From patchwork Fri Sep 8 22:49:15 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Elliot Berman X-Patchwork-Id: 13377884 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 A7A16EEB570 for ; Fri, 8 Sep 2023 22:50:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344334AbjIHWu7 (ORCPT ); Fri, 8 Sep 2023 18:50:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60814 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240516AbjIHWu6 (ORCPT ); Fri, 8 Sep 2023 18:50:58 -0400 Received: from mx0a-0031df01.pphosted.com (mx0a-0031df01.pphosted.com [205.220.168.131]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D634A1FEB; Fri, 8 Sep 2023 15:50:54 -0700 (PDT) Received: from pps.filterd (m0279866.ppops.net [127.0.0.1]) by mx0a-0031df01.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 388Mog7D028246; Fri, 8 Sep 2023 22:50:42 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=quicinc.com; h=from : date : subject : mime-version : content-type : content-transfer-encoding : message-id : references : in-reply-to : to : cc; s=qcppdkim1; bh=Z55Ngw5xTpzSsoj7Y26jds8w0rVV/0ec9ylNE7GINhk=; b=jv9+dO0C6X85KKgNvwfzSt0AaReQaqN4kQ5Zbo7PMgqzTQ1z6EM1dOaClf6o+4SvL1jj 5uETzmBXpV2f7N/aiNopSY/s+aevPrP1IPS4b41nqkaq6IPxWAT5TQ2ge2Ye2rsenxxD 6YV6lh+oZLEKnOYigKE7c9m3JhI15o1TfWjRLcQRHTIb98EgP4KAtX3YOyxEOTi5ex5c xGHsfUAFQJux/SvZ7r/vEfMXmGk92nT/P8LgAFYLT8a+eDhYyQH5EjPsmFOXm0t0Nn2i Rcu88jfMdzA605xuff1uQWVWVoAHcYXG4+wtfHs2kf6V0BfjH4nToz2FkZpn/aNU/geS Nw== Received: from nasanppmta02.qualcomm.com (i-global254.qualcomm.com [199.106.103.254]) by mx0a-0031df01.pphosted.com (PPS) with ESMTPS id 3t023wsj44-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 08 Sep 2023 22:50:42 +0000 Received: from nasanex01b.na.qualcomm.com (nasanex01b.na.qualcomm.com [10.46.141.250]) by NASANPPMTA02.qualcomm.com (8.17.1.5/8.17.1.5) with ESMTPS id 388MofIS010603 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 8 Sep 2023 22:50:41 GMT Received: from hu-eberman-lv.qualcomm.com (10.49.16.6) by nasanex01b.na.qualcomm.com (10.46.141.250) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.36; Fri, 8 Sep 2023 15:50:38 -0700 From: Elliot Berman Date: Fri, 8 Sep 2023 15:49:15 -0700 Subject: [PATCH v4 1/2] sched/core: Remove ifdeffery for saved_state MIME-Version: 1.0 Message-ID: <20230908-avoid-spurious-freezer-wakeups-v4-1-6155aa3dafae@quicinc.com> References: <20230908-avoid-spurious-freezer-wakeups-v4-0-6155aa3dafae@quicinc.com> In-Reply-To: <20230908-avoid-spurious-freezer-wakeups-v4-0-6155aa3dafae@quicinc.com> To: Ingo Molnar , Peter Zijlstra , "Rafael J. Wysocki" , Pavel Machek CC: Thomas Gleixner , , , , , Elliot Berman X-Mailer: b4 0.13-dev X-Originating-IP: [10.49.16.6] X-ClientProxiedBy: nalasex01c.na.qualcomm.com (10.47.97.35) To nasanex01b.na.qualcomm.com (10.46.141.250) X-QCInternal: smtphost X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=5800 signatures=585085 X-Proofpoint-GUID: hzGfnqt_xYlvVJstTZOQcLm5PtEBGO2w X-Proofpoint-ORIG-GUID: hzGfnqt_xYlvVJstTZOQcLm5PtEBGO2w X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.267,Aquarius:18.0.957,Hydra:6.0.601,FMLib:17.11.176.26 definitions=2023-09-08_18,2023-09-05_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 spamscore=0 priorityscore=1501 mlxlogscore=892 mlxscore=0 suspectscore=0 impostorscore=0 lowpriorityscore=0 bulkscore=0 clxscore=1015 adultscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2308100000 definitions=main-2309080209 Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org In preparation for freezer to also use saved_state, remove the CONFIG_PREEMPT_RT compilation guard around saved_state. On the arm64 platform I tested which did not have CONFIG_PREEMPT_RT, there was no statistically significant deviation by applying this patch. Test methodology: perf bench sched message -g 40 -l 40 Signed-off-by: Elliot Berman --- include/linux/sched.h | 2 -- kernel/sched/core.c | 17 +++-------------- 2 files changed, 3 insertions(+), 16 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 609bde814cb0..14194a62294f 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -745,10 +745,8 @@ struct task_struct { #endif unsigned int __state; -#ifdef CONFIG_PREEMPT_RT /* saved state for "spinlock sleepers" */ unsigned int saved_state; -#endif /* * This begins the randomizable portion of task_struct. Only diff --git a/kernel/sched/core.c b/kernel/sched/core.c index c52c2eba7c73..58921ab7442b 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2219,31 +2219,21 @@ int __task_state_match(struct task_struct *p, unsigned int state) if (READ_ONCE(p->__state) & state) return 1; -#ifdef CONFIG_PREEMPT_RT if (READ_ONCE(p->saved_state) & state) return -1; -#endif + return 0; } static __always_inline int task_state_match(struct task_struct *p, unsigned int state) { -#ifdef CONFIG_PREEMPT_RT - int match; - /* * Serialize against current_save_and_set_rtlock_wait_state() and * current_restore_rtlock_saved_state(). */ - raw_spin_lock_irq(&p->pi_lock); - match = __task_state_match(p, state); - raw_spin_unlock_irq(&p->pi_lock); - - return match; -#else + guard(raw_spinlock_irq)(&p->pi_lock); return __task_state_match(p, state); -#endif } /* @@ -4053,7 +4043,6 @@ bool ttwu_state_match(struct task_struct *p, unsigned int state, int *success) *success = !!(match = __task_state_match(p, state)); -#ifdef CONFIG_PREEMPT_RT /* * Saved state preserves the task state across blocking on * an RT lock. If the state matches, set p::saved_state to @@ -4069,7 +4058,7 @@ bool ttwu_state_match(struct task_struct *p, unsigned int state, int *success) */ if (match < 0) p->saved_state = TASK_RUNNING; -#endif + return match > 0; } From patchwork Fri Sep 8 22:49:16 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Elliot Berman X-Patchwork-Id: 13377886 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 D6184EEB57A for ; Fri, 8 Sep 2023 22:51:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344439AbjIHWvD (ORCPT ); Fri, 8 Sep 2023 18:51:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60840 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344415AbjIHWvC (ORCPT ); Fri, 8 Sep 2023 18:51:02 -0400 Received: from mx0b-0031df01.pphosted.com (mx0b-0031df01.pphosted.com [205.220.180.131]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2AD991FEB; Fri, 8 Sep 2023 15:50:57 -0700 (PDT) Received: from pps.filterd (m0279873.ppops.net [127.0.0.1]) by mx0a-0031df01.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 388Mcsiu011303; Fri, 8 Sep 2023 22:50:43 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=quicinc.com; h=from : date : subject : mime-version : content-type : content-transfer-encoding : message-id : references : in-reply-to : to : cc; s=qcppdkim1; bh=bs7FO/jLfKZR5eJqufatrmjM1HtZcwMoltAhdaNuRtM=; b=eTsUP2Kq3Vz6sY/ymnXAsr+NWsnb1z66whmPjz47+pP7CVwLens4WU8ZFRu+cewo2pGs XiD922yjRny2a0lfjB4CC7mNlbj3gnc6mVem7SFUvNCdACwpfsnJU9ncp7L6vQLdspJW fHk1s4fSWff788Ig+wIXo8bJqKz3OkqURD+mc3mvwi9baL/7Vzhs6w2jcOq5hzl+zk+3 L1b0FuPPYDKkl5hybUnXeolkA0qLNSL0DtGbo99jiDoK2OY6NMIeNcXX47Fh+AehfF03 h1wGzrSJL0ZaHvSMIzylUT//KjVP0b52FP2aTzKsxtFUzvnNaFCxN3z8wZ//ZlVOI1SZ QQ== Received: from nasanppmta03.qualcomm.com (i-global254.qualcomm.com [199.106.103.254]) by mx0a-0031df01.pphosted.com (PPS) with ESMTPS id 3synyqawdy-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 08 Sep 2023 22:50:43 +0000 Received: from nasanex01b.na.qualcomm.com (nasanex01b.na.qualcomm.com [10.46.141.250]) by NASANPPMTA03.qualcomm.com (8.17.1.5/8.17.1.5) with ESMTPS id 388MogOS000727 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 8 Sep 2023 22:50:42 GMT Received: from hu-eberman-lv.qualcomm.com (10.49.16.6) by nasanex01b.na.qualcomm.com (10.46.141.250) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.36; Fri, 8 Sep 2023 15:50:39 -0700 From: Elliot Berman Date: Fri, 8 Sep 2023 15:49:16 -0700 Subject: [PATCH v4 2/2] freezer,sched: Use saved_state to reduce some spurious wakeups MIME-Version: 1.0 Message-ID: <20230908-avoid-spurious-freezer-wakeups-v4-2-6155aa3dafae@quicinc.com> References: <20230908-avoid-spurious-freezer-wakeups-v4-0-6155aa3dafae@quicinc.com> In-Reply-To: <20230908-avoid-spurious-freezer-wakeups-v4-0-6155aa3dafae@quicinc.com> To: Ingo Molnar , Peter Zijlstra , "Rafael J. Wysocki" , Pavel Machek CC: Thomas Gleixner , , , , , Elliot Berman , "Prakash Viswalingam" X-Mailer: b4 0.13-dev X-Originating-IP: [10.49.16.6] X-ClientProxiedBy: nalasex01c.na.qualcomm.com (10.47.97.35) To nasanex01b.na.qualcomm.com (10.46.141.250) X-QCInternal: smtphost X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=5800 signatures=585085 X-Proofpoint-ORIG-GUID: Nlq7pfKuwTrAlUz89VQZJs8X7CqY0Dl0 X-Proofpoint-GUID: Nlq7pfKuwTrAlUz89VQZJs8X7CqY0Dl0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.267,Aquarius:18.0.957,Hydra:6.0.601,FMLib:17.11.176.26 definitions=2023-09-08_18,2023-09-05_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 mlxscore=0 spamscore=0 clxscore=1015 malwarescore=0 priorityscore=1501 suspectscore=0 mlxlogscore=999 impostorscore=0 phishscore=0 bulkscore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2308100000 definitions=main-2309080208 Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org After commit f5d39b020809 ("freezer,sched: Rewrite core freezer logic"), tasks that transition directly from TASK_FREEZABLE to TASK_FROZEN are always woken up on the thaw path. Prior to that commit, tasks could ask freezer to consider them "frozen enough" via freezer_do_not_count(). The commit replaced freezer_do_not_count() with a TASK_FREEZABLE state which allows freezer to immediately mark the task as TASK_FROZEN without waking up the task. This is efficient for the suspend path, but on the thaw path, the task is always woken up even if the task didn't need to wake up and goes back to its TASK_(UN)INTERRUPTIBLE state. Although these tasks are capable of handling of the wakeup, we can observe a power/perf impact from the extra wakeup. We observed on Android many tasks wait in the TASK_FREEZABLE state (particularly due to many of them being binder clients). We observed nearly 4x the number of tasks and a corresponding linear increase in latency and power consumption when thawing the system. The latency increased from ~15ms to ~50ms. Avoid the spurious wakeups by saving the state of TASK_FREEZABLE tasks. If the task was running before entering TASK_FROZEN state (__refrigerator()) or if the task received a wake up for the saved state, then the task is woken on thaw. saved_state from PREEMPT_RT locks can be re-used because freezer would not stomp on the rtlock wait flow: TASK_RTLOCK_WAIT isn't considered freezable. Reported-by: Prakash Viswalingam Signed-off-by: Elliot Berman --- kernel/freezer.c | 41 +++++++++++++++++++---------------------- kernel/sched/core.c | 23 ++++++++++++++--------- 2 files changed, 33 insertions(+), 31 deletions(-) diff --git a/kernel/freezer.c b/kernel/freezer.c index 4fad0e6fca64..c450fa8b8b5e 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -71,7 +71,11 @@ bool __refrigerator(bool check_kthr_stop) for (;;) { bool freeze; + raw_spin_lock_irq(¤t->pi_lock); set_current_state(TASK_FROZEN); + /* unstale saved_state so that __thaw_task() will wake us up */ + current->saved_state = TASK_RUNNING; + raw_spin_unlock_irq(¤t->pi_lock); spin_lock_irq(&freezer_lock); freeze = freezing(current) && !