From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from moutng.kundenserver.de (moutng.kundenserver.de [212.227.126.183]) by ozlabs.org (Postfix) with ESMTP id B33FFDDD0D for ; Sat, 25 Aug 2007 05:10:21 +1000 (EST) From: Bodo Eggert <7eggert@gmx.de> Subject: Re: RFC: issues concerning the next NAPI interface To: Linas Vepstas , Jan-Bernd Themann , netdev , Thomas Klein , Jan-Bernd Themann , linux-kernel , linux-ppc , Christoph Raisch , Marcus Eder , Stefan Roscher Date: Fri, 24 Aug 2007 21:04:56 +0200 References: <8VHRR-45R-17@gated-at.bofh.it> <8VKwj-8ke-27@gated-at.bofh.it> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Message-Id: Reply-To: 7eggert@gmx.de List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Linas Vepstas wrote: > On Fri, Aug 24, 2007 at 03:59:16PM +0200, Jan-Bernd Themann wrote: >> 3) On modern systems the incoming packets are processed very fast. Especially >> on SMP systems when we use multiple queues we process only a few packets >> per napi poll cycle. So NAPI does not work very well here and the interrupt >> rate is still high. > > I saw this too, on a system that is "modern" but not terribly fast, and > only slightly (2-way) smp. (the spidernet) > > I experimented wih various solutions, none were terribly exciting. The > thing that killed all of them was a crazy test case that someone sprung on > me: They had written a worst-case network ping-pong app: send one > packet, wait for reply, send one packet, etc. > > If I waited (indefinitely) for a second packet to show up, the test case > completely stalled (since no second packet would ever arrive). And if I > introduced a timer to wait for a second packet, then I just increased > the latency in the response to the first packet, and this was noticed, > and folks complained. Possible solution / possible brainfart: Introduce a timer, but don't start to use it to combine packets unless you receive n packets within the timeframe. If you receive less than m packets within one timeframe, stop using the timer. The system should now have a decent response time when the network is idle, and when the network is busy, nobody will complain about the latency.-) -- Funny quotes: 22. When everything's going your way, you're in the wrong lane and and going the wrong way. Friß, Spammer: rsRxhvmk@CaR.7eggert.dyndns.org m@z3T.7eggert.dyndns.org