On Fri, Sep 24, 2010 at 11:27 AM, Patrick Cable <p...@pcable.net> wrote:
> On Fri, Sep 24, 2010 at 12:37 AM, <cpol...@surewest.net> wrote: > > What's going on over the wire? > > Something wiresharky: Statistcs -> TCP stream graph -> > > throughput graph. Might be revealing. > > I was running iftop to get a handle on what's going on over the wire. > Not as in depth as wireshark, but it gives me a graph and a more data > to start with. I ran it on the desktop receiving information from the > FPGA and the data server receiving data from the desktop. > > On the desktop: > - FPGA pushes data at a constant 4.76MB/sec, desktop receives that > just fine, no burstiness. > - The desktop seems to push data to nfs at anywhere from the > 14.6Mb/sec to 29Mb/sec > - The desktop receives NFS data at about 22.7Mb/sec constant > (sometimes it jumps to 24.7Mb/sec, but its rare) > > On the server: > - Server is sending NFS data to desktop at 22.6Mb/sec (I'm not going > to sweat over .01Mb/sec difference) > - Server is receiving NFS data with the same kind of bursts. > > It seems like the burstiness continues, but the dropped packet rate > reduces dramatically if the following are set: > /sbin/sysctl net.core.rmem_max=33554432 > /sbin/sysctl net.core.wmem_max=33554432 > /sbin/sysctl net.ipv4.tcp_rmem="4096 87380 33554432" > /sbin/sysctl net.ipv4.tcp_wmem="4096 65536 33554432" > /sbin/sysctl net.ipv4.tcp_no_metrics_save=1 > > which points to issues with the TCP stack. > > Is NFS over UDP worth trying, or am I going to run into similar > things, except not with TCP retransmit but with NFS UDP retrainsmit? > > Wireshark does a good job in pointing out what's wrong with TCP sessions. Keep an eye for window zero/full errors. What options are you using to mount the NFS share ? Depending on your safety requirements, you might want to try async/sync and different rsize/wsize values. You can also try to get some statistics (IOPS and throughput) from iozone writing to the mount point. Remember to adjust record size and thread count to your reality. -- Giovanni Tirloni gtirl...@sysdroid.com
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