(check_kthr_stop && kthread_should_stop()); @@ -129,6 +133,7 @@ static int __set_task_frozen(struct task_struct *p, void *arg) WARN_ON_ONCE(debug_locks && p->lockdep_depth); #endif + p->saved_state = p->__state; WRITE_ONCE(p->__state, TASK_FROZEN); return TASK_FROZEN; } @@ -170,42 +175,34 @@ bool freeze_task(struct task_struct *p) } /* - * The special task states (TASK_STOPPED, TASK_TRACED) keep their canonical - * state in p->jobctl. If either of them got a wakeup that was missed because - * TASK_FROZEN, then their canonical state reflects that and the below will - * refuse to restore the special state and instead issue the wakeup. + * Restore the saved_state before the task entered freezer. For typical task + * in the __refrigerator(), saved_state == TASK_RUNNING so nothing happens + * here. For tasks which were TASK_NORMAL | TASK_FREEZABLE, their initial state + * is restored unless they got an expected wakeup (see ttwu_state_match()). + * Returns 1 if the task state was restored. */ -static int __set_task_special(struct task_struct *p, void *arg) +static int __restore_freezer_state(struct task_struct *p, void *arg) { - unsigned int state = 0; + unsigned int state = p->saved_state; - if (p->jobctl & JOBCTL_TRACED) - state = TASK_TRACED; - - else if (p->jobctl & JOBCTL_STOPPED) - state = TASK_STOPPED; - - if (state) + if (state != TASK_RUNNING) { WRITE_ONCE(p->__state, state); + return 1; + } - return state; + return 0; } void __thaw_task(struct task_struct *p) { - unsigned long flags, flags2; + unsigned long flags; spin_lock_irqsave(&freezer_lock, flags); if (WARN_ON_ONCE(freezing(p))) goto unlock; - if (lock_task_sighand(p, &flags2)) { - /* TASK_FROZEN -> TASK_{STOPPED,TRACED} */ - bool ret = task_call_func(p, __set_task_special, NULL); - unlock_task_sighand(p, &flags2); - if (ret) - goto unlock; - } + if (task_call_func(p, __restore_freezer_state, NULL)) + goto unlock; wake_up_state(p, TASK_FROZEN); unlock: diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 58921ab7442b..12f3c500622a 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2229,8 +2229,8 @@ static __always_inline int task_state_match(struct task_struct *p, unsigned int state) { /* - * Serialize against current_save_and_set_rtlock_wait_state() and - * current_restore_rtlock_saved_state(). + * Serialize against current_save_and_set_rtlock_wait_state(), + * current_restore_rtlock_saved_state(), and __refrigerator(). */ guard(raw_spinlock_irq)(&p->pi_lock); return __task_state_match(p, state); @@ -4023,13 +4023,17 @@ static void ttwu_queue(struct task_struct *p, int cpu, int wake_flags) * The caller holds p::pi_lock if p != current or has preemption * disabled when p == current. * - * The rules of PREEMPT_RT saved_state: + * The rules of saved_state: * * The related locking code always holds p::pi_lock when updating * p::saved_state, which means the code is fully serialized in both cases. * - * The lock wait and lock wakeups happen via TASK_RTLOCK_WAIT. No other - * bits set. This allows to distinguish all wakeup scenarios. + * For PREEMPT_RT, the lock wait and lock wakeups happen via TASK_RTLOCK_WAIT. + * No other bits set. This allows to distinguish all wakeup scenarios. + * + * For FREEZER, the wakeup happens via TASK_FROZEN. No other bits set. This + * allows us to prevent early wakeup of tasks before they can be run on + * asymmetric ISA architectures (eg ARMv9). */ static __always_inline bool ttwu_state_match(struct task_struct *p, unsigned int state, int *success) @@ -4045,10 +4049,11 @@ bool ttwu_state_match(struct task_struct *p, unsigned int state, int *success) /* * Saved state preserves the task state across blocking on - * an RT lock. If the state matches, set p::saved_state to - * TASK_RUNNING, but do not wake the task because it waits - * for a lock wakeup. Also indicate success because from - * the regular waker's point of view this has succeeded. + * an RT lock or TASK_FREEZABLE tasks. If the state matches, + * set p::saved_state to TASK_RUNNING, but do not wake the task + * because it waits for a lock wakeup or __thaw_task(). Also + * indicate success because from the regular waker's point of + * view this has succeeded. * * After acquiring the lock the task will restore p::__state * from p::saved_state which ensures that the regular