linux-kernel - [PATCH] USB: remove 8 bytes of padding from usb_host

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Message-ID: <1341937165.1762.10.camel@castor.rsk>
Date:	Tue, 10 Jul 2012 17:19:25 +0100
From:	Richard Kennedy <richard@....demon.co.uk>
To:	Greg Kroah-Hartman <greg@...ah.com>
Cc:	linux-usb <linux-usb@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: [PATCH] USB: remove 8 bytes of padding from usb_host_interface on
 64 bit builds

Reorder elements in the usb_host_interface structure to remove 8 bytes
of padding on 64 bit builds , and so shrink it's size to 40 bytes.
    
usb_interface_descriptor is a odd size which leaves a gap that is not
big enough to hold a pointer, so moving extralen into that gap removes
the need for more padding.


Signed-off-by: Richard Kennedy <richard@....demon.co.uk>

---
patch against v3.5-rc6
compiled and tested on x86_64
I've been running this patch for several weeks with no obvious problems.
This will allow the usb_host_interface array to be a bit smaller and should
better align with the cachelines.

regards
Richard 




diff --git a/include/linux/usb.h b/include/linux/usb.h
index dea39dc..2abec02 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -77,14 +77,14 @@ struct usb_host_endpoint {
 struct usb_host_interface {
 	struct usb_interface_descriptor	desc;
 
+	int extralen;
+	unsigned char *extra;   /* Extra descriptors */
 	/* array of desc.bNumEndpoint endpoints associated with this
 	 * interface setting.  these will be in no particular order.
 	 */
 	struct usb_host_endpoint *endpoint;
 
 	char *string;		/* iInterface string, if present */
-	unsigned char *extra;   /* Extra descriptors */
-	int extralen;
 };
 
 enum usb_interface_condition {



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