Re: [PATCH 6/7] ACPI: Page based coalescing of I/O remappings optimization

[Huang Ying <ying.huang@intel.com>]

Hi, Myron,

On Fri, 2010-10-22 at 04:24 +0800, Myron Stowe wrote:
> This patch optimizes ACPI MMIO remappings by keeping track of the
> remappings on a PAGE_SIZE granularity.
> 
> When an ioremap() occurs, the underlying infrastructure works on a 'page'
> based granularity.  As such, an ioremap() request for 1 byte for example,
> will end up mapping in an entire (PAGE_SIZE) page.  Huang Ying took
> advantage of this in commit 15651291a2f8c11e7e6a42d8bfde7a213ff13262 by
> checking if subsequent ioremap() requests reside within any of the list's
> existing remappings still in place, and if so, incrementing a reference
> count on the existing mapping as opposed to performing another ioremap().
> 
> 
> Signed-off-by: Myron Stowe <myron.stowe@hp.com>
> ---
> 
>  drivers/acpi/osl.c |   62 +++++++++++++++++++++++++++++++++++++++++++---------
>  1 files changed, 51 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
> index 3282689..885e222 100644
> --- a/drivers/acpi/osl.c
> +++ b/drivers/acpi/osl.c
> @@ -104,6 +104,7 @@ struct acpi_ioremap {
>  	void __iomem *virt;
>  	acpi_physical_address phys;
>  	acpi_size size;
> +	struct kref ref;
>  };
>  
>  static LIST_HEAD(acpi_ioremaps);
> @@ -245,15 +246,28 @@ acpi_physical_address __init acpi_os_get_root_pointer(void)
>  }
>  
>  /* Must be called with 'acpi_ioremap_lock' or RCU read lock held. */
> -static void __iomem *
> -acpi_map_vaddr_lookup(acpi_physical_address phys, acpi_size size)
> +static struct acpi_ioremap *
> +acpi_map_lookup(acpi_physical_address phys, acpi_size size)
>  {
>  	struct acpi_ioremap *map;
>  
>  	list_for_each_entry_rcu(map, &acpi_ioremaps, list)
>  		if (map->phys <= phys &&
>  		    phys + size <= map->phys + map->size)
> -			return map->virt + (phys - map->phys);
> +			return map;
> +
> +	return NULL;
> +}
> +
> +/* Must be called with 'acpi_ioremap_lock' or RCU read lock held. */
> +static void __iomem *
> +acpi_map_vaddr_lookup(acpi_physical_address phys, unsigned int size)
> +{
> +	struct acpi_ioremap *map;
> +
> +	map = acpi_map_lookup(phys, size);
> +	if (map)
> +		return map->virt + (phys - map->phys);
>  
>  	return NULL;
>  }
> @@ -265,7 +279,8 @@ acpi_map_lookup_virt(void __iomem *virt, acpi_size size)
>  	struct acpi_ioremap *map;
>  
>  	list_for_each_entry_rcu(map, &acpi_ioremaps, list)
> -		if (map->virt == virt && map->size == size)
> +		if (map->virt <= virt &&
> +		    virt + size <= map->virt + map->size)
>  			return map;
>  
>  	return NULL;
> @@ -274,9 +289,10 @@ acpi_map_lookup_virt(void __iomem *virt, acpi_size size)
>  void __iomem *__init_refok
>  acpi_os_map_memory(acpi_physical_address phys, acpi_size size)
>  {
> -	struct acpi_ioremap *map;
> -	unsigned long flags;
> +	struct acpi_ioremap *map, *tmp_map;
> +	unsigned long flags, pg_sz;
>  	void __iomem *virt;
> +	phys_addr_t pg_off;
>  
>  	if (phys > ULONG_MAX) {
>  		printk(KERN_ERR PREFIX "Cannot map memory that high\n");
> @@ -290,7 +306,9 @@ acpi_os_map_memory(acpi_physical_address phys, acpi_size size)
>  	if (!map)
>  		return NULL;
>  
> -	virt = ioremap(phys, size);
> +	pg_off = round_down(phys, PAGE_SIZE);
> +	pg_sz = round_up(phys + size, PAGE_SIZE) - pg_off;
> +	virt = ioremap(pg_off, pg_sz);
>  	if (!virt) {
>  		kfree(map);
>  		return NULL;

Why not check the existing map (that is, acpi_map_lookup()) before the
ioremap()? In APEI tables, several GAS may be in same page, so we need
ioremap() for the first page only.

Best Regards,
Huang Ying

> @@ -298,21 +316,40 @@ acpi_os_map_memory(acpi_physical_address phys, acpi_size size)
>  
>  	INIT_LIST_HEAD(&map->list);
>  	map->virt = virt;
> -	map->phys = phys;
> -	map->size = size;
> +	map->phys = pg_off;
> +	map->size = pg_sz;
> +	kref_init(&map->ref);
>  
>  	spin_lock_irqsave(&acpi_ioremap_lock, flags);
> +	/* Check if page has already been mapped. */
> +	tmp_map = acpi_map_lookup(phys, size);
> +	if (tmp_map) {
> +		kref_get(&tmp_map->ref);
> +		spin_unlock_irqrestore(&acpi_ioremap_lock, flags);
> +		iounmap(map->virt);
> +		kfree(map);
> +		return tmp_map->virt + (phys - tmp_map->phys);
> +	}
>  	list_add_tail_rcu(&map->list, &acpi_ioremaps);
>  	spin_unlock_irqrestore(&acpi_ioremap_lock, flags);
>  
> -	return virt;
> +	return map->virt + (phys - map->phys);
>  }
>  EXPORT_SYMBOL_GPL(acpi_os_map_memory);
>  
> +static void acpi_kref_del_iomap(struct kref *ref)
> +{
> +	struct acpi_ioremap *map;
> +
> +	map = container_of(ref, struct acpi_ioremap, ref);
> +	list_del_rcu(&map->list);
> +}
> +
>  void __ref acpi_os_unmap_memory(void __iomem *virt, acpi_size size)
>  {
>  	struct acpi_ioremap *map;
>  	unsigned long flags;
> +	int del;
>  
>  	if (!acpi_gbl_permanent_mmap) {
>  		__acpi_unmap_table(virt, size);
> @@ -328,9 +365,12 @@ void __ref acpi_os_unmap_memory(void __iomem *virt, acpi_size size)
>  		return;
>  	}
>  
> -	list_del_rcu(&map->list);
> +	del = kref_put(&map->ref, acpi_kref_del_iomap);
>  	spin_unlock_irqrestore(&acpi_ioremap_lock, flags);
>  
> +	if (!del)
> +		return;
> +
>  	synchronize_rcu();
>  	iounmap(map->virt);
>  	kfree(map);
>