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Bug 1875275 - Failure to enter full_nohz due to needless SCHED softirqs
Summary: Failure to enter full_nohz due to needless SCHED softirqs
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 8
Classification: Red Hat
Component: kernel-rt
Version: 8.4
Hardware: Unspecified
OS: Unspecified
unspecified
unspecified
Target Milestone: rc
: 8.0
Assignee: Juri Lelli
QA Contact: Qiao Zhao
URL:
Whiteboard:
Depends On:
Blocks: 1990272 1990273
TreeView+ depends on / blocked
 
Reported: 2020-09-03 07:58 UTC by Juri Lelli
Modified: 2021-11-09 18:31 UTC (History)
12 users (show)

Fixed In Version: kernel-rt-4.18.0-326.rt7.107.el8
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
: 1990272 1990273 (view as bug list)
Environment:
Last Closed: 2021-11-09 17:28:30 UTC
Type: Bug
Target Upstream Version:
Embargoed:


Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Gitlab redhat/rhel/src/kernel rhel-8 merge_requests 928 0 None None None 2021-07-06 14:48:55 UTC
Red Hat Product Errata RHSA-2021:4140 0 None None None 2021-11-09 17:29:31 UTC

Description Juri Lelli 2020-09-03 07:58:17 UTC
Description of problem:
Running sysjitter workload on a system running with tuned cpu-partitioning
profile results in an excessive number of interrupts.

Debugging performed in bz1833196 resulted in a set of patches to reduce
perturbation from timers, however it also highlighted that we still need
to fix an additional case related to the scheduler use of SD_LOAD_BALANCE
flag (bz1833196#c38).

This is to track resolution of the remaining issue, either backporting
upstream patches that removes SD_LOAD_BALANCE flag or the RHEL only fix
proposed in the bz above (bz1833196#c48).

Steps to Reproduce:
1. install perf and sysjitter (https://github.com/alexeiz/sysjitter)
2. start cpu-partitioning profile with isolated and nonbalance cpus
3. perf stat -C 4 -e irq_vectors:local_timer_entry taskset --cpu-list 4 ./sysjitter/sysjitter --runtime 10 200 (on an isolated/non balance cpu)

Actual results:
Very high number (thousand) of irq_vectors:local_timer_entry events, e.g.

[root@rt-qe-04 ~]# perf stat -C 4 -e irq_vectors:local_timer_entry taskset --cpu-list 4 ./sysjitter/sysjitter --runtime 10 200
core_i: 4
threshold(ns): 200
cpu_mhz: 2398
runtime(ns): 9995739030
runtime(s): 9.996
int_n: 10005
int_n_per_sec: 1000.927
int_min(ns): 2760
int_median(ns): 6025
int_mean(ns): 6056
int_90(ns): 6086
int_99(ns): 6685
int_999(ns): 6775
int_9999(ns): 8123
int_99999(ns): 12657
int_max(ns): 12657
int_total(ns): 60598000
int_total(%): 0.606

 Performance counter stats for 'CPU(s) 4':

            11,007      irq_vectors:local_timer_entry

Expected results:
Very low number (double digit) of irq_vectors:local_timer_entry events

[root@rt-qe-04 ~]# perf stat -C 4 -e irq_vectors:local_timer_entry taskset --cpu-list 4 ./sysjitter/sysjitter --runtime 10 200
core_i: 4
threshold(ns): 200
cpu_mhz: 2398
runtime(ns): 9995639269
runtime(s): 9.996
int_n: 4
int_n_per_sec: 0.400
int_min(ns): 2807
int_median(ns): 6078
int_mean(ns): 5721
int_90(ns): 10602
int_99(ns): 10602
int_999(ns): 10602
int_9999(ns): 10602
int_99999(ns): 10602
int_max(ns): 10602
int_total(ns): 22887
int_total(%): 0.000

 Performance counter stats for 'CPU(s) 4':

                42      irq_vectors:local_timer_entry

Comment 26 errata-xmlrpc 2021-11-09 17:28:30 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 (Moderate: kernel-rt security and bug fix update), 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/RHSA-2021:4140


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