cpu-policy directives are ignored on FreeBSD/non-Linux platforms(?), falling back to 1 thread

Grep for 'cpu-policy' and 'cpu_detect' in src/ and doc/configuration.txt: Linux topology discovery reads /sys, while the generic path only fetches the total CPU count and leaves one thread. Read the global-section parser and the code that applies the policy to see where it silently no-ops when nbthread is unset. The short-term goal is a fatal config error at parse time pointing at cpu-map; done means 'haproxy -c' fails on FreeBSD or the thread count matches the topology.

Detailed Description of the Problem

The cpu-policy directive (e.g., cpu-policy performance threads-per-core 1) does not work as expected on FreeBSD. Instead of automatically discovering the CPU topology and scaling the threads accordingly, HAProxy falls back to creating only a single thread.

Based on the core developer discussion in GitHub Discussion #2901, automatic CPU topology detection via /sys is currently implemented exclusively for Linux. On FreeBSD and macOS, HAProxy only fetches the total CPU count. However, instead of applying a reasonable thread allocation policy based on the available hardware limits, the parser silently ignores the directive or fails to scale, defaulting to 1 worker thread unless nbthread is explicitly defined.This likely affects all non-Linux platforms (FreeBSD, macOS, OpenBSD, NetBSD).

Expected Behavior

1. Short-term mitigation (Fail-fast validation):Until a proper topology detection mechanism is implemented for this platform, HAProxy should trigger a fatal configuration error during startup or config parsing, such as:

[ALERT] (xxxx) : config : 'cpu-policy' is not implemented on this platform yet, please use 'cpu-map' instead.

2. Ideal long-term solution:Ideally, this feature should function exactly as documented on non-Linux platforms, correctly leveraging the available operating system APIs to detect and utilize all available physical CPU cores.

Steps to Reproduce the Behavior

/usr/local/etc/haproxy.cfg sample:

global
    #nbthread 12
    cpu-policy performance threads-per-core 1
    log /var/run/log local0
    chroot /
    user nobody
    group nobody
    daemon

defaults
    log     global
    mode    http
    timeout connect 5s
    timeout client  50s
    timeout server  50s

frontend https_front
    bind 0.0.0.0:80
    default_backend echo_backend

backend echo_backend
    balance roundrobin
    server backend_server 172.16.0.1:80 id 1 check

haproxy -f /usr/local/etc/haproxy.cfg

Even when generating high multi-threaded load against the load balancer, running top -H confirms that HAProxy utilizes only a single CPU core:

h1load -d 60 -c 200 -t 24 -r 1 -P http://172.160.91:80

Do you have any idea what may have caused this?

No response

Do you have an idea how to solve the issue?

No response

What is your configuration?

Environment:

OS: FreeBSD 15.1-RELEASE-p1 (amd64)
Hardware: AMD Ryzen 9 3900X 12-Core Processor (24 threads with SMT enabled)

% sysctl hw.ncpu hw.model

hw.ncpu: 24
hw.model: AMD Ryzen 9 3900X 12-Core Processor


sysctl -qn kern.sched.topology_spec:

