Re: [patch 00/18] SMP: Boot and CPU hotplug refactoring - Part 1

From: Suresh Siddha
Date: Thu May 03 2012 - 19:39:19 EST

On Thu, 2012-05-03 at 11:41 +0200, Thomas Gleixner wrote:
> On Fri, 20 Apr 2012, Suresh Siddha wrote:
> > Also, do we really need the workqueue/kthreadd based allocation? Just
> > like the percpu areas getting allocated for each possible cpu during
> > boot, shouldn't we extend this to the per-cpu idle threads too? So
> > something like the appended should be ok to?
>
> The idea is correct, there are just a few problems :)
>
> > Signed-off-by: Suresh Siddha <suresh.b.siddha@xxxxxxxxx>
> > ---
> > diff --git a/kernel/cpu.c b/kernel/cpu.c
> > index 05c46ba..a5144ab 100644
> > --- a/kernel/cpu.c
> > +++ b/kernel/cpu.c
> > @@ -303,10 +303,6 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
> >
> > cpu_hotplug_begin();
> >
> > - ret = smpboot_prepare(cpu);
> > - if (ret)
> > - goto out;
> > -
>
> If we failed to allocate an idle_thread for this cpu in smp_init()
> then we unconditionally call __cpu_up() with a NULL pointer. That
> might surprise the arch code :)
>
> Aside of that, we now miss to reinitialize the idle thread. We call
> init_idle() once when we allocate the thread, but not after a cpu
> offline operation. That might leave stuff in weird state.

Second one slipped through and wasn't intentional. Anyways your
modifications look good.

While I am here, noticed that we could do 'node' aware idle task struct
allocations. Appended the patch for this. Thanks.
---

From: Suresh Siddha <suresh.b.siddha@xxxxxxxxx>
Subject: idle: allocate percpu idle taks from the local node

Use the arch specific early_cpu_to_node() to find out the local node for a
given 'cpu' and use that info while allocating memory for that cpu's idle task.

Signed-off-by: Suresh Siddha <suresh.b.siddha@xxxxxxxxx>
---
arch/x86/include/asm/topology.h | 8 +++++---
arch/x86/mm/numa.c | 2 +-
include/asm-generic/topology.h | 4 ++++
include/linux/kthread.h | 9 ++++++++-
kernel/fork.c | 9 ++++++---
kernel/kthread.c | 8 +++-----
6 files changed, 27 insertions(+), 13 deletions(-)

diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
index b9676ae..bdbcee2 100644
--- a/arch/x86/include/asm/topology.h
+++ b/arch/x86/include/asm/topology.h
@@ -57,12 +57,12 @@ DECLARE_EARLY_PER_CPU(int, x86_cpu_to_node_map);
extern int __cpu_to_node(int cpu);
#define cpu_to_node __cpu_to_node

-extern int early_cpu_to_node(int cpu);
+extern int __early_cpu_to_node(int cpu);

#else /* !CONFIG_DEBUG_PER_CPU_MAPS */

/* Same function but used if called before per_cpu areas are setup */
-static inline int early_cpu_to_node(int cpu)
+static inline int __early_cpu_to_node(int cpu)
{
return early_per_cpu(x86_cpu_to_node_map, cpu);
}
@@ -144,7 +144,7 @@ static inline int numa_node_id(void)
*/
#define numa_node_id numa_node_id

-static inline int early_cpu_to_node(int cpu)
+static inline int __early_cpu_to_node(int cpu)
{
return 0;
}
@@ -153,6 +153,8 @@ static inline void setup_node_to_cpumask_map(void) { }

