aa6b..3aeadb519cac5 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -861,12 +861,6 @@ struct mm_struct { * runqueue locks. */ struct mm_cid __percpu *pcpu_cid; - /* - * @mm_cid_next_scan: Next mm_cid scan (in jiffies). - * - * When the next mm_cid scan is due (in jiffies). - */ - unsigned long mm_cid_next_scan; /** * @nr_cpus_allowed: Number of CPUs allowed for mm. * @@ -889,6 +883,7 @@ struct mm_struct { * mm nr_cpus_allowed updates. */ raw_spinlock_t cpus_allowed_lock; + struct delayed_work mm_cid_work; #endif #ifdef CONFIG_MMU atomic_long_t pgtables_bytes; /* size of all page tables */ @@ -1180,11 +1175,16 @@ static inline void vma_iter_init(struct vma_iterato= r *vmi, =20 #ifdef CONFIG_SCHED_MM_CID =20 +#define SCHED_MM_CID_PERIOD_NS (100ULL * 1000000) /* 100ms */ +#define MM_CID_SCAN_DELAY 100 /* 100ms */ + enum mm_cid_state { MM_CID_UNSET =3D -1U, /* Unset state has lazy_put flag set. */ MM_CID_LAZY_PUT =3D (1U << 31), }; =20 +extern void task_mm_cid_work(struct work_struct *work); + static inline bool mm_cid_is_unset(int cid) { return cid =3D=3D MM_CID_UNSET; @@ -1257,12 +1257,16 @@ static inline int mm_alloc_cid_noprof(struct mm_str= uct *mm, struct task_struct * if (!mm->pcpu_cid) return -ENOMEM; mm_init_cid(mm, p); + INIT_DELAYED_WORK(&mm->mm_cid_work, task_mm_cid_work); + schedule_delayed_work(&mm->mm_cid_work, + msecs_to_jiffies(MM_CID_SCAN_DELAY)); return 0; } #define mm_alloc_cid(...) alloc_hooks(mm_alloc_cid_noprof(__VA_ARGS__)) =20 static inline void mm_destroy_cid(struct mm_struct *mm) { + disable_delayed_work_sync(&mm->mm_cid_work); free_percpu(mm->pcpu_cid); mm->pcpu_cid =3D NULL; } diff --git a/include/linux/sched.h b/include/linux/sched.h index 9632e3318e0d6..515b15f946cac 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1397,7 +1397,6 @@ struct task_struct { int last_mm_cid; /* Most recent cid in mm */ int migrate_from_cpu; int mm_cid_active; /* Whether cid bitmap is active */ - struct callback_head cid_work; #endif =20 struct tlbflush_unmap_batch tlb_ubc; diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 165c90ba64ea9..c65003ab8c55b 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4524,7 +4524,6 @@ static void __sched_fork(unsigned long clone_flags, s= truct task_struct *p) p->wake_entry.u_flags =3D CSD_TYPE_TTWU; p->migration_pending =3D NULL; #endif - init_sched_mm_cid(p); } =20 DEFINE_STATIC_KEY_FALSE(sched_numa_balancing); @@ -5662,7 +5661,6 @@ void sched_tick(void) resched_latency =3D cpu_resched_latency(rq); calc_global_load_tick(rq); sched_core_tick(rq); - task_tick_mm_cid(rq, donor); scx_tick(rq); =20 rq_unlock(rq, &rf); @@ -10528,38 +10526,17 @@ static void sched_mm_cid_remote_clear_weight(stru= ct mm_struct *mm, int cpu, sched_mm_cid_remote_clear(mm, pcpu_cid, cpu); } =20 -static void task_mm_cid_work(struct callback_head *work) +void task_mm_cid_work(struct work_struct *work) { - unsigned long now =3D jiffies, old_scan, next_scan; - struct task_struct *t =3D current; struct cpumask *cidmask; - struct mm_struct *mm; + struct delayed_work *delayed_work =3D container_of(work, struct delayed_w= ork, work); + struct mm_struct *mm =3D container_of(delayed_work, struct mm_struct, mm_= cid_work); int weight, cpu; =20 - SCHED_WARN_ON(t !=3D container_of(work, struct task_struct, cid_work)); - - work->next =3D work; /* Prevent double-add */ - if (t->flags & PF_EXITING) - return; - mm =3D t->mm; - if (!mm) - return; - old_scan =3D READ_ONCE(mm->mm_cid_next_scan); - next_scan =3D now + msecs_to_jiffies(MM_CID_SCAN_DELAY); - if (!old_scan) { - unsigned long res; - - res =3D cmpxchg(&mm->mm_cid_next_scan, old_scan, next_scan); - if (res !