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Wed, 14 Jun 2023 05:23:16 -0500 From: Swapnil Sapkal To: , , , CC: , , , , , , , , , , , Swapnil Sapkal Subject: [PATCH 1/2] sched/fair: Fix value reported by hot tasks pulled in /proc/schedstat Date: Wed, 14 Jun 2023 10:22:23 +0000 Message-ID: <20230614102224.12555-2-swapnil.sapkal@amd.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230614102224.12555-1-swapnil.sapkal@amd.com> References: <20230614102224.12555-1-swapnil.sapkal@amd.com> MIME-Version: 1.0 X-Originating-IP: [10.180.168.240] X-ClientProxiedBy: SATLEXMB04.amd.com (10.181.40.145) To SATLEXMB04.amd.com (10.181.40.145) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CY4PEPF0000EE3F:EE_|SA3PR12MB9106:EE_ X-MS-Office365-Filtering-Correlation-Id: d35ed990-bf44-456a-38e2-08db6cc15f0c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: FtLUoLG0trDqSRv0z+Z2sxxxIedH+vLkDc0gAd5hW24h5Wig3YboCRutc4mualdqZuDqGGg65DnSQBxid2IfaId1QNqEL5TUPatX/XcwzxaFqLlFEutA8R68KnTSCRhrxeghCQlpXFLpEJdWYUsddhyxbcTdXfa3RBQIC1O4bjFsaVpQahUiVqTvh4sYgBCDLTJLKhxc3ugmNsYn61BB9IeaNPoJcd/vv2Xk7PYnRwYpoArYC4j24ekdGrMLxeiojF+oj96gPY+Qb85ILOKk5O+i0kFC/EhUs1Un4GCZv3MVzDoVWOohJfxMGA5EeEhuMaLewvsItRDEIvFZPk0MHApzQLIBFkduqs2lDB5lLM41ycFsVsxY54zrFJJkLnyxbGyUNm7Iq81efsLZcevylylDo/Uf8GJLZMjYqXU9DM7lBftQgo1fwqOQYcUSRMlloKdqv97WB7/VTdZgp4Ps/iq647m566cBipBBXjLd6vLYU9u4J6RbMvC0FYhHPLEERbk9S9zZC92zNboo8zybr9ncm0EaNJlhgT4696x3QIs6GYNP4CGNi8m3SvEy04wBcfOEeLFxIXURAKFGzzPBfzRx7GVuM8O3a46XMX50yA0YKDNQ3HQGN2kBo+ywn6xeefdc5PeFvQDg5zxnUwaZbtrwZ6HLU5sLmtJdOSnbJU5676ndm0powZIrSZcLc0nYLGxG4n12S/gRYjV/VKQs050bXZlvQhCWoac0qrxuWB9sRNwn9JBqQelOLAicvT8f X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:CAL;SFV:NSPM;H:SATLEXMB04.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230028)(4636009)(376002)(346002)(136003)(396003)(39860400002)(451199021)(46966006)(40470700004)(36840700001)(26005)(478600001)(16526019)(36756003)(1076003)(186003)(40480700001)(6666004)(40460700003)(7696005)(2906002)(316002)(41300700001)(44832011)(86362001)(356005)(81166007)(82310400005)(8676002)(5660300002)(82740400003)(8936002)(7416002)(110136005)(426003)(336012)(54906003)(47076005)(83380400001)(2616005)(70586007)(70206006)(4326008)(36860700001)(36900700001);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 Jun 2023 10:23:18.1087 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: d35ed990-bf44-456a-38e2-08db6cc15f0c X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: CY4PEPF0000EE3F.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA3PR12MB9106 X-Spam-Status: No, score=-1.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FORGED_SPF_HELO, RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE, T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1768673732268878242?= X-GMAIL-MSGID: =?utf-8?q?1768673732268878242?= In /proc/schedstat, lb_hot_gained reports the number hot tasks pulled during load balance. This value is incremented in can_migrate_task() if the task is migratable and hot. After incrementing the value, load balancer can still decide not to migrate this task leading to wrong accounting. Fix this by incrementing stats when hot tasks are detached. This issue only exits in detach_tasks() where we can decide to not migrate hot task even if it is migratable. However, in detach_one_task(), we migrate it unconditionally. Fixes: d31980846f96 ("sched: Move up affinity check to mitigate useless redoing overhead") Reported-by: Gautham R. Shenoy Signed-off-by: Swapnil Sapkal --- kernel/sched/fair.c | 47 +++++++++++++++++++++++++++++---------------- 1 file changed, 30 insertions(+), 17 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 373ff5f55884..9a8e5dcbe7e6 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -8507,9 +8507,9 @@ static inline int migrate_degrades_locality(struct task_struct *p, * can_migrate_task - may task p from runqueue rq be migrated to this_cpu? */ static -int can_migrate_task(struct task_struct *p, struct lb_env *env) +int can_migrate_task(struct task_struct *p, struct lb_env *env, int *tsk_cache_hot) { - int tsk_cache_hot; + int degrades_locality; lockdep_assert_rq_held(env->src_rq); @@ -8578,18 +8578,19 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env) if (env->flags & LBF_ACTIVE_LB) return 1; - tsk_cache_hot = migrate_degrades_locality(p, env); - if (tsk_cache_hot == -1) - tsk_cache_hot = task_hot(p, env); + degrades_locality = migrate_degrades_locality(p, env); + if (degrades_locality == -1) + *tsk_cache_hot = task_hot(p, env); + else + *tsk_cache_hot = degrades_locality; - if (tsk_cache_hot <= 0 || - env->sd->nr_balance_failed > env->sd->cache_nice_tries) { - if (tsk_cache_hot == 1) { - schedstat_inc(env->sd->lb_hot_gained[env->idle]); - schedstat_inc(p->stats.nr_forced_migrations); - } + /* + * Can migrate a hot task only after the attempts to reach balance + * without the task have exceeded the cache_nice_tries threshold. + */ + if (!