Re: The anchor patch critique

Am Mittwoch, 6. Juni 2007 schrieb Pete Zaitcev:
> So, you add 24 bytes to all URBs, which are... not very thin, to be sure.
> Last time I counted they were 152 bytes apiece. Still, a 15% increase.
> I know you're a good algorithmist, are you sure you don't have any ideas?
> 
> The naive approach is to have anchor elements out of line... In a slab,
> since they are fixed-sized. What do you think?

Here's a patch to reduce padding:

--- a/include/linux/usb.h	2007-06-06 13:44:41.000000000 +0200
+++ b/include/linux/usb.h	2007-06-06 14:29:43.000000000 +0200
@@ -1142,24 +1142,24 @@ struct urb
 {
 	/* private: usb core and host controller only fields in the urb */
 	struct kref kref;		/* reference count of the URB */
+	atomic_t use_count;		/* concurrent submissions counter */
 	spinlock_t lock;		/* lock for the URB */
 	void *hcpriv;			/* private data for host controller */
-	atomic_t use_count;		/* concurrent submissions counter */
+	struct list_head anchor_list;	/* the URB may be anchored by the driver */
+	struct usb_anchor *anchor;	/* anchor to which we are chained */
 	u8 reject;			/* submissions will fail */
 
 	/* public: documented fields in the urb that can be used by drivers */
+	short status;			/* (return) non-ISO status */
+	unsigned short transfer_flags;	/* (in) URB_SHORT_NOT_OK | ...*/
+	unsigned int pipe;		/* (in) pipe information */
+	int transfer_buffer_length;	/* (in) data buffer length */
+	int actual_length;		/* (return) actual transfer length */
 	struct list_head urb_list;	/* list head for use by the urb's
 					 * current owner */
-	struct list_head anchor_list;	/* the URB may be anchored by the driver */
-	struct usb_anchor *anchor;
 	struct usb_device *dev; 	/* (in) pointer to associated device */
-	unsigned int pipe;		/* (in) pipe information */
-	int status;			/* (return) non-ISO status */
-	unsigned int transfer_flags;	/* (in) URB_SHORT_NOT_OK | ...*/
 	void *transfer_buffer;		/* (in) associated data buffer */
 	dma_addr_t transfer_dma;	/* (in) dma addr for transfer_buffer */
-	int transfer_buffer_length;	/* (in) data buffer length */
-	int actual_length;		/* (return) actual transfer length */
 	unsigned char *setup_packet;	/* (in) setup packet (control only) */
 	dma_addr_t setup_dma;		/* (in) dma addr for setup_packet */
 	int start_frame;		/* (modify) start frame (ISO) */

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