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Bug 1344077 - turn CONFIG_RCU_NOCB_CPU_ALL=y off
turn CONFIG_RCU_NOCB_CPU_ALL=y off
Status: CLOSED ERRATA
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: kernel-rt (Show other bugs)
7.3
x86_64 Linux
medium Severity high
: rc
: ---
Assigned To: Clark Williams
Jiri Kastner
: ZStream
Depends On:
Blocks: 1274397 1348715 1349770
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Reported: 2016-06-08 13:02 EDT by Daniel Bristot de Oliveira
Modified: 2016-11-03 15:52 EDT (History)
2 users (show)

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: 1348715 1349770 (view as bug list)
Environment:
Last Closed: 2016-11-03 15:52:58 EDT
Type: Bug
Regression: ---
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External Trackers
Tracker ID Priority Status Summary Last Updated
Red Hat Product Errata RHSA-2016:2584 normal SHIPPED_LIVE Important: kernel-rt security, bug fix, and enhancement update 2016-11-03 08:08:49 EDT

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Description Daniel Bristot de Oliveira 2016-06-08 13:02:02 EDT 
Description of problem:

Although rcu no callbacks is useful for the majority of -rt workloads. There are cases where this feature can cause bad impact in the -rt performance.

For example, if the rcuc/ thread needs to wake up many offload threads, for instance in a large box with dozens CPUs, this can cause an interface that can be higher than the 150 microseconds we guarantee in the -rt products.

As we can enable the rcu no callbacks via kernel command line, we still can have the same behavior of CONFIG_RCU_NOCB_CPU_ALL=y by using the rcu_nocbs=<allcpus>. So it is safe to turn it off. In fact, this gives us more flexibility than have all CPUs rcu_nocbs by default
Comment 1 Clark Williams 2016-06-23 14:58:03 EDT 
This change was made in:

kernel-rt-3.10.0-439.rt56.327.el7
Comment 7 errata-xmlrpc 2016-11-03 15:52:58 EDT 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHSA-2016-2584.html
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