(*tsk_cache_hot) || + env->sd->nr_balance_failed > env->sd->cache_nice_tries) return 1; - } schedstat_inc(p->stats.nr_failed_migrations_hot); return 0; @@ -8598,10 +8599,15 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env) /* * detach_task() -- detach the task for the migration specified in env */ -static void detach_task(struct task_struct *p, struct lb_env *env) +static void detach_task(struct task_struct *p, struct lb_env *env, int tsk_cache_hot) { lockdep_assert_rq_held(env->src_rq); + if (tsk_cache_hot == 1) { + schedstat_inc(env->sd->lb_hot_gained[env->idle]); + schedstat_inc(p->stats.nr_forced_migrations); + } + deactivate_task(env->src_rq, p, DEQUEUE_NOCLOCK); set_task_cpu(p, env->dst_cpu); } @@ -8620,10 +8626,12 @@ static struct task_struct *detach_one_task(struct lb_env *env) list_for_each_entry_reverse(p, &env->src_rq->cfs_tasks, se.group_node) { - if (!can_migrate_task(p, env)) + int tsk_cache_hot = 0; + + if (!can_migrate_task(p, env, &tsk_cache_hot)) continue; - detach_task(p, env); + detach_task(p, env, tsk_cache_hot); /* * Right now, this is only the second place where @@ -8665,6 +8673,8 @@ static int detach_tasks(struct lb_env *env) return 0; while (!list_empty(tasks)) { + int tsk_cache_hot = 0; + /* * We don't want to steal all, otherwise we may be treated likewise, * which could at worst lead to a livelock crash. @@ -8690,7 +8700,7 @@ static int detach_tasks(struct lb_env *env) p = list_last_entry(tasks, struct task_struct, se.group_node); - if (!can_migrate_task(p, env)) + if (!can_migrate_task(p, env, &tsk_cache_hot)) goto next; switch (env->migration_type) { @@ -8742,7 +8752,7 @@ static int detach_tasks(struct lb_env *env) break; } - detach_task(p, env); + detach_task(p, env, tsk_cache_hot); list_add(&p->se.group_node, &env->tasks); detached++; @@ -8766,6 +8776,9 @@ static int detach_tasks(struct lb_env *env) continue; next: + if (tsk_cache_hot == 1) + schedstat_inc(p->stats.nr_failed_migrations_hot); + list_move(&p->se.group_node, tasks); } From patchwork Wed Jun 14 10:22:24 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Swapnil Sapkal X-Patchwork-Id: 107870 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:a59:994d:0:b0:3d9:f83d:47d9 with SMTP id k13csp1139228vqr; Wed, 14 Jun 2023 03:32:17 -0700 (PDT) X-Google-Smtp-Source: ACHHUZ4K8LHJiuJW2Elu812kRSbKG3HlSXqqACMXw17W/UsToBx/yVtrK7oHaxWDsdAvEuJ3scpE X-Received: by 2002:a05:620a:2b0f:b0:75d:8731:4e9f with SMTP id do15-20020a05620a2b0f00b0075d87314e9fmr14053946qkb.69.1686738737600; 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Wed, 14 Jun 2023 05:23:39 -0500 From: Swapnil Sapkal To: , , , CC: , , , , , , , , , , , Swapnil Sapkal Subject: [PATCH 2/2] sched/fair: Cleanup in migrate_degrades_locality() to improve readability Date: Wed, 14 Jun 2023 10:22:24 +0000 Message-ID: <20230614102224.12555-3-swapnil.sapkal@amd.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230614102224.12555-1-swapnil.sapkal@amd.com> References: <20230614102224.12555-1-swapnil.sapkal@amd.com> MIME-Version: 1.0 X-Originating-IP: [10.180.168.240] X-ClientProxiedBy: SATLEXMB04.amd.com (10.181.40.145) To SATLEXMB04.amd.com (10.181.40.145) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CY4PEPF0000EE3A:EE_|SJ2PR12MB8739:EE_ X-MS-Office365-Filtering-Correlation-Id: 41445e9b-1dd1-4537-a9a6-08db6cc16c83 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:CAL;SFV:NSPM;H:SATLEXMB04.