[IA64] Use bitmaps for efficient context allocation/free

Corrects the very inefficent method of finding free context_ids in
get_mmu_context().  Instead of walking the task_list of all processes,
2 bitmaps are used to efficently store and lookup state, inuse and
needs flushing. The entire rid address space is now used before calling
wrap_mmu_context and global tlb flushing.

Special thanks to Ken and Rohit for their review and modifications in
using a bit flushmap.

Signed-off-by: Peter Keilty <peter.keilty@hp.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

4 files changed, 44 insertions, 33 deletions

diff --git a/arch/ia64/kernel/setup.c b/arch/ia64/kernel/setup.c
index fc56ca2da358..c9388a92cf4a 100644
--- a/arch/ia64/kernel/setup.c
+++ b/arch/ia64/kernel/setup.c
@@ -454,6 +454,7 @@ setup_arch (char **cmdline_p)
 #endif
 
         cpu_init();     /* initialize the bootstrap CPU */
+        mmu_context_init();     /* initialize context_id bitmap */
 
 #ifdef CONFIG_ACPI
         acpi_boot_init();
diff --git a/arch/ia64/mm/tlb.c b/arch/ia64/mm/tlb.c
index c79a9b96d02b..39628fca274c 100644
--- a/arch/ia64/mm/tlb.c
+++ b/arch/ia64/mm/tlb.c
@@ -8,6 +8,8 @@
  *              Modified RID allocation for SMP
  *          Goutham Rao <goutham.rao@intel.com>
  *              IPI based ptc implementation and A-step IPI implementation.
+ * Rohit Seth <rohit.seth@intel.com>
+ * Ken Chen <kenneth.w.chen@intel.com>
  */
 #include <linux/config.h>
 #include <linux/module.h>
@@ -16,12 +18,14 @@
 #include <linux/sched.h>
 #include <linux/smp.h>
 #include <linux/mm.h>
+#include <linux/bootmem.h>
 
 #include <asm/delay.h>
 #include <asm/mmu_context.h>
 #include <asm/pgalloc.h>
 #include <asm/pal.h>
 #include <asm/tlbflush.h>
+#include <asm/dma.h>
 
 static struct {
         unsigned long mask;     /* mask of supported purge page-sizes */
@@ -31,49 +35,43 @@ static struct {
 struct ia64_ctx ia64_ctx = {
         .lock =         SPIN_LOCK_UNLOCKED,
         .next =         1,
-        .limit =        (1 << 15) - 1,          /* start out with the safe (architected) limit */
         .max_ctx =      ~0U
 };
 
 DEFINE_PER_CPU(u8, ia64_need_tlb_flush);
 
 /*
+ * Initializes the ia64_ctx.bitmap array based on max_ctx+1.
+ * Called after cpu_init() has setup ia64_ctx.max_ctx based on
+ * maximum RID that is supported by boot CPU.
+ */
+void __init
+mmu_context_init (void)
+{
+        ia64_ctx.bitmap = alloc_bootmem((ia64_ctx.max_ctx+1)>>3);
+        ia64_ctx.flushmap = alloc_bootmem((ia64_ctx.max_ctx+1)>>3);
+}
+
+/*
  * Acquire the ia64_ctx.lock before calling this function!
  */
 void
 wrap_mmu_context (struct mm_struct *mm)
 {
-        unsigned long tsk_context, max_ctx = ia64_ctx.max_ctx;
-        struct task_struct *tsk;
         int i;
+        unsigned long flush_bit;
 
