From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161032AbWIEUVi (ORCPT ); Tue, 5 Sep 2006 16:21:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030254AbWIEUVi (ORCPT ); Tue, 5 Sep 2006 16:21:38 -0400 Received: from wx-out-0506.google.com ([66.249.82.227]:55323 "EHLO wx-out-0506.google.com") by vger.kernel.org with ESMTP id S1030253AbWIEUVg (ORCPT ); Tue, 5 Sep 2006 16:21:36 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:to:subject:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=djZrIS6p/EDMVmi3IsFZQNQGkyg82VKCOqawA1xzZI9fLowdNVLJZTrbOe2gldHt/j0djOxVu/j9LPWnwIF9sMXwFaDtkaRT4C+M6KvzjpOuuDnhS5cAaxv0RJwiFDOtOH5rWrruAJCUuIP+NrTu0EiyBVXBULJF/Ln4lK0jvH0= Message-ID: <86b122f40609051321p4be05683x9261b5142ed2ea4f@mail.gmail.com> Date: Tue, 5 Sep 2006 22:21:35 +0200 From: "Tiemen Schut" To: linux-kernel@vger.kernel.org Subject: Re: Kernel drops ethernet packets during disk writes In-Reply-To: <44FDCEB2.6070500@degler.net> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <86b122f40609050815v664ff217kcfc82a5c9f2772ad@mail.gmail.com> <86b122f40609050906u7aafe808h5002c9f15369a744@mail.gmail.com> <44FDCEB2.6070500@degler.net> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Now this is something constructive! I can indeed maintain 350Mbit/s to disk (about 55MB/s to disk actually), and I can receive all the packets, as long as I don't try to do both things simultaniously. I'll try to increase the buffers tomorrow, will let you know how it worked out. I doubt though that the tcp buffers have any impact, we're talking raw ethernet frames here. Thanks, Tiemen On 9/5/06, Stephen Degler wrote: > Tiemen Schut wrote: > > Summary: The linux kernel appears to drop raw ethernet packets if > > another process is writing to disk. > > > > Test environment: Used a p4 1.7 GHz with gigabit interface > > point-to-point connection to another p4 (windows pc). This windows PC > > generates raw ethernet frames holding a counter and sends 'm on to the > > linux PC, at a transfer rate of 350 Mbit/s. When not writing to disk, > > everything goes quite fine. I can check the counters at the linux > > side, and will notice a minimal packet loss (< 0.001 % or so). > > > > However, for my application I want to write each and every frame to > > disk. So, I created a second app, and through a fifo the receiver app > > and the disk writer app communicate. Now I'm losing like 80% of my > > packets :o Reducing the throughput on the network doesn't really help > > (though it does help a little). > > > > Note: I tried everything in the same app first, but my guess was that > > the write operation delayed the app, so I decided to put everything in > > two apps to give the scheduler some work ;) Didn't work though. > > > > My guess would be that the kernel drops the packets because the write > > operation takes to long (how long can it take, it's just a stupid 1512 > > bytes frame). Anyway, I tried to enlarge > > .sys.net.core.netdev_max_backlog, but that didn't do the trick. > > > > This problem occures on both 2.6.13 and 2.4.idontremember. > > > > It kinda sucks, what's the use of receiving traffic if you can't write > > it to disk? > > > > I'm sending the packets using the winpcap library, and I'm receiving > > the packets using the pcap library. > > > > Any help would be _greatly_ appreciated, and if neccessary, please ask > > for additional information/used software/test results/etc. > > > > Tiemen Schut > Hi your packets are being dropped perhaps because there is no room to > store them while the disk is busy, not that you don't receive them. > > Can you sustain 35M/second to disk? If you can't do that with dd > if=/dev/zero of="foo" bs=1024k, then you can not expect to do it with > the network plus your writer. Writing > sequentially to a large modern disk you should be able to do this (large > capacity SATA or SCSI disks, or hardware raid controllers). > > You can improve matters greatly by increasing the kernel network buffers > available. This will give you more buffer room while the disk subsystem > is busy. Look at the following tuneables: you should be able to greatly > reduce packet loss by increasing them from the default values. > > net.core.rmem_max = 2500000 > net.core.wmem_max = 2500000 > net.ipv4.tcp_rmem = 4096 5000000 5000000 > net.ipv4.tcp_wmem = 4096 65536 5000000 > > I can assure you that with the proper system configuration, high network > to disk throughput is indeed possible. > > Hope this helps, > skd > >