[PATCH 1/1] acpi_init: move to full RCU free for IO mappings

[John Johansen]

On 09/23/2011 08:50 AM, Andy Whitcroft wrote:
> During acpi_init we map and unmap a large number of mappings.  The existing
> code uses 'simple' RCU based free, triggering a full sychronize_rcu()
> against the caller.  If the machine is busy (for example unpacking the
> initramfs) at the time this triggers a significant delay until all cpus
> rendevous.  Move those to a delayed RCU free callback.
> 
> For our reference platform this cuts the average acpi_init time in half,
> dropping boot time by .25s.
> 
> Signed-off-by: Andy Whitcroft <apw at canonical.com>
looks good

Acked-by: John Johansen <john.johansen at canonical.com>

> ---
>  drivers/acpi/atomicio.c |   12 +++++++++---
>  drivers/acpi/osl.c      |   16 +++++++++++-----
>  2 files changed, 20 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/acpi/atomicio.c b/drivers/acpi/atomicio.c
> index 7489b89..0a7a554 100644
> --- a/drivers/acpi/atomicio.c
> +++ b/drivers/acpi/atomicio.c
> @@ -49,6 +49,7 @@ struct acpi_iomap {
>  	unsigned long size;
>  	phys_addr_t paddr;
>  	struct kref ref;
> +	struct rcu_head iomap_rcu;
>  };
>  
>  /* acpi_iomaps_lock or RCU read lock must be held before calling */
> @@ -161,6 +162,13 @@ static void __acpi_kref_del_iomap(struct kref *ref)
>   * Used to post-unmap the specified IO memory area. The iounmap is
>   * done only if the reference count goes zero.
>   */
> +static void acpi_post_unmap_rcu(struct rcu_head *rcu)
> +{
> +	struct acpi_iomap *map = container_of(rcu, 
> +					struct acpi_iomap, iomap_rcu);
> +	iounmap(map->vaddr);
> +	kfree(map);
> +}
>  static void acpi_post_unmap(phys_addr_t paddr, unsigned long size)
>  {
>  	struct acpi_iomap *map;
> @@ -176,9 +184,7 @@ static void acpi_post_unmap(phys_addr_t paddr, unsigned long size)
>  	if (!del)
>  		return;
>  
> -	synchronize_rcu();
> -	iounmap(map->vaddr);
> -	kfree(map);
> +	call_rcu(&map->iomap_rcu, acpi_post_unmap_rcu);
>  }
>  
>  /* In NMI handler, should set silent = 1 */
> diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
> index 372f9b7..9b3a520 100644
> --- a/drivers/acpi/osl.c
> +++ b/drivers/acpi/osl.c
> @@ -105,6 +105,7 @@ struct acpi_ioremap {
>  	acpi_physical_address phys;
>  	acpi_size size;
>  	unsigned long refcount;
> +	struct rcu_head map_rcu;
>  };
>  
>  static LIST_HEAD(acpi_ioremaps);
> @@ -373,13 +374,18 @@ static void acpi_os_drop_map_ref(struct acpi_ioremap *map)
>  		list_del_rcu(&map->list);
>  }
>  
> +static void acpi_os_map_cleanup_rcu(struct rcu_head *rcu)
> +{
> +	struct acpi_ioremap *map = container_of(rcu,
> +					struct acpi_ioremap, map_rcu);
> +	iounmap(map->virt);
> +	kfree(map);
> +}
> +
>  static void acpi_os_map_cleanup(struct acpi_ioremap *map)
>  {
> -	if (!map->refcount) {
> -		synchronize_rcu();
> -		iounmap(map->virt);
> -		kfree(map);
> -	}
> +	if (!map->refcount)
> +		call_rcu(&map->map_rcu, acpi_os_map_cleanup_rcu);
>  }
>  
>  void __ref acpi_os_unmap_memory(void __iomem *virt, acpi_size size)