netdev - RE: [net-next 5/8] net/mlx5e: Calc vlan_tag

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Date:   Wed, 1 Feb 2017 11:20:05 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Saeed Mahameed' <saeedm@...lanox.com>,
        "David S. Miller" <davem@...emloft.net>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [net-next 5/8] net/mlx5e: Calc vlan_tag_present only once on
 xmit

From: Saeed Mahameed
> Sent: 31 January 2017 20:59
> Cache skb_vlan_tag_present(skb) and pass it wherever needed in xmit
> routines.
...

Does this actually generate better code?
It is quite likely that your 'vlan_present' variable ends up being on stack.
Whereas the 'skb' is likely to be in a register.
In which case the two loads are likely to be must the same and your
change has added a write to the stack.

	David