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Bug 2050244 - cyclictest: Ignore inherited affinity when applying new affinity
Summary: cyclictest: Ignore inherited affinity when applying new affinity
Keywords:
Status: CLOSED ERRATA
Alias: None
Deadline: 2022-02-14
Product: Red Hat Enterprise Linux 9
Classification: Red Hat
Component: realtime-tests
Version: 9.0
Hardware: Unspecified
OS: Unspecified
high
unspecified
Target Milestone: rc
: ---
Assignee: John Kacur
QA Contact: Mike Stowell
URL:
Whiteboard:
Depends On:
Blocks: 1983783
TreeView+ depends on / blocked
 
Reported: 2022-02-03 14:24 UTC by John Kacur
Modified: 2022-05-17 13:34 UTC (History)
2 users (show)

Fixed In Version: realtime-tests-2.3-2.el9
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Environment:
Last Closed: 2022-05-17 13:22:25 UTC
Type: Bug
Target Upstream Version:
Embargoed:
pm-rhel: mirror+

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Red Hat Issue Tracker RHELPLAN-111002 0 None None None 2022-02-03 14:26:55 UTC
Red Hat Product Errata RHBA-2022:2498 0 None None None 2022-05-17 13:22:33 UTC

Description John Kacur 2022-02-03 14:24:55 UTC 
This bug was initially created as a copy of Bug #2050242

Description of problem:

If a new affinity is requested we currently calculate a cpumask that is the intersection of the set of the newly requested affinity and the runtime or inherited cpumask.

While this makes sense in some circumstances, such as if the requester wants to add '+' or take away '!' from the current set.

This doesn't make sense if a new affinity is requested and is too restrictive. It can result in no cpus being available for example when isolcpus has been applied.
Comment 2 John Kacur 2022-02-03 15:28:51 UTC 
How to Test:

You can use taskset to set the runtime environment that cyclictest will inherit, and then use the -a flag to alter it in cyclictest.
For example
Before this change
taskset --cpu-list 0-4,8 ./cyclictest -t -a 0,3-6
# /dev/cpu_dma_latency set to 0us
policy: other/other: loadavg: 2.26 2.23 2.52 4/2349 16998           

T: 0 (16262) P: 0 I:1000 C: 550911 Min:      3 Act:   52 Avg:   61 Max:   26423
T: 1 (16263) P: 0 I:1500 C: 362514 Min:      3 Act:   52 Avg:   83 Max:   27363
T: 2 (16264) P: 0 I:2000 C: 273451 Min:      3 Act:   52 Avg:   82 Max:   28608

The runtime environment consists of cpus 0,1,2,3,4,8
the requested affinity includes cpus 0,3,4,5,6
The Intersection of those cpus is 0,3,4 - so therefore we get just 3 threads as you can see above.
You can also use taskset -p pid, to examine the cpumasks but this is a bit complicated for the purpose here and not necessary.

After the change we get
taskset --cpu-list 0-4,8 ./cyclictest -t -a 0,3-6
# /dev/cpu_dma_latency set to 0us
policy: other/other: loadavg: 2.48 2.30 2.54 1/2351 17291           

T: 0 (17286) P: 0 I:1000 C:   3985 Min:      4 Act:   52 Avg:   58 Max:    1818
T: 1 (17287) P: 0 I:1500 C:   2643 Min:      5 Act:   52 Avg:   68 Max:   13469
T: 2 (17288) P: 0 I:2000 C:   1991 Min:      6 Act:   53 Avg:   59 Max:    3206
T: 3 (17289) P: 0 I:2500 C:   1592 Min:      7 Act:   53 Avg:   56 Max:    2521
T: 4 (17290) P: 0 I:3000 C:   1329 Min:      6 Act:   53 Avg:   69 Max:    2766

So the requested affinity includes cpus 0,3,4,5,6 or 5 threads which is what we see above.
Comment 9 errata-xmlrpc 2022-05-17 13:22:25 UTC 
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 (new packages: realtime-tests), 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://access.redhat.com/errata/RHBA-2022:2498
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