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From: Will Deacon <will@kernel.org>
To: linux-arm-kernel@lists.infradead.org
Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
	Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Marc Zyngier <maz@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Morten Rasmussen <morten.rasmussen@arm.com>,
	Qais Yousef <qais.yousef@arm.com>,
	Suren Baghdasaryan <surenb@google.com>,
	Quentin Perret <qperret@google.com>, Tejun Heo <tj@kernel.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Ingo Molnar <mingo@redhat.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	kernel-team@android.com,
	Valentin Schneider <Valentin.Schneider@arm.com>
Subject: [PATCH v9 05/20] sched: Introduce task_cpu_possible_mask() to limit fallback rq selection
Date: Tue,  8 Jun 2021 19:02:58 +0100	[thread overview]
Message-ID: <20210608180313.11502-6-will@kernel.org> (raw)
In-Reply-To: <20210608180313.11502-1-will@kernel.org>

Asymmetric systems may not offer the same level of userspace ISA support
across all CPUs, meaning that some applications cannot be executed by
some CPUs. As a concrete example, upcoming arm64 big.LITTLE designs do
not feature support for 32-bit applications on both clusters.

On such a system, we must take care not to migrate a task to an
unsupported CPU when forcefully moving tasks in select_fallback_rq()
in response to a CPU hot-unplug operation.

Introduce a task_cpu_possible_mask() hook which, given a task argument,
allows an architecture to return a cpumask of CPUs that are capable of
executing that task. The default implementation returns the
cpu_possible_mask, since sane machines do not suffer from per-cpu ISA
limitations that affect scheduling. The new mask is used when selecting
the fallback runqueue as a last resort before forcing a migration to the
first active CPU.

Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 include/linux/mmu_context.h | 14 ++++++++++++++
 kernel/sched/core.c         |  5 ++---
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/include/linux/mmu_context.h b/include/linux/mmu_context.h
index 03dee12d2b61..b9b970f7ab45 100644
--- a/include/linux/mmu_context.h
+++ b/include/linux/mmu_context.h
@@ -14,4 +14,18 @@
 static inline void leave_mm(int cpu) { }
 #endif
 
+/*
+ * CPUs that are capable of running user task @p. Must contain at least one
+ * active CPU. It is assumed that the kernel can run on all CPUs, so calling
+ * this for a kernel thread is pointless.
+ *
+ * By default, we assume a sane, homogeneous system.
+ */
+#ifndef task_cpu_possible_mask
+# define task_cpu_possible_mask(p)	cpu_possible_mask
+# define task_cpu_possible(cpu, p)	true
+#else
+# define task_cpu_possible(cpu, p)	cpumask_test_cpu((cpu), task_cpu_possible_mask(p))
+#endif
+
 #endif
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5226cc26a095..0c1b6f1a6c91 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1814,7 +1814,7 @@ static inline bool is_cpu_allowed(struct task_struct *p, int cpu)
 
 	/* Non kernel threads are not allowed during either online or offline. */
 	if (!(p->flags & PF_KTHREAD))
-		return cpu_active(cpu);
+		return cpu_active(cpu) && task_cpu_possible(cpu, p);
 
 	/* KTHREAD_IS_PER_CPU is always allowed. */
 	if (kthread_is_per_cpu(p))
@@ -2792,10 +2792,9 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
 			 *
 			 * More yuck to audit.
 			 */
-			do_set_cpus_allowed(p, cpu_possible_mask);
+			do_set_cpus_allowed(p, task_cpu_possible_mask(p));
 			state = fail;
 			break;
-
 		case fail:
 			BUG();
 			break;
-- 
2.32.0.rc1.229.g3e70b5a671-goog


