From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gerrit Renker Date: Sun, 15 Apr 2007 16:15:32 +0000 Subject: Re: Sensitivity of TFRC throughput equation wrt to changes of RTT Message-Id: <200704151715.32852@strip-the-willow> List-Id: References: <200704131303.03072@strip-the-willow> In-Reply-To: <200704131303.03072@strip-the-willow> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: dccp@vger.kernel.org Many thanks indeed for the input - referred to in the other email as well. | So my primary suggstion is to accept that there is a limit to | how accurate you can get timestamps, there is also a specific | regime under which fine-RTT measurements matter, and therefore | the algorithm chosen has to match that reality. | I think that by building on such realities we stand a better chance of arriving at a workable solution than by blindly trying to cast a specification into code. There is some revision to be done where your input is very helpful. I hope that Eddie will incorporate/pick up the point to bypass the congestion control when RTTs are low. Ian and Eddie seem to have differing opinions regarding RTT accuracy and I think I also need to check. ( If only we could use jiffie-based algorithm, that would axe the cost of all these gettimeofdays (they still exist, even after retracting the skb_get_timestamp patches). There is this really nice TCP algorithm which doesn't use timestamps, tcp_rcv_rtt_update() in tcp_input.c . )