From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bogdan Costescu Subject: Re: [NFS] nfs performance: read only/gigE/nolock/1Tb per day Date: Tue, 23 Apr 2002 20:16:06 +0200 (CEST) Sender: owner-netdev@oss.sgi.com Message-ID: References: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: nfs@lists.sourceforge.net, Return-path: To: Trond Myklebust In-Reply-To: List-Id: netdev.vger.kernel.org [ cc-ed to netdev; the discussion was about receiving bursts of ICMP Time Exceeded messages after some large NFS datagrams could not be reassembled; sometimes down/up the interface on the receiver/reassembly side cures it ] On 23 Apr 2002, Trond Myklebust wrote: > > How big are the datagrams compared with the MTU ? With 32K > > datagrams over Ethernet, you're talking about roughly a full Rx > > ring worth of packets (32 is common for the Rx ring size)... > > It has been a while ago (I've since mothballed the machine) but I saw > it on a Pentium 90 with only 8k write sizes. 4k was fine, 8k gave > avalanches. IMHO you can't comletely eliminate hardware related problems: apart from having a slow CPU, some early PCI implementations were buggy (although you don't say if it's PCI or ISA and what's the link speed). > > Does the other side sees these messages ? > > IIRC, yes, and the server was resending the datagrams. From the code, > it looks as if there is no attempt to stop loopback situations > occurring when this goes on: > i.e. resending an ICMP when the server resends a datagram which times > out again appears to be possible. This might be what was happening... That's why I cc-ed netdev. My knowledge above the driver level is close to non-existant... -- Bogdan Costescu IWR - Interdisziplinaeres Zentrum fuer Wissenschaftliches Rechnen Universitaet Heidelberg, INF 368, D-69120 Heidelberg, GERMANY Telephone: +49 6221 54 8869, Telefax: +49 6221 54 8868 E-mail: Bogdan.Costescu@IWR.Uni-Heidelberg.De