WARNING: multiple messages have this Message-ID
From: Will Deacon <will@kernel.org>
To: linux-arm-kernel@lists.infradead.org
Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
	Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Marc Zyngier <maz@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Morten Rasmussen <morten.rasmussen@arm.com>,
	Qais Yousef <qais.yousef@arm.com>,
	Suren Baghdasaryan <surenb@google.com>,
	Quentin Perret <qperret@google.com>, Tejun Heo <tj@kernel.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Ingo Molnar <mingo@redhat.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	kernel-team@android.com,
	Valentin Schneider <Valentin.Schneider@arm.com>
Subject: [PATCH v9 05/20] sched: Introduce task_cpu_possible_mask() to limit fallback rq selection
Date: Tue,  8 Jun 2021 19:02:58 +0100	[thread overview]
Message-ID: <20210608180313.11502-6-will@kernel.org> (raw)
In-Reply-To: <20210608180313.11502-1-will@kernel.org>

Asymmetric systems may not offer the same level of userspace ISA support
across all CPUs, meaning that some applications cannot be executed by
some CPUs. As a concrete example, upcoming arm64 big.LITTLE designs do
not feature support for 32-bit applications on both clusters.

On such a system, we must take care not to migrate a task to an
unsupported CPU when forcefully moving tasks in select_fallback_rq()
in response to a CPU hot-unplug operation.

Introduce a task_cpu_possible_mask() hook which, given a task argument,
allows an architecture to return a cpumask of CPUs that are capable of
executing that task. The default implementation returns the
cpu_possible_mask, since sane machines do not suffer from per-cpu ISA
limitations that affect scheduling. The new mask is used when selecting
the fallback runqueue as a last resort before forcing a migration to the
first active CPU.

Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 include/linux/mmu_context.h | 14 ++++++++++++++
 kernel/sched/core.c         |  5 ++---
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/include/linux/mmu_context.h b/include/linux/mmu_context.h
index 03dee12d2b61..b9b970f7ab45 100644
--- a/include/linux/mmu_context.h
+++ b/include/linux/mmu_context.h
@@ -14,4 +14,18 @@
 static inline void leave_mm(int cpu) { }
 #endif
 
+/*
+ * CPUs that are capable of running user task @p. Must contain at least one
+ * active CPU. It is assumed that the kernel can run on all CPUs, so calling
+ * this for a kernel thread is pointless.
+ *
+ * By default, we assume a sane, homogeneous system.
+ */
+#ifndef task_cpu_possible_mask
+# define task_cpu_possible_mask(p)	cpu_possible_mask
+# define task_cpu_possible(cpu, p)	true
+#else
+# define task_cpu_possible(cpu, p)	cpumask_test_cpu((cpu), task_cpu_possible_mask(p))
+#endif
+
 #endif
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5226cc26a095..0c1b6f1a6c91 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1814,7 +1814,7 @@ static inline bool is_cpu_allowed(struct task_struct *p, int cpu)
 
 	/* Non kernel threads are not allowed during either online or offline. */
 	if (!(p->flags & PF_KTHREAD))
-		return cpu_active(cpu);
+		return cpu_active(cpu) && task_cpu_possible(cpu, p);
 
 	/* KTHREAD_IS_PER_CPU is always allowed. */
 	if (kthread_is_per_cpu(p))
@@ -2792,10 +2792,9 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
 			 *
 			 * More yuck to audit.
 			 */
-			do_set_cpus_allowed(p, cpu_possible_mask);
+			do_set_cpus_allowed(p, task_cpu_possible_mask(p));
 			state = fail;
 			break;
-
 		case fail:
 			BUG();
 			break;
-- 
2.32.0.rc1.229.g3e70b5a671-goog


