[Lustre-discuss] LNET Performance Issue

Barberi, Carl E carl.e.barberi at lmco.com
Wed Feb 15 11:30:53 PST 2012

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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