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Date:      Thu, 09 Jan 2020 11:00:00 +0000
From:      bugzilla-noreply@freebsd.org
To:        bugs@FreeBSD.org
Subject:   [Bug 243212] High CPU usage when set affinity on multiple CPU
Message-ID:  <bug-243212-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D243212

            Bug ID: 243212
           Summary: High CPU usage when set affinity on multiple CPU
           Product: Base System
           Version: 12.1-RELEASE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: pizzamig@freebsd.org

We are facing a minor, but disturbing regression, when we moved from FreeBSD
11.3 to 12.1 on our loadbalancers.

We have 2 identical machines (dual CPU, 4 core per CPU), one running FreeBSD
11.3 and one running 12.1.=20
Identical packages and identical configuration.

We have a haproxy instance and, for performance reasons, we pin the threads=
 to
different cpus:
  nbproc 1
  nbthread 6
  cpu-map auto:1/1-6 0-5

The result of this configuration is (on 11.3):
# cpuset -g -p 35799
pid 35799 mask: 0, 1, 2, 3, 4, 5

while on 12.1 is:
# cpuset -g -p 86498
pid 86498 mask: 0, 1, 2, 3, 4, 5
pid 86498 domain policy: first-touch mask: 0, 1

What we have seen is a increased CPU usage (2x) and system load (almost
doubled) on FreeBSD 12.1. We didn't measure a potential impact on the netwo=
rk
latency.
A way to solve/workaround the issue is to decrease the number of threads to=
 4.

I guess that this regression has something to do with NUMA, maybe threads 4=
,5
are forced to use memory domain 0, causing the additional CPU usage.

Is this intended? If yes, why on FreeBSD 11.3 we don't see this high CPU us=
age?
Thanks in advance for the help

I report here some hardware information.

hw.model: Intel(R) Xeon(R) CPU E5-2643 0 @ 3.30GHz
hw.ncpu: 8
kern.sched.topology_spec: <groups>
 <group level=3D"1" cache-level=3D"0">
  <cpu count=3D"8" mask=3D"ff,0,0,0">0, 1, 2, 3, 4, 5, 6, 7</cpu>
  <children>
   <group level=3D"2" cache-level=3D"3">
    <cpu count=3D"4" mask=3D"f,0,0,0">0, 1, 2, 3</cpu>
    <children>
     <group level=3D"3" cache-level=3D"2">
      <cpu count=3D"1" mask=3D"1,0,0,0">0</cpu>
     </group>
     <group level=3D"3" cache-level=3D"2">
      <cpu count=3D"1" mask=3D"2,0,0,0">1</cpu>
     </group>
     <group level=3D"3" cache-level=3D"2">
      <cpu count=3D"1" mask=3D"4,0,0,0">2</cpu>
     </group>
     <group level=3D"3" cache-level=3D"2">
      <cpu count=3D"1" mask=3D"8,0,0,0">3</cpu>
     </group>
    </children>
   </group>
   <group level=3D"2" cache-level=3D"3">
    <cpu count=3D"4" mask=3D"f0,0,0,0">4, 5, 6, 7</cpu>
    <children>
     <group level=3D"3" cache-level=3D"2">
      <cpu count=3D"1" mask=3D"10,0,0,0">4</cpu>
     </group>
     <group level=3D"3" cache-level=3D"2">
      <cpu count=3D"1" mask=3D"20,0,0,0">5</cpu>
     </group>
     <group level=3D"3" cache-level=3D"2">
      <cpu count=3D"1" mask=3D"40,0,0,0">6</cpu>
     </group>
     <group level=3D"3" cache-level=3D"2">
      <cpu count=3D"1" mask=3D"80,0,0,0">7</cpu>
     </group>
    </children>
   </group>
  </children>
 </group>
</groups>

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