[Lustre-discuss] LNET Performance Issue

Kevin Van Maren KVanMaren at fusionio.com
Wed Feb 15 12:25:05 PST 2012

Perhaps someone else here has a thought, but it does not make sense to me that loading SDP (which accelerates TCP traffic by by-passing the TCP stack) makes lnet faster if you are using <ip>@o2ib, and _not_ <ip>@tcp0 for your NIDs.

Any chance you've configured both TCP and O2IB nids on the machine, and it is somehow picking the TCP nids to use?

Can you confirm the "lctl list_nids" output, and your lustre/lnet sections of your modprobe.conf?


On Feb 15, 2012, at 12:30 PM, Barberi, Carl E wrote:

We are having issues with LNET performance over Infiniband.  We have a configuration with a single MDT and six (6) OSTs.  The Lustre client I am using to test is configured to use 6 stripes (lfs setstripe -c  6 /mnt/lustre).  When I perform a test using the following command:

                dd if=/dev/zero of=/mnt/lustre/test.dat bs=1M count=2000

I typically get a write rate of about 815 MB/s, and we never exceed 848 MB/s.  When I run obdfilter-survey, we easily get about 3-4GB/s write speed, but when I run a series of lnet-selftests, the read and write rates range from 850MB/s – 875MB/s max.  I have performed the following optimizations to increase the data rate:

On the Client:
lctl set_param osc.*.checksums=0
lctl set_param osc.*.max_dirty_mb=256

On the OSTs
lctl set_param obdfilter.*.writethrough_cache_enable=0
lctl set_param obdfilter.*.read_cache_enable=0

echo 4096 > /sys/block/<devices>/queue/nr_requests

I have also loaded the ib_sdp module, which also brought an increase in speed.  However, we need to be able to record at no less than 1GB/s, which we cannot achieve right now.  Any thoughts on how I can optimize LNET, which clearly seems to be the bottleneck?

Thank you for any help you can provide,
Carl Barberi

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