-        if (ia64_ctx.next > max_ctx)
-                ia64_ctx.next = 300;    /* skip daemons */
-        ia64_ctx.limit = max_ctx + 1;
-
-        /*
-         * Scan all the task's mm->context and set proper safe range
-         */
-
-        read_lock(&tasklist_lock);
-  repeat:
-        for_each_process(tsk) {
-                if (!tsk->mm)
-                        continue;
-                tsk_context = tsk->mm->context;
-                if (tsk_context == ia64_ctx.next) {
-                        if (++ia64_ctx.next >= ia64_ctx.limit) {
-                                /* empty range: reset the range limit and start over */
-                                if (ia64_ctx.next > max_ctx)
-                                        ia64_ctx.next = 300;
-                                ia64_ctx.limit = max_ctx + 1;
-                                goto repeat;
-                        }
-                }
-                if ((tsk_context > ia64_ctx.next) && (tsk_context < ia64_ctx.limit))
-                        ia64_ctx.limit = tsk_context;
+        for (i=0; i <= ia64_ctx.max_ctx / BITS_PER_LONG; i++) {
+                flush_bit = xchg(&ia64_ctx.flushmap[i], 0);
+                ia64_ctx.bitmap[i] ^= flush_bit;
         }
-        read_unlock(&tasklist_lock);
+ 
+        /* use offset at 300 to skip daemons */
+        ia64_ctx.next = find_next_zero_bit(ia64_ctx.bitmap,
+                                ia64_ctx.max_ctx, 300);
+        ia64_ctx.limit = find_next_bit(ia64_ctx.bitmap,
+                                ia64_ctx.max_ctx, ia64_ctx.next);
+
         /* can't call flush_tlb_all() here because of race condition with O(1) scheduler [EF] */
         {
                 int cpu = get_cpu(); /* prevent preemption/migration */
diff --git a/include/asm-ia64/mmu_context.h b/include/asm-ia64/mmu_context.h
index 8d6e72f7b08e..8d9b30b5f7d4 100644
--- a/include/asm-ia64/mmu_context.h
+++ b/include/asm-ia64/mmu_context.h
@@ -32,13 +32,17 @@
 struct ia64_ctx {
         spinlock_t lock;
         unsigned int next;      /* next context number to use */
-        unsigned int limit;     /* next >= limit => must call wrap_mmu_context() */
-        unsigned int max_ctx;   /* max. context value supported by all CPUs */
+        unsigned int limit;     /* available free range */
+        unsigned int max_ctx;   /* max. context value supported by all CPUs */
+                                /* call wrap_mmu_context when next >= max */
+        unsigned long *bitmap;  /* bitmap size is max_ctx+1 */
+        unsigned long *flushmap;/* pending rid to be flushed */
 };
 
 extern struct ia64_ctx ia64_ctx;
 DECLARE_PER_CPU(u8, ia64_need_tlb_flush);
 
+extern void mmu_context_init (void);
 extern void wrap_mmu_context (struct mm_struct *mm);
 
 static inline void
@@ -83,9 +87,16 @@ get_mmu_context (struct mm_struct *mm)
                         context = mm->context;
                         if (context == 0) {
                                 cpus_clear(mm->cpu_vm_mask);
-                                if (ia64_ctx.next >= ia64_ctx.limit)
-                                        wrap_mmu_context(mm);
+                                if (ia64_ctx.next >= ia64_ctx.limit) {
+                                        ia64_ctx.next = find_next_zero_bit(ia64_ctx.bitmap,
+                                                        ia64_ctx.max_ctx, ia64_ctx.next);
+                                        ia64_ctx.limit = find_next_bit(ia64_ctx.bitmap,
+                                                        ia64_ctx.max_ctx, ia64_ctx.next);
+                                        if (ia64_ctx.next >= ia64_ctx.max_ctx)
+                                                wrap_mmu_context(mm);
+                                }
                                 mm->context = context = ia64_ctx.next++;
+                                __set_bit(context, ia64_ctx.bitmap);
                         }
                 }
                 spin_unlock_irqrestore(&ia64_ctx.lock, flags);
diff --git a/include/asm-ia64/tlbflush.h b/include/asm-ia64/tlbflush.h
index b65c62702724..a35b323bae4c 100644
--- a/include/asm-ia64/tlbflush.h
+++ b/include/asm-ia64/tlbflush.h
@@ -51,6 +51,7 @@ flush_tlb_mm (struct mm_struct *mm)
         if (!mm)
                 return;
 
+        set_bit(mm->context, ia64_ctx.flushmap);
         mm->context = 0;
 
         if (atomic_read(&mm->mm_users) == 0)