Dave Howorth wrote:

I just got some surprising performance numbers.

Some more facts and better numbers ... B packages: kernel 2.6.8-24.14 SMP x86-64, nfs-utils 1.0.6-113 C packages: kernel 2.6.11.4-21.7 SMP i586, nfs-utils 1.0.7-3

I have three systems, call them A, B and C.

I have another machine that is essentially a duplicate of B. It behaves the same, so I think I can rule out hardware faults.

A is a file server, B is supposed to be a fast server and C is my desktop. I'm trying to improve the performance of a job that normally runs on B and manipulates files on A, so I wrote a little test program. I ran it on all three machines. My test creates 10000 symlinks to a file. Symlinks and the file are accessed via NFS from A.

It was fastest on A (less than 1 second) - no surprise using local disk. It took 5 seconds on C. It took 23 seconds on B! Big surprise.

I re-mounted A's disks on B , via the main-network interface instead of the direct connect, and ran the test again: 7 seconds !!! Much better, but why?

Anybody have any thoughts on what makes B so slow?

So now it seems to be specific to an interface (they are identical interfaces). nfsstat didn't show any errors or retransmits etc.

All are connected to each other through a gigabit switch. In addition, A and B have additional gigabit NICS connected directly to each other.

Here are some system details:

A: Tyan S5350 Tiger i7320 dual 2.8 GHz Xeon, 1 GB memory, lots of SATA disks with 3ware controllers. SUSE 9.2 Intel PRO/1000 MT Dual Port NIC - quiescent during tests Intel PRO/1000 MT Dual Port NIC - direct connect to B Broadcom NetXtreme BCM5721 Gigabit NIC PCI Express - unused Broadcom NetXtreme BCM5721 Gigabit NIC PCI Express - main network

B: Tyan S2882 Thunder K8S pro, dual Opteron 242, 8 GB memory, fast SCSI local disks, SUSE 9.2 Intel EtherExpress PRO/100 S Server Adapter - unused. Broadcom NetXtreme BCM5704 Gigabit NIC - direct connect to A. Broadcom NetXtreme BCM5704 Gigabit NIC - main network.

C: Intel D925 / P4-3600, 2 GB memory, SATA local disk, SUSE 9.3, Intel 82547EI Gigabit NIC - main network

While the test is running, 'vmstat 1' on B shows lines like:

procs -----------memory------------ -swap --io- --system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa

1 0 30716 2616544 42620 4389496 0 0 0 0 5698 4616 0 5 95 0

while on C it shows:

1 0 23820 737800 322640 372736 0 0 0 0 9311 12258 1 7 93 0

So C is managing nearly twice as many interrupts and three times as many context switches per second as B.

On quiet systems, nttcp shows very similar transmit (910 Mbps) rates from both B and C to A. The receive rate to C (930 Mbps) is a bit better than to B (840 Mbps). But I don't think there's anything wrong with the basic network.

Checking the above reveals that I measured B<->A using the main-network interface. Repeating the test with the direct connect interface gives a bit lower figures (810 Mbps transmit, 720 Mbps receive). Oh, the direct connect is eth0 and the main network is eth1.

Any ideas on how to improve B's performance would be very welcome.

So I now have a workaround for my application's performance, but it would be nice to understand why the direct connection is so much slower. Thanks, Dave