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docs: DPDK Linux kernel underruns solution

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Previously we had documented a known issue involving the Linux kernel,
which was causing a streaming performance regression. This resulted in
periodic underruns. We now know what is causing the regression. Document
the procedure to restore the original behavior.

Signed-off-by: mattprost <matt.prost@ni.com>
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mattprost 2022-06-20 14:37:20 -05:00 committed by Aaron Rossetto
parent b584a7a923
commit e93377b053
1 changed files with 21 additions and 5 deletions
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@ -227,12 +227,28 @@ arguments, where N is the desired timeout time in <b>milliseconds</b>, or
by adding a `dpdk_link_timeout` entry to the
\ref page_configfiles "UHD configuration file".
\subsection dpdk_notes DPDK performance dpdk_notes
\subsection dpdk_troubleshooting Troubleshooting
With Linux kernel 5.11 on Ubuntu 20.04, we have observed periodic underruns
on systems that otherwise have no issues. The behavior does not reproduce on
the 5.4 kernel that is also available for Ubuntu 20.04, so that version can
be used as a workaround.
With Linux kernels 5.10 and beyond, we have observed periodic underruns on systems
that otherwise have no issues. These Linux kernel versions are the default for Ubuntu
20.04.3 LTS and later. The underrun issue is due to the RT_RUNTIME_SHARE feature
being disabled by default in newer versions of the Linux kernel. The following
procedure can be used to enable RT_RUNTIME_SHARE. Note, this process was tested on
Linux kernel version 5.13. The procedure may be slightly different on other kernel
versions. To determine the Linux kernel version of your system, in a terminal issue
the command `uname -r`.
sudo -s
cd /sys/kernel/debug/sched/
cat features
GENTLE_FAIR_SLEEPERS START_DEBIT NO_NEXT_BUDDY LAST_BUDDY CACHE_HOT_BUDDY WAKEUP_PREEMPTION NO_HRTICK NO_HRTICK_DL NO_DOUBLE_TICK NONTASK_CAPACITY TTWU_QUEUE SIS_PROP NO_WARN_DOUBLE_CLOCK RT_PUSH_IPI **NO_RT_RUNTIME_SHARE** NO_LB_MIN ATTACH_AGE_LOAD WA_IDLE WA_WEIGHT WA_BIAS UTIL_EST UTIL_EST_FASTUP NO_LATENCY_WARN ALT_PERIOD BASE_SLICE
echo RT_RUNTIME_SHARE > features
cat features
GENTLE_FAIR_SLEEPERS START_DEBIT NO_NEXT_BUDDY LAST_BUDDY CACHE_HOT_BUDDY WAKEUP_PREEMPTION NO_HRTICK NO_HRTICK_DL NO_DOUBLE_TICK NONTASK_CAPACITY TTWU_QUEUE SIS_PROP NO_WARN_DOUBLE_CLOCK RT_PUSH_IPI **RT_RUNTIME_SHARE** NO_LB_MIN ATTACH_AGE_LOAD WA_IDLE WA_WEIGHT WA_BIAS UTIL_EST UTIL_EST_FASTUP NO_LATENCY_WARN ALT_PERIOD BASE_SLICE
*/
// vim:ft=doxygen: