From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gerrit Renker Date: Tue, 06 Mar 2007 09:52:01 +0000 Subject: Re: CCID 3 bounded by OS scheduling granularity Message-Id: <200703060952.01629@strip-the-willow> List-Id: References: <200701221424.36105@strip-the-willow> In-Reply-To: <200701221424.36105@strip-the-willow> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: dccp@vger.kernel.org | > I have performed experiments which confirm that | > | > 1) when t_ipi < t_gran, the transmit rate is effectively out of control | > 2) when t_ipi > t_gran, the actual transmit rate is about a factor of 3 | > higher than s/t_ipi would permit. | > | > http://www.erg.abdn.ac.uk/users/gerrit/dccp/docs/packet_scheduling/ | | I've been going over this and wonder if you ever got to the bottom of | it by instrumenting it or similar as it doesn't make sense to me.... | We add t_ipi to t_nom after each packet so even coarse grained | scheduling shouldn't do this. The graphs on that web page are actually the result of instrumenting the kernel. There are further instrumentation tests, the results of which are on http://www.erg.abdn.ac.uk/users/gerrit/dccp/docs/impact_of_tx_queue_lenghts/ The problem is not in adding t_ipi, but rather in schedule_timeout which works at HZ granularity.