linux-kernel - Re: [PATCH] Moving spinlock to struct usb

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Message-Id: <200801260021.50786.david-b@pacbell.net>
Date:	Sat, 26 Jan 2008 00:21:50 -0800
From:	David Brownell <david-b@...bell.net>
To:	romlinux@...il.com
Cc:	greg@...ah.com, stern@...land.harvard.edu,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Moving spinlock to struct usb_hcd

On Friday 25 January 2008, Romit Dasgupta wrote:
> This should help
> reduce contention to usb during high load where i/o is happening  to
> multiple hcds.

Looking at how this lock is used, contention doesn't look likely
to be an issue.  It's never held for long ...

> @@ -1106,9 +1103,9 @@ EXPORT_SYMBOL_GPL(usb_hcd_check_unlink_urb);
>  void usb_hcd_unlink_urb_from_ep(struct usb_hcd *hcd, struct urb *urb)
>  {
>         /* clear all state linking urb to this dev (and hcd) */
> -       spin_lock(&hcd_urb_list_lock);
> +       spin_lock(&hcd->hcd_urb_list_lock);
>         list_del_init(&urb->urb_list);
> -       spin_unlock(&hcd_urb_list_lock);
> +       spin_unlock(&hcd->hcd_urb_list_lock);
>  }
>  EXPORT_SYMBOL_GPL(usb_hcd_unlink_urb_from_ep);
>  

Do you have any proof that contention is an actual problem?
Because otherwise I see no benefit to such a change.

- Dave
 
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