From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gerrit Renker Date: Fri, 13 Apr 2007 09:01:41 +0000 Subject: Re: [PATCH 07/29] Use skb timestamp for receiver side Message-Id: <200704131001.41407@strip-the-willow> List-Id: References: <20070412211454.GH21292@ghostprotocols.net> In-Reply-To: <20070412211454.GH21292@ghostprotocols.net> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: dccp@vger.kernel.org Same comment. Please do read the documentation accompanying the patch. Quoting David Miller: | From: "Ian McDonald" | Date: Fri, 13 Apr 2007 09:50:30 +1200 | | > I didn't know this time stamping was expensive but I knew the way we | > were trying to optimise LAN is wrong. I say LAN because a few | > microseconds or even milliseconds difference on a WAN link makes | > bugger all difference in throughput. DCCP takes into account operating | > system granularity etc and if we are running lossless (i.e. receiver | > can cope with receiving link at full speed) then we can transmit at | > line speed. I've tested this myself. | | You want the scheduling delays and other issues that can | delay DCCP input packet processing to get factored into | the RTT, so that the sender will pace properly. | | Trying to get perfect timestamping and RTT measurements, | and ignoring scheduling delays, is quite foolhardy and shows | a lack of understanding of how queueing really works. | |