From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH v2 net-next] tcp-tso: do not split TSO packets at retransmit time Date: Sun, 24 Apr 2016 14:44:20 -0400 (EDT) Message-ID: <20160424.144420.594314082130628842.davem@davemloft.net> References: <1461261323-14355-1-git-send-email-edumazet@google.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, ncardwell@google.com, ycheng@google.com, eric.dumazet@gmail.com To: edumazet@google.com Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:52623 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752009AbcDXSoZ (ORCPT ); Sun, 24 Apr 2016 14:44:25 -0400 In-Reply-To: <1461261323-14355-1-git-send-email-edumazet@google.com> Sender: netdev-owner@vger.kernel.org List-ID: From: Eric Dumazet Date: Thu, 21 Apr 2016 10:55:23 -0700 > Linux TCP stack painfully segments all TSO/GSO packets before retransmits. > > This was fine back in the days when TSO/GSO were emerging, with their > bugs, but we believe the dark age is over. > > Keeping big packets in write queues, but also in stack traversal > has a lot of benefits. > - Less memory overhead, because write queues have less skbs > - Less cpu overhead at ACK processing. > - Better SACK processing, as lot of studies mentioned how > awful linux was at this ;) > - Less cpu overhead to send the rtx packets > (IP stack traversal, netfilter traversal, drivers...) > - Better latencies in presence of losses. > - Smaller spikes in fq like packet schedulers, as retransmits > are not constrained by TCP Small Queues. > > 1 % packet losses are common today, and at 100Gbit speeds, this > translates to ~80,000 losses per second. > Losses are often correlated, and we see many retransmit events > leading to 1-MSS train of packets, at the time hosts are already > under stress. > > Signed-off-by: Eric Dumazet > Acked-by: Yuchung Cheng Applied, thanks Eric.