netdev - Re: [PATCH net-next] mlx4: optimize xmit path

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Message-Id: <1411861467.374982.172498061.37EB43B1@webmail.messagingengine.com>
Date:	Sun, 28 Sep 2014 01:44:27 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	Or Gerlitz <gerlitz.or@...il.com>
Cc:	Alexei Starovoitov <ast@...mgrid.com>,
	"David S. Miller" <davem@...emloft.net>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	John Fastabend <john.r.fastabend@...el.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Amir Vadai <amirv@...lanox.com>,
	Or Gerlitz <or.gerlitz@...il.com>
Subject: Re: [PATCH net-next] mlx4: optimize xmit path

Hi Eric,

On Sun, Sep 28, 2014, at 00:56, Eric Dumazet wrote:
> -       ring->cons += txbbs_skipped;
> +
> +       /* we want to dirty this cache line once */
> +       ACCESS_ONCE(ring->last_nr_txbb) = last_nr_txbb;
> +       ACCESS_ONCE(ring->cons) = ring_cons + txbbs_skipped;
> +

Impressive work!

I wonder if another macro might be useful for those kind of
dereferences, because ACCESS_ONCE is associated with correctness in my
mind and those usages only try to optimize access patterns.
Does OPTIMIZER_HIDE_VAR generate the same code?

Bye,
Hannes
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