Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765343AbXHXTF3 (ORCPT ); Fri, 24 Aug 2007 15:05:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758964AbXHXTFQ (ORCPT ); Fri, 24 Aug 2007 15:05:16 -0400 Received: from moutng.kundenserver.de ([212.227.126.187]:50877 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758335AbXHXTFO (ORCPT ); Fri, 24 Aug 2007 15:05:14 -0400 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 Reply-To: 7eggert@gmx.de Date: Fri, 24 Aug 2007 21:04:56 +0200 References: <8VHRR-45R-17@gated-at.bofh.it> <8VKwj-8ke-27@gated-at.bofh.it> User-Agent: KNode/0.7.2 MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8Bit Message-Id: X-be10.7eggert.dyndns.org-MailScanner-Information: See www.mailscanner.info for information X-be10.7eggert.dyndns.org-MailScanner: Found to be clean X-be10.7eggert.dyndns.org-MailScanner-From: 7eggert@gmx.de X-Provags-ID: V01U2FsdGVkX1+2cGwZ8ftRb/GDtvIhEamL8FSRlmWcMnhLBkZ xx4GmSIcf1xuFKzKCvCXkd/ke/YHP6wxq6UT4VJ2mojSOZ43Rp 266al3AVib3nY3/cUxLQw== Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1902 Lines: 34 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. Fri?, Spammer: rsRxhvmk@CaR.7eggert.dyndns.org m@z3T.7eggert.dyndns.org - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/