Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762900AbYAUX0M (ORCPT ); Mon, 21 Jan 2008 18:26:12 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756994AbYAUXZy (ORCPT ); Mon, 21 Jan 2008 18:25:54 -0500 Received: from zcars04e.nortel.com ([47.129.242.56]:51304 "EHLO zcars04e.nortel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756842AbYAUXZx (ORCPT ); Mon, 21 Jan 2008 18:25:53 -0500 Message-ID: <479529DF.5030707@nortel.com> Date: Mon, 21 Jan 2008 17:25:19 -0600 From: "Chris Friesen" User-Agent: Mozilla Thunderbird 1.0.2-6 (X11/20050513) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Eric Dumazet CC: netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: questions on NAPI processing latency and dropped network packets References: <478654C3.60806@nortel.com> <4794F848.9020402@nortel.com> <47950F1D.4010508@cosmosbay.com> In-Reply-To: <47950F1D.4010508@cosmosbay.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-OriginalArrivalTime: 21 Jan 2008 23:25:23.0177 (UTC) FILETIME=[E5417590:01C85C84] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1714 Lines: 44 Eric Dumazet wrote: > Chris Friesen a ?crit : > >> I've done some further digging, and it appears that one of the >> problems we may be facing is very high instantaneous traffic rates. >> >> Instrumentation showed up to 222K packets/sec for short periods (at >> least 1.1 ms, possibly longer), although the long-term average is down >> around 14-16K packets/sec. > > > Instrumentation done where exactly ? I added some code to e1000_clean_rx_irq() to track rx_fifo drops, total packets received, and an accurate timestamp. If rx_fifo errors changed, it would dump the information. >> Is there anything else we can do to minimize the latency of network >> packet processing and avoid having to crank the rx ring size up so high? > You have some tasks that disable softirqs too long. Sometimes, bumping > RX ring size is OK (but you will still have delays), sometimes it is not > an option, since 4096 is the limit on current hardware. I added some instrumentation to take timestamps in __do_softirq() as well. Based on these timestamps, I can see the following code sequence: 2374604616 usec, start processing softirqs in __do_softirq() 2374610337 usec, log values in e1000_clean_rx_irq() 2374611411 usec, log values in e1000_clean_rx_irq() In between the successive calls to e1000_clean_rx_irq() the rx_fifo counts went up. Does anyone have any patchsets to track down what softirqs are taking a long time, and/or who's disabling softirqs? Chris -- 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/