[PATCH 19/31] sched, numa, mm: Introduce tsk_home_node()

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

[-- Attachment #1: 0019-sched-numa-mm-Introduce-tsk_home_node.patch --]
[-- Type: text/plain, Size: 5539 bytes --]

Introduce the home-node concept for tasks. In order to keep memory
locality we need to have a something to stay local to, we define the
home-node of a task as the node we prefer to allocate memory from and
prefer to execute on.

These are no hard guarantees, merely soft preferences. This allows for
optimal resource usage, we can run a task away from the home-node, the
remote memory hit -- while expensive -- is less expensive than not
running at all, or very little, due to severe cpu overload.

Similarly, we can allocate memory from another node if our home-node
is depleted, again, some memory is better than no memory.

This patch merely introduces the basic infrastructure, all policy
comes later.

NOTE: we introduce the concept of EMBEDDED_NUMA, these are
architectures where the memory access cost doesn't depend on the cpu
but purely on the physical address -- embedded boards with cheap
(slow) and expensive (fast) memory banks.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/sh/mm/Kconfig        |    1 +
 include/linux/init_task.h |    8 ++++++++
 include/linux/sched.h     |   12 ++++++++++++
 init/Kconfig              |   14 ++++++++++++++
 kernel/sched/core.c       |   36 ++++++++++++++++++++++++++++++++++++
 5 files changed, 71 insertions(+)

Index: tip/arch/sh/mm/Kconfig
===================================================================
--- tip.orig/arch/sh/mm/Kconfig
+++ tip/arch/sh/mm/Kconfig
@@ -111,6 +111,7 @@ config VSYSCALL
 config NUMA
 	bool "Non Uniform Memory Access (NUMA) Support"
 	depends on MMU && SYS_SUPPORTS_NUMA && EXPERIMENTAL
+	select EMBEDDED_NUMA
 	default n
 	help
 	  Some SH systems have many various memories scattered around
Index: tip/include/linux/init_task.h
===================================================================
--- tip.orig/include/linux/init_task.h
+++ tip/include/linux/init_task.h
@@ -143,6 +143,13 @@ extern struct task_group root_task_group
 
 #define INIT_TASK_COMM "swapper"
 
+#ifdef CONFIG_SCHED_NUMA
+# define INIT_TASK_NUMA(tsk)						\
+	.node = -1,
+#else
+# define INIT_TASK_NUMA(tsk)
+#endif
+
 /*
  *  INIT_TASK is used to set up the first task table, touch at
  * your own risk!. Base=0, limit=0x1fffff (=2MB)
@@ -210,6 +217,7 @@ extern struct task_group root_task_group
 	INIT_TRACE_RECURSION						\
 	INIT_TASK_RCU_PREEMPT(tsk)					\
 	INIT_CPUSET_SEQ							\
+	INIT_TASK_NUMA(tsk)						\
 }
 
 
Index: tip/include/linux/sched.h
===================================================================
--- tip.orig/include/linux/sched.h
+++ tip/include/linux/sched.h
@@ -1479,6 +1479,9 @@ struct task_struct {
 	short il_next;
 	short pref_node_fork;
 #endif
+#ifdef CONFIG_SCHED_NUMA
+	int node;
+#endif
 	struct rcu_head rcu;
 
 	/*
@@ -1553,6 +1556,15 @@ struct task_struct {
 /* Future-safe accessor for struct task_struct's cpus_allowed. */
 #define tsk_cpus_allowed(tsk) (&(tsk)->cpus_allowed)
 
+static inline int tsk_home_node(struct task_struct *p)
+{
+#ifdef CONFIG_SCHED_NUMA
+	return p->node;
+#else
+	return -1;
+#endif
+}
+
 /*
  * Priority of a process goes from 0..MAX_PRIO-1, valid RT
  * priority is 0..MAX_RT_PRIO-1, and SCHED_NORMAL/SCHED_BATCH
Index: tip/init/Kconfig
===================================================================
--- tip.orig/init/Kconfig
+++ tip/init/Kconfig
@@ -696,6 +696,20 @@ config LOG_BUF_SHIFT
 config HAVE_UNSTABLE_SCHED_CLOCK
 	bool
 
+#
+# For architectures that (ab)use NUMA to represent different memory regions
+# all cpu-local but of different latencies, such as SuperH.
+#
+config EMBEDDED_NUMA
+	bool
+
+config SCHED_NUMA
+	bool "Memory placement aware NUMA scheduler"
+	default n
+	depends on SMP && NUMA && MIGRATION && !EMBEDDED_NUMA
+	help
+	  This option adds support for automatic NUMA aware memory/task placement.
+
 menuconfig CGROUPS
 	boolean "Control Group support"
 	depends on EVENTFD
Index: tip/kernel/sched/core.c
===================================================================
--- tip.orig/kernel/sched/core.c
+++ tip/kernel/sched/core.c
@@ -5959,6 +5959,42 @@ static struct sched_domain_topology_leve
 
 static struct sched_domain_topology_level *sched_domain_topology = default_topology;
 
+#ifdef CONFIG_SCHED_NUMA
+
+/*
+ * Requeues a task ensuring its on the right load-balance list so
+ * that it might get migrated to its new home.
+ *
+ * Note that we cannot actively migrate ourselves since our callers
+ * can be from atomic context. We rely on the regular load-balance
+ * mechanisms to move us around -- its all preference anyway.
+ */
+void sched_setnode(struct task_struct *p, int node)
+{
+	unsigned long flags;
+	int on_rq, running;
+	struct rq *rq;
+
+	rq = task_rq_lock(p, &flags);
+	on_rq = p->on_rq;
+	running = task_current(rq, p);
+
+	if (on_rq)
+		dequeue_task(rq, p, 0);
+	if (running)
+		p->sched_class->put_prev_task(rq, p);
+
+	p->node = node;
+
+	if (running)
+		p->sched_class->set_curr_task(rq);
+	if (on_rq)
+		enqueue_task(rq, p, 0);
+	task_rq_unlock(rq, p, &flags);
+}
+
+#endif /* CONFIG_SCHED_NUMA */
+
 #ifdef CONFIG_NUMA
 
 static int sched_domains_numa_levels;


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