Patchwork [04/16] dma-debug: add allocator code

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Submitter Joerg Roedel
Date Jan. 9, 2009, 4:19 p.m.
Message ID <1231517970-20288-5-git-send-email-joerg.roedel@amd.com>
Download mbox | patch
Permalink /patch/17553/
State Not Applicable
Delegated to: David Miller
Headers show

Comments

Joerg Roedel - Jan. 9, 2009, 4:19 p.m.
Impact: add allocator code for struct dma_debug_entry

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
---
 lib/dma-debug.c |   57 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 57 insertions(+), 0 deletions(-)
Ingo Molnar - Jan. 10, 2009, 11:43 p.m.
* Joerg Roedel <joerg.roedel@amd.com> wrote:

> +		printk(KERN_ERR "DMA-API: debugging out of memory "
> +				"- disabling\n");

btw., i'd suggest to not break kernel messages mid-string, but do 
something like this instead:

> +		printk(KERN_ERR
		 "DMA-API: debugging out of memory - disabling\n");

Also, i'd use WARN() - it might be useful to see what callsite depleted 
the pool.

> +	entry = list_entry(free_entries.next, struct dma_debug_entry, list);
> +	list_del(&entry->list);
> +	memset(entry, 0, sizeof(*entry));
> +
> +	num_free_entries -= 1;
> +	if (num_free_entries < min_free_entries)
> +		min_free_entries = num_free_entries;

unlikely() i guess.

Regarding the entry pool locking:

> +static void dma_entry_free(struct dma_debug_entry *entry)
> +{
> +	unsigned long flags;
> +
> +	/*
> +	 * add to beginning of the list - this way the entries are
> +	 * more likely cache hot when they are reallocated.
> +	 */
> +	spin_lock_irqsave(&free_entries_lock, flags);
> +	list_add(&entry->list, &free_entries);
> +	num_free_entries += 1;
> +	spin_unlock_irqrestore(&free_entries_lock, flags);

it might make sense to cache entries in the buckets - hence reuse the 
bucket spinlock. This means a somewhat higher effective pool size, but it 
also avoids a global lock.

	Ingo
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Patch

diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index 74a0f36..c5444d4 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -49,6 +49,16 @@  struct hash_bucket {
 
 /* Hash list to save the allocated dma addresses */
 static struct hash_bucket dma_entry_hash[HASH_SIZE];
+/* List of pre-allocated dma_debug_entry's */
+static LIST_HEAD(free_entries);
+/* Lock for the list above */
+static DEFINE_SPINLOCK(free_entries_lock);
+
+/* Global disable flag - will be set in case of an error */
+static bool global_disable __read_mostly;
+
+static u32 num_free_entries;
+static u32 min_free_entries;
 
 /*
  * Hash related functions
@@ -138,3 +148,50 @@  static void add_dma_entry(struct dma_debug_entry *entry)
 	put_hash_bucket(bucket, &flags);
 }
 
+/* struct dma_entry allocator
+ *
+ * The next two functions implement the allocator for
+ * struct dma_debug_entries.
+ */
+static struct dma_debug_entry *dma_entry_alloc(void)
+{
+	struct dma_debug_entry *entry = NULL;
+	unsigned long flags;
+
+	spin_lock_irqsave(&free_entries_lock, flags);
+
+	if (list_empty(&free_entries)) {
+		printk(KERN_ERR "DMA-API: debugging out of memory "
+				"- disabling\n");
+		global_disable = true;
+		goto out;
+	}
+
+	entry = list_entry(free_entries.next, struct dma_debug_entry, list);
+	list_del(&entry->list);
+	memset(entry, 0, sizeof(*entry));
+
+	num_free_entries -= 1;
+	if (num_free_entries < min_free_entries)
+		min_free_entries = num_free_entries;
+
+out:
+	spin_unlock_irqrestore(&free_entries_lock, flags);
+
+	return entry;
+}
+
+static void dma_entry_free(struct dma_debug_entry *entry)
+{
+	unsigned long flags;
+
+	/*
+	 * add to beginning of the list - this way the entries are
+	 * more likely cache hot when they are reallocated.
+	 */
+	spin_lock_irqsave(&free_entries_lock, flags);
+	list_add(&entry->list, &free_entries);
+	num_free_entries += 1;
+	spin_unlock_irqrestore(&free_entries_lock, flags);
+}
+