<groups>
 <group level="1" cache-level="0">
  <cpu count="24" mask="ffffff,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0">0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23</cpu>
  <children>
   <group level="2" cache-level="3">
    <cpu count="6" mask="3f,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0">0, 1, 2, 3, 4, 5</cpu>
    <children>
     <group level="3" cache-level="2">
      <cpu count="2" mask="3,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0">0, 1</cpu>
      <flags><flag name="THREAD">THREAD group</flag><flag name="SMT">SMT group</flag></flags>
     </group>
     <group level="3" cache-level="2">
      <cpu count="2" mask="c,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0">2, 3</cpu>
      <flags><flag name="THREAD">THREAD group</flag><flag name="SMT">SMT group</flag></flags>
     </group>
     <group level="3" cache-level="2">
      <cpu count="2" mask="30,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0">4, 5</cpu>
      <flags><flag name="THREAD">THREAD group</flag><flag name="SMT">SMT group</flag></flags>
     </group>
    </children>
   </group>
   <group level="2" cache-level="3">
    <cpu count="6" mask="fc0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0">6, 7, 8, 9, 10, 11</cpu>
    <children>
     <group level="3" cache-level="2">
      <cpu count="2" mask="c0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0">6, 7</cpu>
      <flags><flag name="THREAD">THREAD group</flag><flag name="SMT">SMT group</flag></flags>
     </group>
     <group level="3" cache-level="2">
      <cpu count="2" mask="300,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0">8, 9</cpu>
      <flags><flag name="THREAD">THREAD group</flag><flag name="SMT">SMT group</flag></flags>
     </group>
     <group level="3" cache-level="2">
      <cpu count="2" mask="c00,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0">10, 11</cpu>
      <flags><flag name="THREAD">THREAD group</flag><flag name="SMT">SMT group</flag></flags>
     </group>
    </children>
   </group>
   <group level="2" cache-level="3">
    <cpu count="6" mask="3f000,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0">12, 13, 14, 15, 16, 17</cpu>
    <children>
     <group level="3" cache-level="2">
      <cpu count="2" mask="3000,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0">12, 13</cpu>
      <flags><flag name="THREAD">THREAD group</flag><flag name="SMT">SMT group</flag></flags>
     </group>
     <group level="3" cache-level="2">
      <cpu count="2" mask="c000,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0">14, 15</cpu>
      <flags><flag name="THREAD">THREAD group</flag><flag name="SMT">SMT group</flag></flags>
     </group>
     <group level="3" cache-level="2">
      <cpu count="2" mask="30000,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0">16, 17</cpu>
      <flags><flag name="THREAD">THREAD group</flag><flag name="SMT">SMT group</flag></flags>
     </group>
    </children>
   </group>
   <group level="2" cache-level="3">
    <cpu count="6" mask="fc0000,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0">18, 19, 20, 21, 22, 23</cpu>
    <children>
     <group level="3" cache-level="2">
      <cpu count="2" mask="c0000,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0">18, 19</cpu>
      <flags><flag name="THREAD">THREAD group</flag><flag name="SMT">SMT group</flag></flags>
     </group>
     <group level="3" cache-level="2">
      <cpu count="2" mask="300000,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0">20, 21</cpu>
      <flags><flag name="THREAD">THREAD group</flag><flag name="SMT">SMT group</flag></flags>
     </group>
     <group level="3" cache-level="2">
      <cpu count="2" mask="c00000,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0">22, 23</cpu>
      <flags><flag name="THREAD">THREAD group</flag><flag name="SMT">SMT group</flag></flags>
     </group>
    </children>
   </group>
  </children>
 </group>
</groups>

Output of haproxy -vv

haproxy -vv
HAProxy version 3.4.1-3e888a769 2026/06/25 - https://haproxy.org/
Status: long-term supported branch - will stop receiving fixes around Q2 2031.
Known bugs: http://www.haproxy.org/bugs/bugs-3.4.1.html
Running on: FreeBSD 15.1-RELEASE-p1 FreeBSD 15.1-RELEASE-p1 releng/15.1-0f691888dc56 GENERIC amd64
Build options : 
  TARGET  = freebsd
  CC      = cc
  CFLAGS  = -O2 -g -O2 -pipe -fstack-protector-strong -fno-strict-aliasing -fwrapv -DFREEBSD_PORTS
  OPTIONS = USE_GETADDRINFO=1 USE_OPENSSL=1 USE_ACCEPT4=1 USE_ZLIB=1 USE_CPU_AFFINITY=1 USE_TFO=1 USE_THREAD_DUMP=1 USE_QUIC=1 USE_PROMEX=1 USE_PCRE2=1 USE_PCRE2_JIT=1
  DEBUG   = 

