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SMP - using more than one CPU 5 November 2000
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This rather short article is all about adding SMP to your kernel.   Technically, SMP is symmetric multiprocessing.  Practically, it means having more than one CPU.  Such machines are faster than single CPU machines.

In this article, I will assume you have a dual-cpu box.  It's not hard to expand this section to apply to more CPUs, but I'm not going to guess at exactly how that is done.

FreeBSD, by default, does not have SMP enable in the kernel.  This means that FreeBSD sees only the first CPU.  In order to enable the other CPU[s], you need to create a new kernel.  For instructions on how to create a new kernel, refer to the Configuring the FreeBSD Kernel section in the FreeBSD handbook.  Pay special attention to the section on Building and Installing a Custom Kernel.

I created my new kernel, using the above instructions, by searching for SMP within my kernel configuration file.  I found this:

# To make an SMP kernel, the next two are needed
options    SMP          # Symmetric MultiProcessor Kernel
options    APIC_IO      # Symmetric (APIC) I/O

Those are the only options I added to my kernel.  No other changes where made.

For the record, the make took about 8 minutes, I think.  Not sure.  I wasn't timing it properly.

Verifying that SMP is working
Here's what you should see near the end of your dmesg output:
SMP: AP CPU #1 Launched!

That's your second CPU.

Also, if you look at top, you'll see a new column (C), which indicates which CPU a particluar process is running on:

last pid: 171;  load averages:  0.00, 0.00, 0.00 up 0+00:06:32  00:48:30
20 processes:  1 running, 19 sleeping
CPU states: 0.0% user, 0.0% nice, 1.5% system, 0.0% interrupt, 98.5% idle
Mem: 3552K Active, 4556K Inact, 4136K Wired, 8K Cache, 3840K Buf, 47M Free
Swap: 132M Total, 132M Free

 PID USERNAME PRI NICE  SIZE    RES STATE  C   TIME   WCPU    CPU COMMAND
 171 dan       28   0  1856K  1128K CPU0   0   0:00  1.75%  0.24% top
 160 dan       10   0  1012K   808K wait   1   0:00  0.00%  0.00% bash
  80 root       2   0   908K   612K select 0   0:00  0.00%  0.00% syslogd
 159 root       2   0  1216K   904K select 1   0:00  0.00%  0.00% telnetd
 113 root       2   0  1036K   768K select 1   0:00  0.00%  0.00% inetd
 151 root       3   0   920K   636K ttyin  0   0:00  0.00%  0.00% getty
 157 root       3   0   920K   636K ttyin  1   0:00  0.00%  0.00% getty
 156 root       3   0   920K   636K ttyin  0   0:00  0.00%  0.00% getty
 154 root       3   0   920K   636K ttyin  0   0:00  0.00%  0.00% getty
 152 root       3   0   920K   636K ttyin  1   0:00  0.00%  0.00% getty
 153 root       3   0   920K   636K ttyin  1   0:00  0.00%  0.00% getty
 118 root       2   0  1524K  1316K select 1   0:00  0.00%  0.00% sendmail
 158 root       3   0   920K   636K ttyin  0   0:00  0.00%  0.00% getty
 155 root       3   0   920K   636K ttyin  1   0:00  0.00%  0.00% getty
 115 root      10   0   948K   712K nanslp 1   0:00  0.00%  0.00% cron
  83 daemon     2   0   912K   492K select 1   0:00  0.00%  0.00% portmap
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