=3D old_scan) - old_scan =3D res; - else - old_scan =3D next_scan; - } - if (time_before(now, old_scan)) - return; - if (!try_cmpxchg(&mm->mm_cid_next_scan, &old_scan, next_scan)) - return; cidmask =3D mm_cidmask(mm); + /* Nothing to clear for now */ + if (cpumask_empty(cidmask)) + goto out; /* Clear cids that were not recently used. */ for_each_possible_cpu(cpu) sched_mm_cid_remote_clear_old(mm, cpu); @@ -10570,35 +10547,8 @@ static void task_mm_cid_work(struct callback_head = *work) */ for_each_possible_cpu(cpu) sched_mm_cid_remote_clear_weight(mm, cpu, weight); -} - -void init_sched_mm_cid(struct task_struct *t) -{ - struct mm_struct *mm =3D t->mm; - int mm_users =3D 0; - - if (mm) { - mm_users =3D atomic_read(&mm->mm_users); - if (mm_users =3D=3D 1) - mm->mm_cid_next_scan =3D jiffies + msecs_to_jiffies(MM_CID_SCAN_DELAY); - } - t->cid_work.next =3D &t->cid_work; /* Protect against double add */ - init_task_work(&t->cid_work, task_mm_cid_work); -} - -void task_tick_mm_cid(struct rq *rq, struct task_struct *curr) -{ - struct callback_head *work =3D &curr->cid_work; - unsigned long now =3D jiffies; - - if (!curr->mm || (curr->flags & (PF_EXITING | PF_KTHREAD)) || - work->next !=3D work) - return; - if (time_before(now, READ_ONCE(curr->mm->mm_cid_next_scan))) - return; - - /* No page allocation under rq lock */ - task_work_add(curr, work, TWA_RESUME); +out: + schedule_delayed_work(delayed_work, msecs_to_jiffies(MM_CID_SCAN_DELAY)); } =20 void sched_mm_cid_exit_signals(struct task_struct *t) diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 606c96b74ebfa..fc613d9090bed 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -3622,16 +3622,11 @@ extern void sched_dynamic_update(int mode); =20 #ifdef CONFIG_SCHED_MM_CID =20 -#define SCHED_MM_CID_PERIOD_NS (100ULL * 1000000) /* 100ms */ -#define MM_CID_SCAN_DELAY 100 /* 100ms */ - extern raw_spinlock_t cid_lock; extern int use_cid_lock; =20 extern void sched_mm_cid_migrate_from(struct task_struct *t); extern void sched_mm_cid_migrate_to(struct rq *dst_rq, struct task_struct = *t); -extern void task_tick_mm_cid(struct rq *rq, struct task_struct *curr); -extern void init_sched_mm_cid(struct task_struct *t); =20 static inline void __mm_cid_put(struct mm_struct *mm, int cid) { @@ -3899,8 +3894,6 @@ static inline void switch_mm_cid(struct rq *rq, static inline void switch_mm_cid(struct rq *rq, struct task_struct *prev, = struct task_struct *next) { } static inline void sched_mm_cid_migrate_from(struct task_struct *t) { } static inline void sched_mm_cid_migrate_to(struct rq *dst_rq, struct task_= struct *t) { } -static inline void task_tick_mm_cid(struct rq *rq, struct task_struct *cur= r) { } -static inline void init_sched_mm_cid(struct task_struct *t) { } #endif /* !CONFIG_SCHED_MM_CID */ =20 extern u64 avg_vruntime(struct cfs_rq *cfs_rq); --=20 2.48.1 From nobody Tue Dec 16 21:59:12 2025 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 45D5B23CF15 for ; 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Mon, 10 Feb 2025 10:33:26 -0500 X-MC-Unique: kGn09XMQOEurUM2gVyKo4w-1 X-Mimecast-MFC-AGG-ID: kGn09XMQOEurUM2gVyKo4w Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 88C1119560B1; Mon, 10 Feb 2025 15:33:23 +0000 (UTC) Received: from gmonaco-thinkpadt14gen3.rmtit.com (unknown [10.44.34.65]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 6F4C61800876; Mon, 10 Feb 2025 15:33:20 +0000 (UTC) From: Gabriele Monaco To: linux-kernel@vger.kernel.org, Mathieu Desnoyers , Peter Zijlstra , "Paul E. McKenney" , Shuah Khan , linux-kselftest@vger.kernel.org Cc: Gabriele Monaco , Ingo Molnar Subject: [PATCH v6 3/3] rseq/selftests: Add test for mm_cid compaction Date: Mon, 10 Feb 2025 16:32:52 +0100 Message-ID: <20250210153253.460471-4-gmonaco@redhat.com> In-Reply-To: <20250210153253.460471-1-gmonaco@redhat.com> References: <20250210153253.460471-1-gmonaco@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Content-Type: text/plain; charset="utf-8" A task in the kernel (task_mm_cid_work) runs somewhat periodically to compact the mm_cid for each process. Add a test to validate that it runs correctly and timely. The test spawns 1 thread pinned to each CPU, then each thread, including the main one, runs in short bursts for some time. During this period, the mm_cids should be spanning all numbers between 0 and nproc. At the end of this phase, a thread with high enough mm_cid (>=3D nproc/2) is selected to be the new leader, all other threads terminate. After some time, the only running thread should see 0 as mm_cid, if that doesn't happen, the compaction mechanism didn't work and the test fails. The test never fails if only 1 core is available, in which case, we cannot test anything as the only available mm_cid is 0. Reviewed-by: Mathieu Desnoyers Signed-off-by: Gabriele Monaco --- tools/testing/selftests/rseq/.gitignore | 1 + tools/testing/selftests/rseq/Makefile | 2 +- .../selftests/rseq/mm_cid_compaction_test.c | 200 ++++++++++++++++++ 3 files changed, 202 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/rseq/mm_cid_compaction_test.c diff --git a/tools/testing/selftests/rseq/.gitignore b/tools/testing/selfte= sts/rseq/.gitignore index 16496de5f6ce4..2c89f97e4f737 100644 --- a/tools/testing/selftests/rseq/.gitignore +++ b/tools/testing/selftests/rseq/.gitignore @@ -3,6 +3,7 @@ basic_percpu_ops_test basic_percpu_ops_mm_cid_test basic_test basic_rseq_op_test +mm_cid_compaction_test param_test param_test_benchmark param_test_compare_twice diff --git a/tools/testing/selftests/rseq/Makefile b/tools/testing/selftest= s/rseq/Makefile index 5a3432fceb586..ce1b38f46a355 100644 --- a/tools/testing/selftests/rseq/Makefile +++ b/tools/testing/selftests/rseq/Makefile @@ -16,7 +16,7 @@ OVERRIDE_TARGETS =3D 1 =20 TEST_GEN_PROGS =3D basic_test basic_percpu_ops_test basic_percpu_ops_mm_ci= d_test param_test \ param_test_benchmark param_test_compare_twice param_test_mm_cid \ - param_test_mm_cid_benchmark param_test_mm_cid_compare_twice + param_test_mm_cid_benchmark param_test_mm_cid_compare_twice mm_cid_compa= ction_test =20 TEST_GEN_PROGS_EXTENDED =3D librseq.so =20 diff --git a/tools/testing/selftests/rseq/mm_cid_compaction_test.c b/tools/= testing/selftests/rseq/mm_cid_compaction_test.c new file mode 100644 index 0000000000000..7ddde3b657dd6 --- /dev/null +++ b/tools/testing/selftests/rseq/mm_cid_compaction_test.c @@ -0,0 +1,200 @@ +// SPDX-License-Identifier: LGPL-2.1 +#define _GNU_SOURCE +#include +#include +#include +#include +#include +#include +#include +#include + +#include "../kselftest.h" +#include "rseq.h" + +#define VERBOSE 0 +#define printf_verbose(fmt, ...) \ + do { \ + if (VERBOSE) \ + printf(fmt, ##__VA_ARGS__); \ + } while (0) + +/* 0.5 s */ +#define RUNNER_PERIOD 500000 +/* Number of runs before we terminate or get the token */ +#define THREAD_RUNS 5 + +/* + * Number of times we check that the mm_cid were compacted. + * Checks are repeated every RUNNER_PERIOD. + */ +#define MM_CID_COMPACT_TIMEOUT 10 + +struct thread_args { + int cpu; + int num_cpus; + pthread_mutex_t *token; + pthread_barrier_t *barrier; + pthread_t *tinfo; + struct thread_args *args_head; +}; + +static void __noreturn *thread_runner(void *arg) +{ + struct thread_args *args =3D arg; + int i, ret, curr_mm_cid; + cpu_set_t cpumask; + + CPU_ZERO(&cpumask); + CPU_SET(args->cpu, &cpumask); + ret =3D pthread_setaffinity_np(pthread_self(), sizeof(cpumask), &cpumask); + if (ret) { + errno =3D ret; + perror("Error: failed to set affinity"); + abort(); + } + pthread_barrier_wait(args->barrier); + + for (i =3D 0; i < THREAD_RUNS; i++) + usleep(RUNNER_PERIOD); + curr_mm_cid =3D rseq_current_mm_cid(); + /* + * We select one thread with high enough mm_cid to be the new leader. + * All other threads (including the main thread) will terminate. + * After some time, the mm_cid of the only remaining thread should + * converge to 0, if not, the test fails. + */ + if (curr_mm_cid >=3D args->num_cpus / 2 && + !pthread_mutex_trylock(args->token)) { + printf_verbose( + "cpu%d has mm_cid=3D%d and will be the new leader.