netdev - Re: [PATCH net-next 3/8] tcp: use one bit in TCP_SKB

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Date:	Wed, 30 Mar 2016 23:36:00 -0400
From:	Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:	Soheil Hassas Yeganeh <soheil.kdev@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	Network Development <netdev@...r.kernel.org>,
	Willem de Bruijn <willemb@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Martin KaFai Lau <kafai@...com>,
	Soheil Hassas Yeganeh <soheil@...gle.com>
Subject: Re: [PATCH net-next 3/8] tcp: use one bit in TCP_SKB_CB to mark ACK timestamps

On Wed, Mar 30, 2016 at 6:37 PM, Soheil Hassas Yeganeh
<soheil.kdev@...il.com> wrote:
> From: Soheil Hassas Yeganeh <soheil@...gle.com>
>
> Currently, to avoid a cache line miss for accessing skb_shinfo,
> tcp_ack_tstamp skips socket that do not have
> SOF_TIMESTAMPING_TX_ACK bit set in sk_tsflags. This is
> implemented based on an implicit assumption that the
> SOF_TIMESTAMPING_TX_ACK is set via socket options for the
> duration that ACK timestamps are needed.
>
> To implement per-write timestamps, this check should be
> removed and replaced with a per-packet alternative that
> quickly skips packets missing ACK timestamps marks without
> a cache-line miss.
>
> To enable per-packet marking without a cache line miss, use
> one bit in TCP_SKB_CB to mark a whether a SKB might need a
> ack tx timestamp or not. Further checks in tcp_ack_tstamp are not
> modified and work as before.
>
> Signed-off-by: Soheil Hassas Yeganeh <soheil@...gle.com>

Acked-by: Willem de Bruijn <willemb@...gle.com>