[Bug 233395] In FreeBSD 11.x contigfree takes too much time on Xeon Gold 5115 CPU

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=233395

            Bug ID: 233395
           Summary: In FreeBSD 11.x contigfree takes too much time on Xeon
                    Gold 5115 CPU
           Product: Base System
           Version: 11.2-STABLE
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: bugs at FreeBSD.org
          Reporter: steevanxperia at gmail.com

Created attachment 199442
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=199442&action=edit
Contains simple kernel module source and a makefile

Hi

I am seeing a FreeBSD 11.x OS poor performance issue on Xeon Gold CPU.
CPU is Intel(R) Xeon(R) Gold 5115 CPU @ 2.40GHz ( dual socket CPU with 10 cores
per socket )

I have attached a simple kernel module program ( for FreeBSD) and its Makefile.
This just allocates  32KB contiguous memory using contigmalloc and then frees
it using contigfree.
This repeated 1000 times and time taken by contigmalloc and contigfree is
computed .

I can see that contigfree takes way too much time .

I have another older server running FreeBSD 11.2   Intel(R) Xeon(R) CPU E5-2620
v2 @ 2.10GHz  (dual socket 6 core per socket and in this I do not see such an
issue .

Any idea why contigfree takes so much time on FreeBSD 11.x running on Xeon Gold
5115 CPU ?

It looks like this issue affects only the systems which have more than 16
physical CPU cores.

Because of this issue the driver for our PCIe card takes more than 2 minutes to
load and upto 15 minutes to unload. 

System and CPU details: 
CPU: Intel(R) Xeon(R) Gold 5115 CPU @ 2.40GHz (2400.07-MHz K8-class CPU)
FreeBSD/SMP: Multiprocessor System Detected: 40 CPUs

System Information
    Manufacturer: Supermicro
    Product Name: Super Server
    Version: 0123456789
Base Board Information
    Manufacturer: Supermicro
    Product Name: X11DPH-Tq
    Version: 1.01

Regards,
Steevan

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