Sandybridge Scalability with 3 & 4 cores

Matthew Tippett matthew at
Thu Feb 17 16:23:52 UTC 2011

Thanks Kris,

Moving to freebsd-performance.

Hi all,

When running NASA's NAS Parallel Benchmarks [1] under Phoronix Test 
Suite [2] on PC-BSD 8.1, we are seeing a scalability issue on Intel's 
new Sandybridge hardware.

We see scalability at 1, 2 and 6 processors enabled (via BIOS).  At 3 & 
4 cores, we're seeing drop off in some tests, or a collapse in 
performance in others.  Although it may be a quirk on the Sandybridge 
hardware, it may also be a scalability issue in general.

Attached are two images showing the collapse in scalability.  The LU.A 
test was unable to complete in a reasonable time (hours, vs the expected 
minutes) and was aborted.  Interestingly the scalability at 6 cores were 
in line with the other platforms.

To repeat these tests, you can download Phoronix Test Suite 3 RC and run 
the NAS Parallel Benchmarks via the command

       ./phoronix-test-suite benchmark pts/npb

And choose either the MG.B or LU.A subtest.  We'll be trying to remove 
the HW from being a potential factor.

Also note that scalability of 6 cores + HyperThreading also dropped off 
fairly heavily (so did OpenIndiana).

Thanks in advance.



On 02/14/2011 06:16 AM, Kris Moore wrote:
> Hash: SHA1
> On 02/14/2011 02:09, Matthew Tippett wrote:
>> Hi Kris,
>> I work with Michael Larabel, of Phoronix fame.  We've recently run some
>> benchmarks with a core i7 970 against OpenIndiana,  PC-BSD and Ubuntu
>> with various cores turned off.
>> One interesting behaviour that we saw is that between 3 and 4 cores
>> running the performance of PC-BSD dropped fairly badly in some of the
>> NAS parallel benchmarks.  The system performs reasonably well for 1,2
>> and 6 cores.   Is this performance behaviour known within the PC-BSD
>> community?  It is fairly easy to reproduce the results with the Phoronix
>> Test Suite and we'd be happy to work with some developers in determining
>> the underlying issue.
>> Note, however that the article covering this benchmark will probably get
>> published over the next few days.
>> Regards,
>> Matthew
> Matthew,
> Thanks for the heads up! What specific types of benchmarks are falling
> behind? On the PC-BSD side we mostly handle usability stuff, and don't
> monkey with the FreeBSD internals, so this may best be a question for
> the FreeBSD Performance mailing list. I'm sure you'll get all kinds of
> comments there on how to improve the scalability tuning, and if there is
> still an issue then those will be the people who can fix it :)
> - --
> Kris Moore
> PC-BSD Software
> iXsystems
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