Sandybridge Scalability with 3 & 4 cores
matthew at phoronix.com
Thu Feb 17 16:23:52 UTC 2011
Moving to freebsd-performance.
When running NASA's NAS Parallel Benchmarks  under Phoronix Test
Suite  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:
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> 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.
> 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
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