[PATCH v3 2/2] USB hub_probe: put initialization before usage

[PATCH v3 2/2] USB hub_probe: put initialization before usage

[Eugene Korenevsky]

Minor optimization: move initialization immediately before usage.
This gives a chance for more accurate register allocation by the compiler.

Signed-off-by: Eugene Korenevsky <ekorenevsky@gmail.com>
---
 drivers/usb/core/hub.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 7a20980..c7f6b5f 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -1742,7 +1742,6 @@ static int hub_probe(struct usb_interface *intf, const struct usb_device_id *id)
 	struct usb_device *hdev;
 	struct usb_hub *hub;
 
-	desc = intf->cur_altsetting;
 	hdev = interface_to_usbdev(intf);
 
 	/*
@@ -1813,6 +1812,7 @@ static int hub_probe(struct usb_interface *intf, const struct usb_device_id *id)
 	}
 #endif
 
+	desc = intf->cur_altsetting;
 	if (!hub_check_descriptor_sanity(desc)) {
 		dev_err(&intf->dev, "bad descriptor, ignoring hub\n");
 		return -EIO;
-- 
2.10.2

Re: [PATCH v3 2/2] USB hub_probe: put initialization before usage

[Greg Kroah-Hartman]

On Mon, Nov 07, 2016 at 09:55:09PM +0300, Eugene Korenevsky wrote:
> Minor optimization: move initialization immediately before usage.
> This gives a chance for more accurate register allocation by the compiler.

This is a probe function, a very slow path.  Don't do micro
optimizations where they are not needed, or can not be actually
measured.

Also please just cc: the needed mailing list and maintainer for the
patch, don't go overboard for such tiny stuff.

thanks,

greg k-h