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Subject[PATCH 02/10] iommu/amd: turn dev_data_list into a lock less list
Date
alloc_dev_data() adds new items to dev_data_list and search_dev_data()
is searching for items in this list. Both protect the access to the list
with a spinlock.
There is no need to navigate forth and back within the list and there is
also no deleting of a specific item. This qualifies the list to become a
lock less list and as part of this, the spinlock can be removed.
With this change the ordering of those items within the list is changed:
before the change new items were added to the end of the list, now they
are added to the front. I don't think it matters but wanted to mention
it.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
drivers/iommu/amd_iommu.c | 28 ++++++++++------------------
drivers/iommu/amd_iommu_types.h | 2 +-
2 files changed, 11 insertions(+), 19 deletions(-)

diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
index b50dcb17c68f..0e57ce2c258b 100644
--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -83,8 +83,7 @@
static DEFINE_RWLOCK(amd_iommu_devtable_lock);

/* List of all available dev_data structures */
-static LIST_HEAD(dev_data_list);
-static DEFINE_SPINLOCK(dev_data_list_lock);
+static LLIST_HEAD(dev_data_list);

LIST_HEAD(ioapic_map);
LIST_HEAD(hpet_map);
@@ -203,40 +202,33 @@ static struct dma_ops_domain* to_dma_ops_domain(struct protection_domain *domain
static struct iommu_dev_data *alloc_dev_data(u16 devid)
{
struct iommu_dev_data *dev_data;
- unsigned long flags;

dev_data = kzalloc(sizeof(*dev_data), GFP_KERNEL);
if (!dev_data)
return NULL;

dev_data->devid = devid;
-
- spin_lock_irqsave(&dev_data_list_lock, flags);
- list_add_tail(&dev_data->dev_data_list, &dev_data_list);
- spin_unlock_irqrestore(&dev_data_list_lock, flags);
-
ratelimit_default_init(&dev_data->rs);

+ llist_add(&dev_data->dev_data_list, &dev_data_list);
return dev_data;
}

static struct iommu_dev_data *search_dev_data(u16 devid)
{
struct iommu_dev_data *dev_data;
- unsigned long flags;
+ struct llist_node *node;

- spin_lock_irqsave(&dev_data_list_lock, flags);
- list_for_each_entry(dev_data, &dev_data_list, dev_data_list) {
+ if (llist_empty(&dev_data_list))
+ return NULL;
+
+ node = dev_data_list.first;
+ llist_for_each_entry(dev_data, node, dev_data_list) {
if (dev_data->devid == devid)
- goto out_unlock;
+ return dev_data;
}

- dev_data = NULL;
-
-out_unlock:
- spin_unlock_irqrestore(&dev_data_list_lock, flags);
-
- return dev_data;
+ return NULL;
}

static int __last_alias(struct pci_dev *pdev, u16 alias, void *data)
diff --git a/drivers/iommu/amd_iommu_types.h b/drivers/iommu/amd_iommu_types.h
index da886b0095aa..1c9b080276c9 100644
--- a/drivers/iommu/amd_iommu_types.h
+++ b/drivers/iommu/amd_iommu_types.h
@@ -627,7 +627,7 @@ struct devid_map {
*/
struct iommu_dev_data {
struct list_head list; /* For domain->dev_list */
- struct list_head dev_data_list; /* For global dev_data_list */
+ struct llist_node dev_data_list; /* For global dev_data_list */
struct protection_domain *domain; /* Domain the device is bound to */
u16 devid; /* PCI Device ID */
u16 alias; /* Alias Device ID */
--
2.16.2
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