linux-kernel - Re: [PATCH 2/3] staging: greybus: loopback.c: do insertion in O(n) instead of O(n lg n)

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Date:   Tue, 23 Oct 2018 18:20:09 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Bryan O'Donoghue <pure.logic@...us-software.ie>,
        Johan Hovold <johan@...nel.org>, Alex Elder <elder@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     greybus-dev@...ts.linaro.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] staging: greybus: loopback.c: do insertion in O(n)
 instead of O(n lg n)

On 2018-10-11 01:03, Bryan O'Donoghue wrote:
> On 05/10/2018 15:28, Rasmus Villemoes wrote:
>> Signed-off-by: Rasmus Villemoes<linux@...musvillemoes.dk>
>> ---
>> I have no idea if the performance matters (it probably doesn't). Feel
>> free to ignore this and the followup cleanup.
> 
> What's the problem you're fixing here ?
> 
> Is it tested ?

I got curious why one would want to keep a linked list sorted in the
first place (it can't be for doing binary searches). But it seems that
gb_loopback_device::list is unused, along with the list_op_async. Given
that the below compiles, doesn't that prove that the code is
dead/unused, or what am I missing?

diff --git a/drivers/staging/greybus/loopback.c
b/drivers/staging/greybus/loopback.c
index 7080294f705c..e4d42c1dc284 100644
--- a/drivers/staging/greybus/loopback.c
+++ b/drivers/staging/greybus/loopback.c
@@ -47,8 +47,6 @@ struct gb_loopback_device {

 	/* We need to take a lock in atomic context */
 	spinlock_t lock;
-	struct list_head list;
-	struct list_head list_op_async;
 	wait_queue_head_t wq;
 };

@@ -68,7 +66,6 @@ struct gb_loopback {
 	struct kfifo kfifo_lat;
 	struct mutex mutex;
 	struct task_struct *task;
-	struct list_head entry;
 	struct device *dev;
 	wait_queue_head_t wq;
 	wait_queue_head_t wq_completion;
@@ -987,37 +984,6 @@ static const struct file_operations
gb_loopback_debugfs_latency_ops = {
 	.release	= single_release,
 };

-static int gb_loopback_bus_id_compare(void *priv, struct list_head *lha,
-				      struct list_head *lhb)
-{
-	struct gb_loopback *a = list_entry(lha, struct gb_loopback, entry);
-	struct gb_loopback *b = list_entry(lhb, struct gb_loopback, entry);
-	struct gb_connection *ca = a->connection;
-	struct gb_connection *cb = b->connection;
-
-	if (ca->bundle->intf->interface_id < cb->bundle->intf->interface_id)
-		return -1;
-	if (cb->bundle->intf->interface_id < ca->bundle->intf->interface_id)
-		return 1;
-	if (ca->bundle->id < cb->bundle->id)
-		return -1;
-	if (cb->bundle->id < ca->bundle->id)
-		return 1;
-	if (ca->intf_cport_id < cb->intf_cport_id)
-		return -1;
-	else if (cb->intf_cport_id < ca->intf_cport_id)
-		return 1;
-
-	return 0;
-}
-
-static void gb_loopback_insert_id(struct gb_loopback *gb)
-{
-	/* perform an insertion sort */
-	list_add_tail(&gb->entry, &gb_dev.list);
-	list_sort(NULL, &gb_dev.list, gb_loopback_bus_id_compare);
-}
-
 #define DEBUGFS_NAMELEN 32

 static int gb_loopback_probe(struct gb_bundle *bundle,
@@ -1113,7 +1079,6 @@ static int gb_loopback_probe(struct gb_bundle *bundle,
 	}

 	spin_lock_irqsave(&gb_dev.lock, flags);
-	gb_loopback_insert_id(gb);
 	gb_dev.count++;
 	spin_unlock_irqrestore(&gb_dev.lock, flags);

@@ -1169,7 +1134,6 @@ static void gb_loopback_disconnect(struct
gb_bundle *bundle)

 	spin_lock_irqsave(&gb_dev.lock, flags);
 	gb_dev.count--;
-	list_del(&gb->entry);
 	spin_unlock_irqrestore(&gb_dev.lock, flags);

 	device_unregister(gb->dev);
@@ -1196,8 +1160,6 @@ static int loopback_init(void)
 {
 	int retval;

-	INIT_LIST_HEAD(&gb_dev.list);
-	INIT_LIST_HEAD(&gb_dev.list_op_async);
 	spin_lock_init(&gb_dev.lock);
 	gb_dev.root = debugfs_create_dir("gb_loopback", NULL);