Commit dcc17d1b authored by Peter Keilty's avatar Peter Keilty Committed by Tony Luck
Browse files

[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: default avatarPeter Keilty <peter.keilty@hp.com>
Signed-off-by: default avatarTony Luck <tony.luck@intel.com>
parent f2c84c0e

arch/ia64/kernel/setup.c

+1 −0
Original line number Diff line number Diff line
@@ -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();

arch/ia64/mm/tlb.c

+27 −29
Original line number Diff line number Diff line
@@ -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;

	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;

	}

 

	/*

	 * Scan all the task's mm->context and set proper safe range

	 */

	/* 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);



	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;

	}

	read_unlock(&tasklist_lock);

	/* can't call flush_tlb_all() here because of race condition with O(1) scheduler [EF] */

	{

		int cpu = get_cpu(); /* prevent preemption/migration */

include/asm-ia64/mmu_context.h

+15 −4
Original line number Diff line number Diff line
@@ -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 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)

				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);

include/asm-ia64/tlbflush.h

+1 −0
Original line number Diff line number Diff line
@@ -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)

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