From mboxrd@z Thu Jan  1 00:00:00 1970
From: Martin KaFai Lau <kafai@fb.com>
Subject: Re: [PATCH net-next 2/2] tcp: remove a redundant check for
 SKBTX_ACK_TSTAMP
Date: Wed, 27 Apr 2016 11:19:38 -0700
Message-ID: <20160427181938.GA54673@kafai-mba.local>
References: <1461617473-11349-1-git-send-email-soheil.kdev@gmail.com>
 <1461617473-11349-2-git-send-email-soheil.kdev@gmail.com>
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Cc: <davem@davemloft.net>, <netdev@vger.kernel.org>,
	<willemb@google.com>, <edumazet@google.com>, <ycheng@google.com>,
	<ncardwell@google.com>, Soheil Hassas Yeganeh <soheil@google.com>
To: Soheil Hassas Yeganeh <soheil.kdev@gmail.com>
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On Mon, Apr 25, 2016 at 04:51:13PM -0400, Soheil Hassas Yeganeh wrote:
> From: Soheil Hassas Yeganeh <soheil@google.com>
>
> txstamp_ack in tcp_skb_cb is set iff the SKBTX_ACK_TSTAMP
> flag is set for an skb. Thus, it is not required to check
> shinfo->tx_flags if the txstamp_ack bit is checked.
>
> Remove the check on shinfo->tx_flags & SKBTX_ACK_TSTAMP, since
> it has already been checked using the txstamp_ack bit.
>
> Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
> ---
>  net/ipv4/tcp_input.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 967520d..2f3fd92 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -3087,8 +3087,7 @@ static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
>  		return;
>
>  	shinfo = skb_shinfo(skb);
> -	if ((shinfo->tx_flags & SKBTX_ACK_TSTAMP) &&
> -	    !before(shinfo->tskey, prior_snd_una) &&
> +	if (!before(shinfo->tskey, prior_snd_una) &&
>  	    before(shinfo->tskey, tcp_sk(sk)->snd_una))
>  		__skb_tstamp_tx(skb, NULL, sk, SCM_TSTAMP_ACK);
>  }
> --
> 2.8.0.rc3.226.g39d4020
>
Acked-by: Martin KaFai Lau <kafai@fb.com>

Can it be one step further and completely remove SKBTX_ACK_TSTAMP?
like what Willem has also suggested here:
http://www.spinics.net/lists/netdev/msg374231.html

It seems no one else is using the SKBTX_ACK_TSTAMP except TCP.