netdev - Re: [PATCH] Fix tx transfer padding for full-speed USB

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Message-Id: <20120424.002808.1711965470884592541.davem@davemloft.net>
Date:	Tue, 24 Apr 2012 00:28:08 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	inguin@....de
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] Fix tx transfer padding for full-speed USB

From: Ingo van Lil <inguin@....de>
Date: Fri, 20 Apr 2012 12:00:21 +0200

> -	padlen = ((skb->len + 4) % 512) ? 0 : 4;
> +	padlen = ((skb->len + 4) % dev->maxpacket) ? 0 : 4;

This is now an expensive modulus operation, instead of
a cheap mask.

Since you know that dev->maxpacket is always a power of two, tell the
compiler this so it can still optimize the expression by changing this
to "& (dev->maxpacket - 1)" and we'll thus avoid the costly modulus.
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