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Subject[PATCH 1/5] x86: Move fork_idle from wq and idle caching to common code
Date
As a part of cleanup suggested by Ingo here

* move smpboot wq stuff to common code.
* move idle task caching to common code and use the existing percpu
idle_task() as cache, instead of another percpu var or NR_CPUs array.

These can be shared across archs.

Should not have any functionality impact.

Signed-off-by: Venkatesh Pallipadi <venki@google.com>
---
arch/x86/kernel/smpboot.c | 74 ++++++--------------------------------------
include/linux/sched.h | 1 +
kernel/fork.c | 48 +++++++++++++++++++++++++++++
3 files changed, 59 insertions(+), 64 deletions(-)
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 66d250c..cc714b1 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -75,20 +75,8 @@
/* State of each CPU */
DEFINE_PER_CPU(int, cpu_state) = { 0 };

-/* Store all idle threads, this can be reused instead of creating
-* a new thread. Also avoids complicated thread destroy functionality
-* for idle threads.
-*/
#ifdef CONFIG_HOTPLUG_CPU
/*
- * Needed only for CONFIG_HOTPLUG_CPU because __cpuinitdata is
- * removed after init for !CONFIG_HOTPLUG_CPU.
- */
-static DEFINE_PER_CPU(struct task_struct *, idle_thread_array);
-#define get_idle_for_cpu(x) (per_cpu(idle_thread_array, x))
-#define set_idle_for_cpu(x, p) (per_cpu(idle_thread_array, x) = (p))
-
-/*
* We need this for trampoline_base protection from concurrent accesses when
* off- and onlining cores wildly.
*/
@@ -106,10 +94,6 @@ void cpu_hotplug_driver_unlock(void)

ssize_t arch_cpu_probe(const char *buf, size_t count) { return -1; }
ssize_t arch_cpu_release(const char *buf, size_t count) { return -1; }
-#else
-static struct task_struct *idle_thread_array[NR_CPUS] __cpuinitdata ;
-#define get_idle_for_cpu(x) (idle_thread_array[(x)])
-#define set_idle_for_cpu(x, p) (idle_thread_array[(x)] = (p))
#endif

/* Number of siblings per CPU package */
@@ -634,22 +618,6 @@ wakeup_secondary_cpu_via_init(int phys_apicid, unsigned long start_eip)
return (send_status | accept_status);
}

-struct create_idle {
- struct work_struct work;
- struct task_struct *idle;
- struct completion done;
- int cpu;
-};
-
-static void __cpuinit do_fork_idle(struct work_struct *work)
-{
- struct create_idle *c_idle =
- container_of(work, struct create_idle, work);
-
- c_idle->idle = fork_idle(c_idle->cpu);
- complete(&c_idle->done);
-}
-
/* reduce the number of lines printed when booting a large cpu count system */
static void __cpuinit announce_cpu(int cpu, int apicid)
{
@@ -681,53 +649,32 @@ static int __cpuinit do_boot_cpu(int apicid, int cpu)
unsigned long boot_error = 0;
unsigned long start_ip;
int timeout;
- struct create_idle c_idle = {
- .cpu = cpu,
- .done = COMPLETION_INITIALIZER_ONSTACK(c_idle.done),
- };
-
- INIT_WORK_ONSTACK(&c_idle.work, do_fork_idle);
+ struct task_struct *idle;

alternatives_smp_switch(1);

- c_idle.idle = get_idle_for_cpu(cpu);
-
- /*
- * We can't use kernel_thread since we must avoid to
- * reschedule the child.
- */
- if (c_idle.idle) {
- c_idle.idle->thread.sp = (unsigned long) (((struct pt_regs *)
- (THREAD_SIZE + task_stack_page(c_idle.idle))) - 1);
- init_idle(c_idle.idle, cpu);
- goto do_rest;
- }
-
- schedule_work(&c_idle.work);
- wait_for_completion(&c_idle.done);
-
- if (IS_ERR(c_idle.idle)) {
+ idle = fork_idle_from_wq(cpu);
+ if (IS_ERR(idle)) {
printk("failed fork for CPU %d\n", cpu);
- destroy_work_on_stack(&c_idle.work);
- return PTR_ERR(c_idle.idle);
+ return PTR_ERR(idle);
}