Feature list : -51DEGREES +ACCEPT4 +ACME -BACKTRACE +CLOSEFROM +CPU_AFFINITY -CRYPT_H -DEVICEATLAS -DL -ECH -ENGINE -EPOLL -EVPORTS +GETADDRINFO +KQUEUE -KTLS -LIBATOMIC +LIBCRYPT -LINUX_CAP -LINUX_SPLICE -LINUX_TPROXY -LUA -MATH -MEMORY_PROFILING -NETFILTER -NS -OBSOLETE_LINKER +OPENSSL -OPENSSL_AWSLC -OPENSSL_WOLFSSL -OT -PCRE +PCRE2 +PCRE2_JIT -PCRE_JIT +POLL -PRCTL +PROCCTL +PROMEX -PTHREAD_EMULATION +QUIC -QUIC_OPENSSL_COMPAT -RT -SHM_OPEN -SLZ +SSL -STATIC_PCRE -STATIC_PCRE2 +TFO +THREAD +THREAD_DUMP +TPROXY +TRACE -WURFL +ZLIB
Detected feature list :

Default settings :
  bufsize = 16384, maxrewrite = 1024, maxpollevents = 200

Built with multi-threading support (MAX_TGROUPS=32, MAX_THREADS=1024, default=24).
Built with SSL library version : OpenSSL 3.5.6 7 Apr 2026
Running on SSL library version : OpenSSL 3.5.6 7 Apr 2026
SSL library supports TLS extensions : yes
SSL library supports SNI : yes
SSL library default verify directory : /etc/ssl/certs
SSL library supports : TLSv1.0 TLSv1.1 TLSv1.2 TLSv1.3
OpenSSL providers loaded : default
QUIC: connection sock-per-conn mode support : no
QUIC: GSO emission support : no
Built with the Prometheus exporter as a service
Built with zlib version : 1.3.1
Running on zlib version : 1.3.2
Compression algorithms supported : identity("identity"), deflate("deflate"), raw-deflate("deflate"), gzip("gzip")
Built with transparent proxy support using: IP_BINDANY IPV6_BINDANY
Built with PCRE2 version : 10.47 2025-10-21
PCRE2 library supports JIT : yes
Encrypted password support via crypt(3): yes
Built with clang compiler version 19.1.7 (https://github.com/llvm/llvm-project.git llvmorg-19.1.7-0-gcd708029e0b2)

Available polling systems :
     kqueue : pref=300,  test result OK
       poll : pref=200,  test result OK
     select : pref=150,  test result OK
Total: 3 (3 usable), will use kqueue.

Available multiplexer protocols :
(protocols marked as <default> cannot be specified using 'proto' keyword)
       quic : mode=HTTP  side=FE|BE  mux=QUIC  flags=HTX|NO_UPG|FRAMED
       qmux : mode=HTTP  side=FE|BE  mux=QMUX  flags=HTX|NO_UPG
         h2 : mode=HTTP  side=FE|BE  mux=H2    flags=HTX|HOL_RISK|NO_UPG
         h1 : mode=HTTP  side=FE|BE  mux=H1    flags=HTX|NO_UPG
  <default> : mode=HTTP  side=FE|BE  mux=H1    flags=HTX
       fcgi : mode=HTTP  side=BE     mux=FCGI  flags=HTX|HOL_RISK|NO_UPG
       spop : mode=SPOP  side=BE     mux=SPOP  flags=HOL_RISK|NO_UPG
  <default> : mode=SPOP  side=BE     mux=SPOP  flags=HOL_RISK|NO_UPG
       none : mode=TCP   side=FE|BE  mux=PASS  flags=NO_UPG
  <default> : mode=TCP   side=FE|BE  mux=PASS  flags=

Available services : prometheus-exporter
Available filters :
        [BWLIM] bwlim-in
        [BWLIM] bwlim-out
        [CACHE] cache
        [COMP] comp-req
        [COMP] comp-res
        [COMP] compression
        [FCGI] fcgi-app
        [SPOE] spoe
        [TRACE] trace

Last Outputs and Backtraces

Additional Information

No response