\n", + sched_getcpu(), curr_mm_cid); + for (i =3D 0; i < args->num_cpus; i++) { + if (args->tinfo[i] =3D=3D pthread_self()) + continue; + ret =3D pthread_join(args->tinfo[i], NULL); + if (ret) { + errno =3D ret; + perror("Error: failed to join thread"); + abort(); + } + } + pthread_barrier_destroy(args->barrier); + free(args->tinfo); + free(args->token); + free(args->barrier); + free(args->args_head); + + for (i =3D 0; i < MM_CID_COMPACT_TIMEOUT; i++) { + curr_mm_cid =3D rseq_current_mm_cid(); + printf_verbose("run %d: mm_cid=3D%d on cpu%d.\n", i, + curr_mm_cid, sched_getcpu()); + if (curr_mm_cid =3D=3D 0) + exit(EXIT_SUCCESS); + usleep(RUNNER_PERIOD); + } + exit(EXIT_FAILURE); + } + printf_verbose("cpu%d has mm_cid=3D%d and is going to terminate.\n", + sched_getcpu(), curr_mm_cid); + pthread_exit(NULL); +} + +int test_mm_cid_compaction(void) +{ + cpu_set_t affinity; + int i, j, ret =3D 0, num_threads; + pthread_t *tinfo; + pthread_mutex_t *token; + pthread_barrier_t *barrier; + struct thread_args *args; + + sched_getaffinity(0, sizeof(affinity), &affinity); + num_threads =3D CPU_COUNT(&affinity); + tinfo =3D calloc(num_threads, sizeof(*tinfo)); + if (!tinfo) { + perror("Error: failed to allocate tinfo"); + return -1; + } + args =3D calloc(num_threads, sizeof(*args)); + if (!args) { + perror("Error: failed to allocate args"); + ret =3D -1; + goto out_free_tinfo; + } + token =3D malloc(sizeof(*token)); + if (!token) { + perror("Error: failed to allocate token"); + ret =3D -1; + goto out_free_args; + } + barrier =3D malloc(sizeof(*barrier)); + if (!barrier) { + perror("Error: failed to allocate barrier"); + ret =3D -1; + goto out_free_token; + } + if (num_threads =3D=3D 1) { + fprintf(stderr, "Cannot test on a single cpu. " + "Skipping mm_cid_compaction test.\n"); + /* only skipping the test, this is not a failure */ + goto out_free_barrier; + } + pthread_mutex_init(token, NULL); + ret =3D pthread_barrier_init(barrier, NULL, num_threads); + if (ret) { + errno =3D ret; + perror("Error: failed to initialise barrier"); + goto out_free_barrier; + } + for (i =3D 0, j =3D 0; i < CPU_SETSIZE && j < num_threads; i++) { + if (!CPU_ISSET(i, &affinity)) + continue; + args[j].num_cpus =3D num_threads; + args[j].tinfo =3D tinfo; + args[j].token =3D token; + args[j].barrier =3D barrier; + args[j].cpu =3D i; + args[j].args_head =3D args; + if (!j) { + /* The first thread is the main one */ + tinfo[0] =3D pthread_self(); + ++j; + continue; + } + ret =3D pthread_create(&tinfo[j], NULL, thread_runner, &args[j]); + if (ret) { + errno =3D ret; + perror("Error: failed to create thread"); + abort(); + } + ++j; + } + printf_verbose("Started %d threads.\n", num_threads); + + /* Also main thread will terminate if it is not selected as leader */ + thread_runner(&args[0]); + + /* only reached in case of errors */ +out_free_barrier: + free(barrier); +out_free_token: + free(token); +out_free_args: + free(args); +out_free_tinfo: + free(tinfo); + + return ret; +} + +int main(int argc, char **argv) +{ + if (!rseq_mm_cid_available()) { + fprintf(stderr, "Error: rseq_mm_cid unavailable\n"); + return -1; + } + if (test_mm_cid_compaction()) + return -1; + return 0; +} --=20 2.48.1