Date: Fri, 3 Oct 2008 10:25:23 +0100 (BST) From: Robert Watson <rwatson@FreeBSD.org> To: Danny Braniss <danny@cs.huji.ac.il> Cc: freebsd-hackers@freebsd.org, Jeremy Chadwick <koitsu@freebsd.org>, freebsd-stable@freebsd.org, Claus Guttesen <kometen@gmail.com> Subject: Re: bad NFS/UDP performance Message-ID: <alpine.BSF.1.10.0810031022140.41647@fledge.watson.org> In-Reply-To: <E1KlgnA-000F6w-NT@cs1.cs.huji.ac.il> References: <E1Kj7NA-000FXz-3F@cs1.cs.huji.ac.il> <20080926081806.GA19055@icarus.home.lan> <E1Kj9bR-000H7t-0g@cs1.cs.huji.ac.il> <20080926095230.GA20789@icarus.home.lan> <E1KjEZw-000KkH-GP@cs1.cs.huji.ac.il> <alpine.BSF.1.10.0809271114450.20117@fledge.watson.org> <E1KjY2h-0008GC-PP@cs1.cs.huji.ac.il> <b41c75520809290140i435a5f6dge5219cd03cad55fe@mail.gmail.com> <E1Klfac-000DzZ-Ie@cs1.cs.huji.ac.il> <alpine.BSF.1.10.0810030910351.41647@fledge.watson.org> <E1KlgYe-000Es2-8u@cs1.cs.huji.ac.il> <alpine.BSF.1.10.0810031003440.41647@fledge.watson.org> <E1KlgnA-000F6w-NT@cs1.cs.huji.ac.il>
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On Fri, 3 Oct 2008, Danny Braniss wrote: > gladly, but have no idea how to do LOCK_PROFILING, so some pointers would be > helpfull. The LOCK_PROFILING(9) man page isn't a bad starting point -- I find that the defaults work fine most of the time, so just use them. Turn the enable syscl on just before you begin a run, and turn it off immediately afterwards. Make sure to reset between reruns (rebooting to a new kernel is fine too!). > as a side note, many years ago I checked out NFS/TCP and it was really bad, > I even remember NetApp telling us to drop TCP, but now, things look rather > better. Wonder what caused it. Well, the virtues of TCP become more apparent with higher network speeds, as the logic to fill pipes using TCP, manage flow control, etc, is a lot more sophisticated than what's in the RPC code for using UDP. The downsides to UDP are also becoming more apparent: as network speeds go up, fragmented UDP risks IP ID collisions which could lead to data corruption, or at the very least, dropped packets. We have changed the default for NFSv3 mounts to TCP in 8.x, and talked about doing it for 7.1; unfortunately the timing wasn't quite right, so it most likely will appear in 7.2. Robert N M Watson Computer Laboratory University of Cambridge
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