kern/109936: SMP kernel performance problem on FSC TX600

Ludger Bolmerg lbolmerg at
Mon Mar 5 18:20:04 UTC 2007

>Number:         109936
>Category:       kern
>Synopsis:       SMP kernel performance problem on FSC TX600
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    freebsd-bugs
>State:          open
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Mon Mar 05 18:20:03 GMT 2007
>Originator:     Ludger Bolmerg
>Release:        6.2
FreeBSD 6.2-RELEASE-p2 FreeBSD 6.2-RELEASE-p2 #1
I installed FreeBSD 6.2 on a Fujitsu Siemens TX600 S3 with 2 dual core Xeon processors and 4G RAM.
Here is the link to the data sheet of the server on Fujitsu-Siemens' Web page.  It may be helpful

The SMP kernel is awfully slow.  make buildkernel takes about 6 hours to complete.  When I boot a UP kernel the build completes within 12 minutes.  I don't see any unusual message in any log file.

Booting the SMP kernel with kern.smp.disabled=1 shows good performance values.

When booting the SMP kernel with 


also results in good performance.  Disabling single CPUs didn't work. I had to apply a patch provided by John Baldwin.

Disabling all but one CPU also gives good performance. As soon as the second CPU gets enabled it becomes slow again.

Install on same hardware


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