This bug was fixed in the package lmbench - 3.0-a9-1.3ubuntu0.1
---------------
lmbench (3.0-a9-1.3ubuntu0.1) zesty; urgency=medium
* d/p/dynamic-tcp-backlog.dpatch: Dynamically increase the TCP backlog on
high core-count systems. (LP: #1706735)
-- dann frazier <[email protected]> Mon, 16 Oct 2017 15:37:03
-0600
** Changed in: lmbench (Ubuntu Zesty)
Status: Fix Committed => Fix Released
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https://bugs.launchpad.net/bugs/1706735
Title:
lmbench tcp lib backlog reservation too small, can cause hang.
Status in lmbench package in Ubuntu:
Fix Released
Status in lmbench source package in Xenial:
Fix Committed
Status in lmbench source package in Zesty:
Fix Released
Bug description:
[Impact]
Network related tests will hang on high-core count systems.
lib_tcp reserves backlog of 100. If there are more then 100 threads on
the system, the backlog is pretty much guaranteed to fail. The clients
will then fail to connect and lmbench will hang. Potential patch below
works around this by reserving backlog for at least 4x number of
processors reported in the system, assuming that common use case will
be to run lmbench with as many threads as there are cpus reported from
the OS. Alternatively, backlog reservation can be made into a config
option.
[Test Case]
ubuntu@ubuntu:~$ /usr/lib/lmbench/bin/lat_select -P 128 tcp
connect: Connection timed out
connect: Connection timed out
connect: Connection timed out
connect: Connection timed out
connect: Connection timed out
connect: Connection timed out
connect: Connection timed out
connect: Connection timed out
connect: Connection timed out
connect: Connection timed out
With the patch:
ubuntu@ubuntu:~/lmbench$ /usr/lib/lmbench/bin/lat_select -P 128 tcpSelect on
200 tcp fd's:
XX.XXXX microseconds
[Regression Risk]
The patch is careful to preserve the previous behavior for lower core count
systems. Perhaps if there were a bug in the platform's
sysconf(_SC_NPROCESSORS_ONLN) function, we could end up with a regression that
skewed results.
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