5 files changed, 79 insertions, 8 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 6cfd71d06463..6d18ef8071b5 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -458,6 +458,33 @@ config RCU_FANOUT
           Select a specific number if testing RCU itself.
           Take the default if unsure.
 
+config RCU_FANOUT_LEAF
+        int "Tree-based hierarchical RCU leaf-level fanout value"
+        range 2 RCU_FANOUT if 64BIT
+        range 2 RCU_FANOUT if !64BIT
+        depends on TREE_RCU || TREE_PREEMPT_RCU
+        default 16
+        help
+          This option controls the leaf-level fanout of hierarchical
+          implementations of RCU, and allows trading off cache misses
+          against lock contention.  Systems that synchronize their
+          scheduling-clock interrupts for energy-efficiency reasons will
+          want the default because the smaller leaf-level fanout keeps
+          lock contention levels acceptably low.  Very large systems
+          (hundreds or thousands of CPUs) will instead want to set this
+          value to the maximum value possible in order to reduce the
+          number of cache misses incurred during RCU's grace-period
+          initialization.  These systems tend to run CPU-bound, and thus
+          are not helped by synchronized interrupts, and thus tend to
+          skew them, which reduces lock contention enough that large
+          leaf-level fanouts work well.
+
+          Select a specific number if testing RCU itself.
+
+          Select the maximum permissible value for large systems.
+
+          Take the default if unsure.
+
 config RCU_FANOUT_EXACT
         bool "Disable tree-based hierarchical RCU auto-balancing"
         depends on TREE_RCU || TREE_PREEMPT_RCU
@@ -515,10 +542,25 @@ config RCU_BOOST_PRIO
         depends on RCU_BOOST
         default 1
         help
-          This option specifies the real-time priority to which preempted
-          RCU readers are to be boosted.  If you are working with CPU-bound
-          real-time applications, you should specify a priority higher then
-          the highest-priority CPU-bound application.
+          This option specifies the real-time priority to which long-term
+          preempted RCU readers are to be boosted.  If you are working
+          with a real-time application that has one or more CPU-bound
+          threads running at a real-time priority level, you should set
+          RCU_BOOST_PRIO to a priority higher then the highest-priority
+          real-time CPU-bound thread.  The default RCU_BOOST_PRIO value
+          of 1 is appropriate in the common case, which is real-time
+          applications that do not have any CPU-bound threads.
+
+          Some real-time applications might not have a single real-time
+          thread that saturates a given CPU, but instead might have
+          multiple real-time threads that, taken together, fully utilize
+          that CPU.  In this case, you should set RCU_BOOST_PRIO to
+          a priority higher than the lowest-priority thread that is
+          conspiring to prevent the CPU from running any non-real-time
+          tasks.  For example, if one thread at priority 10 and another
+          thread at priority 5 are between themselves fully consuming
+          the CPU time on a given CPU, then RCU_BOOST_PRIO should be
+          set to priority 6 or higher.
 
           Specify the real-time priority, or take the default if unsure.
 
diff --git a/init/Makefile b/init/Makefile
index 0bf677aa0872..7bc47ee31c36 100644
--- a/init/Makefile
+++ b/init/Makefile
@@ -10,6 +10,10 @@ obj-$(CONFIG_BLK_DEV_INITRD)   += initramfs.o
 endif
 obj-$(CONFIG_GENERIC_CALIBRATE_DELAY) += calibrate.o
 
+ifneq ($(CONFIG_ARCH_INIT_TASK),y)
+obj-y                          += init_task.o
+endif
+
 mounts-y                        := do_mounts.o
 mounts-$(CONFIG_BLK_DEV_RAM)    += do_mounts_rd.o
 mounts-$(CONFIG_BLK_DEV_INITRD) += do_mounts_initrd.o
diff --git a/init/do_mounts.c b/init/do_mounts.c
index 0e93f92a0345..42b0707c3481 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -472,7 +472,7 @@ void __init change_floppy(char *fmt, ...)
 void __init mount_root(void)
 {
 #ifdef CONFIG_ROOT_NFS
-        if (MAJOR(ROOT_DEV) == UNNAMED_MAJOR) {
+        if (ROOT_DEV == Root_NFS) {
                 if (mount_nfs_root())
                         return;
 
diff --git a/init/init_task.c b/init/init_task.c
new file mode 100644
index 000000000000..8b2f3996b035
--- /dev/null
+++ b/init/init_task.c
@@ -0,0 +1,24 @@
+#include <linux/init_task.h>
+#include <linux/export.h>
+#include <linux/mqueue.h>
+#include <linux/sched.h>
+#include <linux/init.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+
+#include <asm/pgtable.h>
+#include <asm/uaccess.h>
+
+static struct signal_struct init_signals = INIT_SIGNALS(init_signals);
+static struct sighand_struct init_sighand = INIT_SIGHAND(init_sighand);
+
+/* Initial task structure */
+struct task_struct init_task = INIT_TASK(init_task);
+EXPORT_SYMBOL(init_task);
+
+/*
+ * Initial thread structure. Alignment of this is handled by a special
+ * linker map entry.
+ */
+union thread_union init_thread_union __init_task_data =
+        { INIT_THREAD_INFO(init_task) };
diff --git a/init/main.c b/init/main.c
index 92c47c4dbde8..1ca6b32c4828 100644
--- a/init/main.c
+++ b/init/main.c
@@ -560,9 +560,6 @@ asmlinkage void __init start_kernel(void)
         early_boot_irqs_disabled = false;
         local_irq_enable();
 
-        /* Interrupts are enabled now so all GFP allocations are safe. */
-        gfp_allowed_mask = __GFP_BITS_MASK;
-
         kmem_cache_init_late();
 
         /*
@@ -847,6 +844,10 @@ static int __init kernel_init(void * unused)
          * Wait until kthreadd is all set-up.
          */
         wait_for_completion(&kthreadd_done);
+
+        /* Now the scheduler is fully set up and can do blocking allocations */
+        gfp_allowed_mask = __GFP_BITS_MASK;
+
         /*
          * init can allocate pages on any node
          */