#endif

+#define early_cpu_to_node(cpu) __early_cpu_to_node(cpu)
+
#include <asm-generic/topology.h>

extern const struct cpumask *cpu_coregroup_mask(int cpu);
diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
index 19d3fa0..142738e 100644
--- a/arch/x86/mm/numa.c
+++ b/arch/x86/mm/numa.c
@@ -734,7 +734,7 @@ EXPORT_SYMBOL(__cpu_to_node);
* Same function as cpu_to_node() but used if called before the
* per_cpu areas are setup.
*/
-int early_cpu_to_node(int cpu)
+int __early_cpu_to_node(int cpu)
{
if (early_per_cpu_ptr(x86_cpu_to_node_map))
return early_per_cpu_ptr(x86_cpu_to_node_map)[cpu];
diff --git a/include/asm-generic/topology.h b/include/asm-generic/topology.h
index fc824e2..9ace6da 100644
--- a/include/asm-generic/topology.h
+++ b/include/asm-generic/topology.h
@@ -73,4 +73,8 @@

#endif /* !CONFIG_NUMA || !CONFIG_HAVE_MEMORYLESS_NODES */

+#ifndef early_cpu_to_node
+#define early_cpu_to_node(cpu) ((void)(cpu), -1)
+#endif
+
#endif /* _ASM_GENERIC_TOPOLOGY_H */
diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 0714b24..c1f05e3 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -40,7 +40,7 @@ void *kthread_data(struct task_struct *k);

int kthreadd(void *unused);
extern struct task_struct *kthreadd_task;
-extern int tsk_fork_get_node(struct task_struct *tsk);
+extern int tsk_fork_get_node(struct task_struct *tsk, int idle_tsk);

/*
* Simple work processor based on kthread.
@@ -131,4 +131,11 @@ bool queue_kthread_work(struct kthread_worker *worker,
void flush_kthread_work(struct kthread_work *work);
void flush_kthread_worker(struct kthread_worker *worker);

+static inline void set_fork_pref_node(int node)
+{
+#ifdef CONFIG_NUMA
+ current->pref_node_fork = node;
+#endif
+}
+
#endif /* _LINUX_KTHREAD_H */
diff --git a/kernel/fork.c b/kernel/fork.c
index ca9a384..108d566 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -253,12 +253,13 @@ int __attribute__((weak)) arch_dup_task_struct(struct task_struct *dst,
return 0;
}

-static struct task_struct *dup_task_struct(struct task_struct *orig)
+static struct task_struct *dup_task_struct(struct task_struct *orig,
+ int idle_tsk)
{
struct task_struct *tsk;
struct thread_info *ti;
unsigned long *stackend;
- int node = tsk_fork_get_node(orig);
+ int node = tsk_fork_get_node(orig, idle_tsk);
int err;

prepare_to_copy(orig);
@@ -1165,7 +1166,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
goto fork_out;

retval = -ENOMEM;
- p = dup_task_struct(current);
+ p = dup_task_struct(current, pid == &init_struct_pid);
if (!p)
goto fork_out;

@@ -1531,6 +1532,8 @@ struct task_struct * __cpuinit fork_idle(int cpu)
struct task_struct *task;
struct pt_regs regs;

+ set_fork_pref_node(early_cpu_to_node(cpu));
+
task = copy_process(CLONE_VM, 0, idle_regs(&regs), 0, NULL,
&init_struct_pid, 0);
if (!IS_ERR(task)) {
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 3d3de63..3d74ab1 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -125,10 +125,10 @@ static int kthread(void *_create)
}

/* called from do_fork() to get node information for about to be created task */
-int tsk_fork_get_node(struct task_struct *tsk)
+int tsk_fork_get_node(struct task_struct *tsk, int idle_tsk)
{
#ifdef CONFIG_NUMA
- if (tsk == kthreadd_task)
+ if (tsk == kthreadd_task || idle_tsk)
return tsk->pref_node_fork;
#endif
return numa_node_id();
@@ -138,9 +138,7 @@ static void create_kthread(struct kthread_create_info *create)
{
int pid;

-#ifdef CONFIG_NUMA
- current->pref_node_fork = create->node;
-#endif
+ set_fork_pref_node(create->node);
/* We want our own signal handler (we take no signals by default). */
pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
if (pid < 0) {



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