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230028)(4636009)(396003)(39860400002)(376002)(346002)(136003)(451199021)(46966006)(36840700001)(40470700004)(336012)(40460700003)(2906002)(478600001)(426003)(2616005)(82310400005)(1076003)(26005)(36860700001)(47076005)(81166007)(86362001)(356005)(83380400001)(16526019)(82740400003)(186003)(7696005)(6666004)(70206006)(40480700001)(110136005)(7416002)(36756003)(4326008)(70586007)(5660300002)(44832011)(8676002)(8936002)(316002)(54906003)(41300700001)(36900700001);DIR:OUT;SFP:1101; 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Handle this return values with enum to improve the readability. Signed-off-by: Swapnil Sapkal --- kernel/sched/fair.c | 69 +++++++++++++++++++++++++++++---------------- 1 file changed, 44 insertions(+), 25 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 9a8e5dcbe7e6..06813ce5356e 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -8443,45 +8443,52 @@ static int task_hot(struct task_struct *p, struct lb_env *env) return delta < (s64)sysctl_sched_migration_cost; } +enum migration_impact { + /* if task migration is not affected by locality */ + no_change = -1, + + /* if task migration improves locality i.e migration preferred */ + improves_locality = 0, + + /* if task migration degrades locality */ + degrades_locality = 1 +}; + #ifdef CONFIG_NUMA_BALANCING -/* - * Returns 1, if task migration degrades locality - * Returns 0, if task migration improves locality i.e migration preferred. - * Returns -1, if task migration is not affected by locality. - */ -static int migrate_degrades_locality(struct task_struct *p, struct lb_env *env) +static enum migration_impact +migrate_degrades_locality(struct task_struct *p, struct lb_env *env) { struct numa_group *numa_group = rcu_dereference(p->numa_group); unsigned long src_weight, dst_weight; int src_nid, dst_nid, dist; if (!static_branch_likely(&sched_numa_balancing)) - return -1; + return no_change; if (!p->numa_faults || !(env->sd->flags & SD_NUMA)) - return -1; + return no_change; src_nid = cpu_to_node(env->src_cpu); dst_nid = cpu_to_node(env->dst_cpu); if (src_nid == dst_nid) - return -1; + return no_change; /* Migrating away from the preferred node is always bad. */ if (src_nid == p->numa_preferred_nid) { if (env->src_rq->nr_running > env->src_rq->nr_preferred_running) - return 1; + return degrades_locality; else - return -1; + return no_change; } /* Encourage migration to the preferred node. */ if (dst_nid == p->numa_preferred_nid) - return 0; + return improves_locality; /* Leaving a core idle is often worse than degrading locality. */ if (env->idle == CPU_IDLE) - return -1; + return no_change; dist = node_distance(src_nid, dst_nid); if (numa_group) { @@ -8492,14 +8499,14 @@ static int migrate_degrades_locality(struct task_struct *p, struct lb_env *env) dst_weight = task_weight(p, dst_nid, dist); } - return dst_weight < src_weight; + return (dst_weight < src_weight) ? degrades_locality : improves_locality; } #else -static inline int migrate_degrades_locality(struct task_struct *p, - struct lb_env *env) +static inline enum migration_impact +migrate_degrades_locality(struct task_struct *p, struct lb_env *env) { - return -1; + return no_change; } #endif @@ -8509,7 +8516,7 @@ static inline int migrate_degrades_locality(struct task_struct *p, static int can_migrate_task(struct task_struct *p, struct lb_env *env, int *tsk_cache_hot) { - int degrades_locality; + enum migration_impact migration_impact; lockdep_assert_rq_held(env->src_rq); @@ -8578,18 +8585,30 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env, int *tsk_cache_h if (env->flags & LBF_ACTIVE_LB) return 1; - degrades_locality = migrate_degrades_locality(p, env); - if (degrades_locality == -1) + migration_impact = migrate_degrades_locality(p, env); + + switch (migration_impact) { + case no_change: *tsk_cache_hot = task_hot(p, env); - else - *tsk_cache_hot = degrades_locality; + break; + + case degrades_locality: + *tsk_cache_hot = 1; + break; + + case improves_locality: + *tsk_cache_hot = 0; + break; + } + + if (!(*tsk_cache_hot)) + return 1; /* - * Can migrate a hot task only after the attempts to reach balance + * Can migrate a task only after the attempts to reach balance * without the task have exceeded the cache_nice_tries threshold. */ - if (!(*tsk_cache_hot) || - env->sd->nr_balance_failed > env->sd->cache_nice_tries) + if (env->sd->nr_balance_failed > env->sd->cache_nice_tries) return 1; schedstat_inc(p->stats.nr_failed_migrations_hot);