- set_idle_for_cpu(cpu, c_idle.idle);
-do_rest:
- per_cpu(current_task, cpu) = c_idle.idle;
+ idle->thread.sp = (unsigned long) (((struct pt_regs *)
+ (THREAD_SIZE + task_stack_page(idle))) - 1);
+ per_cpu(current_task, cpu) = idle;
#ifdef CONFIG_X86_32
/* Stack for startup_32 can be just as for start_secondary onwards */
irq_ctx_init(cpu);
#else
- clear_tsk_thread_flag(c_idle.idle, TIF_FORK);
+ clear_tsk_thread_flag(idle, TIF_FORK);
initial_gs = per_cpu_offset(cpu);
per_cpu(kernel_stack, cpu) =
- (unsigned long)task_stack_page(c_idle.idle) -
+ (unsigned long)task_stack_page(idle) -
KERNEL_STACK_OFFSET + THREAD_SIZE;
#endif
early_gdt_descr.address = (unsigned long)get_cpu_gdt_table(cpu);
initial_code = (unsigned long)start_secondary;
- stack_start = c_idle.idle->thread.sp;
+ stack_start = idle->thread.sp;

/* start_ip had better be page-aligned! */
start_ip = trampoline_address();
@@ -831,7 +778,6 @@ do_rest:
smpboot_restore_warm_reset_vector();
}

- destroy_work_on_stack(&c_idle.work);
return boot_error;
}

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 7d379a6..357057f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2292,6 +2292,7 @@ extern int do_execve(const char *,
const char __user * const __user *, struct pt_regs *);
extern long do_fork(unsigned long, unsigned long, struct pt_regs *, unsigned long, int __user *, int __user *);
struct task_struct *fork_idle(int);
+struct task_struct *fork_idle_from_wq(int);

extern void set_task_comm(struct task_struct *tsk, char *from);
extern char *get_task_comm(char *to, struct task_struct *tsk);
diff --git a/kernel/fork.c b/kernel/fork.c
index e2cd3e2..8704237 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -67,6 +67,8 @@
#include <linux/oom.h>
#include <linux/khugepaged.h>
#include <linux/signalfd.h>
+#include <linux/workqueue.h>
+#include <linux/sched.h>

#include <asm/pgtable.h>
#include <asm/pgalloc.h>
@@ -1479,6 +1481,52 @@ struct task_struct * __cpuinit fork_idle(int cpu)
return task;
}

+struct create_idle {
+ struct work_struct work;
+ struct task_struct *idle;
+ struct completion done;
+ int cpu;
+};
+
+static void __cpuinit do_fork_idle(struct work_struct *work)
+{
+ struct create_idle *c_idle =
+ container_of(work, struct create_idle, work);
+
+ c_idle->idle = fork_idle(c_idle->cpu);
+ complete(&c_idle->done);
+}
+
+struct task_struct * __cpuinit fork_idle_from_wq(int cpu)
+{
+ struct task_struct *idle = idle_task(cpu);
+ struct create_idle c_idle = {
+ .cpu = cpu,
+ .done = COMPLETION_INITIALIZER_ONSTACK(c_idle.done),
+ };
+
+ /* Reuse stored idle thread when possible instead of creating
+ * a new thread. Also avoids complicated thread destroy functionality
+ * for idle threads.
+ */
+ if (idle) {
+ init_idle(idle, cpu);
+ return idle;
+ }
+
+ /*
+ * We can't use kernel_thread since we must avoid to
+ * reschedule the child.
+ */
+ INIT_WORK_ONSTACK(&c_idle.work, do_fork_idle);
+
+ schedule_work(&c_idle.work);
+ wait_for_completion(&c_idle.done);
+ destroy_work_on_stack(&c_idle.work);
+
+ return c_idle.idle;
+}
+
/*
* Ok, this is the main fork-routine.
*
--
1.7.7.3


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