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  parent reply	other threads:[~2021-06-08 18:03 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-08 18:02 [PATCH v9 00/20] Add support for 32-bit tasks on asymmetric AArch32 systems Will Deacon
2021-06-08 18:02 ` Will Deacon
2021-06-08 18:02 ` [PATCH v9 01/20] arm64: cpuinfo: Split AArch32 registers out into a separate struct Will Deacon
2021-06-08 18:02   ` Will Deacon
2021-06-08 18:02 ` [PATCH v9 02/20] arm64: Allow mismatched 32-bit EL0 support Will Deacon
2021-06-08 18:02   ` Will Deacon
2021-06-08 18:02 ` [PATCH v9 03/20] KVM: arm64: Kill 32-bit vCPUs on systems with mismatched " Will Deacon
2021-06-08 18:02   ` Will Deacon
2021-06-08 18:02 ` [PATCH v9 04/20] arm64: Kill 32-bit applications scheduled on 64-bit-only CPUs Will Deacon
2021-06-08 18:02   ` Will Deacon
2021-06-08 18:02 ` Will Deacon [this message]
2021-06-08 18:02   ` [PATCH v9 05/20] sched: Introduce task_cpu_possible_mask() to limit fallback rq selection Will Deacon
2021-06-08 18:02 ` [PATCH v9 06/20] cpuset: Don't use the cpu_possible_mask as a last resort for cgroup v1 Will Deacon
2021-06-08 18:02   ` Will Deacon
2021-06-10 12:59   ` Valentin Schneider
2021-06-10 12:59     ` Valentin Schneider
2021-06-08 18:03 ` [PATCH v9 07/20] cpuset: Honour task_cpu_possible_mask() in guarantee_online_cpus() Will Deacon
2021-06-08 18:03   ` Will Deacon
2021-06-08 18:03 ` [PATCH v9 08/20] cpuset: Cleanup cpuset_cpus_allowed_fallback() use in select_fallback_rq() Will Deacon
2021-06-08 18:03   ` Will Deacon
2021-06-10 12:59   ` Valentin Schneider
2021-06-10 12:59     ` Valentin Schneider
2021-06-08 18:03 ` [PATCH v9 09/20] sched: Reject CPU affinity changes based on task_cpu_possible_mask() Will Deacon
2021-06-08 18:03   ` Will Deacon
2021-06-08 18:03 ` [PATCH v9 10/20] sched: Introduce task_struct::user_cpus_ptr to track requested affinity Will Deacon
2021-06-08 18:03   ` Will Deacon
2021-06-08 18:03 ` [PATCH v9 11/20] sched: Split the guts of sched_setaffinity() into a helper function Will Deacon
2021-06-08 18:03   ` Will Deacon
2021-06-08 18:03 ` [PATCH v9 12/20] sched: Allow task CPU affinity to be restricted on asymmetric systems Will Deacon
2021-06-08 18:03   ` Will Deacon
2021-06-10 13:00   ` Valentin Schneider
2021-06-10 13:00     ` Valentin Schneider
2021-06-08 18:03 ` [PATCH v9 13/20] sched: Introduce dl_task_check_affinity() to check proposed affinity Will Deacon
2021-06-08 18:03   ` Will Deacon
2021-06-08 18:03 ` [PATCH v9 14/20] arm64: Implement task_cpu_possible_mask() Will Deacon
2021-06-08 18:03   ` Will Deacon
2021-06-08 18:03 ` [PATCH v9 15/20] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0 Will Deacon
2021-06-08 18:03   ` Will Deacon
2021-06-08 18:03 ` [PATCH v9 16/20] arm64: Prevent offlining first CPU with 32-bit EL0 on mismatched system Will Deacon
2021-06-08 18:03   ` Will Deacon
2021-06-08 18:03 ` [PATCH v9 17/20] arm64: Advertise CPUs capable of running 32-bit applications in sysfs Will Deacon
2021-06-08 18:03   ` Will Deacon
2021-06-08 18:03 ` [PATCH v9 18/20] arm64: Hook up cmdline parameter to allow mismatched 32-bit EL0 Will Deacon
2021-06-08 18:03   ` Will Deacon
2021-06-08 18:03 ` [PATCH v9 19/20] arm64: Remove logic to kill 32-bit tasks on 64-bit-only cores Will Deacon
2021-06-08 18:03   ` Will Deacon
2021-06-08 18:03 ` [PATCH v9 20/20] Documentation: arm64: describe asymmetric 32-bit support Will Deacon
2021-06-08 18:03   ` Will Deacon
2021-06-11 16:15 ` [PATCH v9 00/20] Add support for 32-bit tasks on asymmetric AArch32 systems Will Deacon
2021-06-11 16:15   ` Will Deacon

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