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Patch "kernek/fork.c: allocate idle task for a CPU always on its local node" has been added to the 4.4-stable tree

PATCH [email protected] 1 participant 1 message Mar 22, 2017

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This is a note to let you know that I've just added the patch titled

kernek/fork.c: allocate idle task for a CPU always on its local node

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kernek-fork.c-allocate-idle-task-for-a-cpu-always-on-its-local-node.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From 725fc629ff2545b061407305ae51016c9f928fce Mon Sep 17 00:00:00 2001

From: Andi Kleen <[email protected]>
Date: Mon, 23 May 2016 16:24:05 -0700
Subject: kernek/fork.c: allocate idle task for a CPU always on its local node

From: Andi Kleen <[email protected]>

commit 725fc629ff2545b061407305ae51016c9f928fce upstream.

Linux preallocates the task structs of the idle tasks for all possible CPUs. This currently means they all end up on node 0. This also implies that the cache line of MWAIT, which is around the flags field in the task struct, are all located in node 0.

We see a noticeable performance improvement on Knights Landing CPUs when the cache lines used for MWAIT are located in the local nodes of the CPUs using them. I would expect this to give a (likely slight) improvement on other systems too.

The patch implements placing the idle task in the node of its CPUs, by passing the right target node to copy_process()

[[email protected]: use NUMA_NO_NODE, not a bare -1]
Link http://lkml.kernel.org/r/[email protected] open here
Signed-off-by Andi Kleen <[email protected]>
Cc Thomas Gleixner <[email protected]>
Signed-off-by Andrew Morton <[email protected]>
Signed-off-by Linus Torvalds <[email protected]>
Cc Sumit Semwal <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 kernel/fork.c |   15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)
kernel/fork.c +9 -6
@@ -331,13 +331,14 @@ void set_task_stack_end_magic(struct tas
 	*stackend = STACK_END_MAGIC;	/* for overflow detection */
 }
 
-static struct task_struct *dup_task_struct(struct task_struct *orig)
+static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 {
 	struct task_struct *tsk;
 	struct thread_info *ti;
-	int node = tsk_fork_get_node(orig);
 	int err;
 
+	if (node == NUMA_NO_NODE)
+		node = tsk_fork_get_node(orig);
 	tsk = alloc_task_struct_node(node);
 	if (!tsk)
 		return NULL;

@@ -1270,7 +1271,8 @@ static struct task_struct *copy_process(
 					int __user *child_tidptr,
 					struct pid *pid,
 					int trace,
-					unsigned long tls)
+					unsigned long tls,
+					int node)
 {
 	int retval;
 	struct task_struct *p;

@@ -1323,7 +1325,7 @@ static struct task_struct *copy_process(
 		goto fork_out;
 
 	retval = -ENOMEM;
-	p = dup_task_struct(current);
+	p = dup_task_struct(current, node);
 	if (!p)
 		goto fork_out;
 

@@ -1699,7 +1701,8 @@ static inline void init_idle_pids(struct
 struct task_struct *fork_idle(int cpu)
 {
 	struct task_struct *task;
-	task = copy_process(CLONE_VM, 0, 0, NULL, &init_struct_pid, 0, 0);
+	task = copy_process(CLONE_VM, 0, 0, NULL, &init_struct_pid, 0, 0,
+			    cpu_to_node(cpu));
 	if (!IS_ERR(task)) {
 		init_idle_pids(task->pids);
 		init_idle(task, cpu);

@@ -1744,7 +1747,7 @@ long _do_fork(unsigned long clone_flags,
 	}
 
 	p = copy_process(clone_flags, stack_start, stack_size,
-			 child_tidptr, NULL, trace, tls);
+			 child_tidptr, NULL, trace, tls, NUMA_NO_NODE);
 	/*
 	 * Do this prior waking up the new thread - the thread pointer
 	 * might get invalid after that point, if the thread exits quickly.

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/kernek-fork.c-allocate-idle-task-for-a-cpu-always-on-its-local-node.patch