netdev - Re: [PATCH net-next 2/2] tcp: include locally failed retries in retransmission stats

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Message-Id: <20170129.191743.1962744836477746399.davem@davemloft.net>
Date:   Sun, 29 Jan 2017 19:17:43 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     ycheng@...gle.com
Cc:     netdev@...r.kernel.org, ncardwell@...gle.com, edumazet@...gle.com,
        soheil@...gle.com
Subject: Re: [PATCH net-next 2/2] tcp: include locally failed retries in
 retransmission stats

From: Yuchung Cheng <ycheng@...gle.com>
Date: Fri, 27 Jan 2017 16:24:39 -0800

> Currently the retransmission stats are not incremented if the
> retransmit fails locally. But we always increment the other packet
> counters that track total packet/bytes sent.  Awkwardly while we
> don't count these failed retransmits in RETRANSSEGS, we do count
> them in FAILEDRETRANS.
> 
> If the qdisc is dropping many packets this could under-estimate
> TCP retransmission rate substantially from both SNMP or per-socket
> TCP_INFO stats. This patch changes this by always incrementing
> retransmission stats on retransmission attempts and failures.
> 
> Another motivation is to properly track retransmists in
> SCM_TIMESTAMPING_OPT_STATS. Since SCM_TSTAMP_SCHED collection is
> triggered in tcp_transmit_skb(), If tp->total_retrans is incremented
> after the function, we'll always mis-count by the amount of the
> latest retransmission.
> 
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
> Signed-off-by: Soheil Hassas Yeganeh <soheil@...gle.com>
> Acked-by: Neal Cardwell <ncardwell@...gle.com>
> Acked-by: Eric Dumazet <edumazet@...gle.com>

Also applied, thank you.