AMD's memory controllers are fine

Article: Bulldozer Benchmarks, What Do They Mean?
By: Vincent Diepeveen (diep.delete@this.xs4all.nl), April 7, 2011 2:15 pm
Room: Moderated Discussions
anon (anon@anon.com) on 4/6/11 wrote:
---------------------------
>Vincent Diepeveen (diep@xs4all.nl) on 4/6/11 wrote:
>---------------------------
>>anon (anon@anon.com) on 4/5/11 wrote:
>>---------------------------
>>>anon (anon@anons.com) on 4/5/11 wrote:
>>>---------------------------
>>>>>There is no reason to believe that AMD will have problems with their memory controllers
>>>>>in production silicon. It's either mis-configured or some sort of early bug that will get fixed.
>>>>>
>>>>
>>>>There're whole lot more ways to screw up memory subsystem
>>>>performance than improving it.
>>>>
>>>>Just ask Nehalem-EX team.
>>>
>>>How so?
>>
>>Has ugly latency to RAM when doing random lookups through machine. This where 2
>>socket chip and the i7-980 and sisters of it really have great latency to RAM.
>
>Can you use some standard terminolgy please?
>
>When you say random lookups through machine, do you mean random remote memory loads?
>What is the ugly latency in that case, compared with other systems without ugly latency?

Simply the test i wrote you can run and see for yourself. If you drop a mail with your email adress i'll email it to you, and you can toy with it yourself.

What happens in reality in all modern software that requires big shared memory hardware is that different threads or processes (on paper the same thing) cooperate with each other. So they communicate with each other or write into a big ram size and read a lot from the huge RAM size.

This goes crisscross through the RAM and of course all cores undertake at the same time these actions.

If you wouldn't do this, but ideally stream things, you don't need such an expensive box of $205k+ but can do with a few second hand Q6600 for each $250 and connect them with an old router and a few second hand patch cables, or when not needing RAM at all you can easily do with a GPU streaming and number crunching.

So for the software that's not working so easily onto a GPU nor a cheapo cluster, it makes sense to use the strong point of a multicore box and that's doing random reads from all cores to all cores using a huge RAM buffer.

That makes sense.

The barcelona box i have here, which i built for 1000 euro second hand, was not exactly good in that. It requires roughly 300 ns for random lookups throughout the machine.
Clocked 2.3Ghz.

Some high clocked 2 socket nehalems with in total 12 real cores and of course SMT turned off, using expensive RAM, will get you to the 90 ns range.

i7 achieves 70 ns there.

phenom ddr3 achieves 90-100 ns there and phenom ddr2 achieves 115-125 ns there.

Nehalem-Ex falls however in the barcelona league there.

Now whatever causes this, and i sure am aware of some factors, to users it is not useful.

They simply benchmark their software and ugh out so won't pay that huge extra price a multisocket box eats.

The 2 socket Nehalem with little cores, a max of 6, really is doing great here, yet latencies in the hundreds of nanoseconds really is from previous decade, yet that's what Nehalem-ex shows.

Now this might be a result of spec just doing things in a throughput manner, yet that's not what companies pay that huge price for when ordering a box.

Not the average time to completion matters. Speedup of your application matters. If communication between threads gets slowed down by slower latencies, that will be a decisive factor to not buy it.

>>
>>Now all that would be ok for nehalem-ex if price was ok, but it isn't.
>>
>>The only reason it will sell is because it has intel sticker at it, no other reasons.
>
>Its oltp numbers are pretty good.


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New article: Bulldozer benchmark analysisDavid Kanter2011/03/30 02:27 AM
  New article: Bulldozer benchmark analysisNaN2011/03/30 07:47 AM
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                  Post removedDavid Kanter2011/04/02 12:39 PM
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                                                    Sorry again, Brendan (NT)Michael S2011/04/20 10:43 AM
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                                                                            File size optimizationsRicardo B2011/04/25 08:22 AM
                                                                              ContinuationRicardo B2011/04/25 08:25 AM
                                                                              File size optimizationsChristian Packmann2011/04/25 09:56 AM
                                                                                File size optimizationsEduardoS2011/04/25 11:57 AM
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                                                                            File size optimizationsjrl2011/04/25 05:54 PM
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                                                                          File size optimizationsHeath Provost2011/04/25 02:02 PM
                                    Imperative compilers (and the lack of it)Azazel2011/04/12 08:23 PM
                                Imperative compilers (and the lack of it)none2011/04/10 06:00 AM
                                  Imperative compilers (and the lack of it)dmsc2011/04/10 06:39 AM
                                  Imperative compilers (and the lack of it)EduardoS2011/04/10 12:55 PM
                                compiler failure rateshobold2011/04/10 10:55 AM
                                  compiler failure rates?2011/04/10 11:13 PM
                                    compiler failure rateshobold2011/04/11 05:07 AM
                                Imperative compilers (and the lack of it)EduardoS2011/04/10 12:55 PM
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                                    Imperative compilers (and the lack of it)Konrad Schwarz2011/04/14 01:28 AM
                                      Imperative compilers (and the lack of it)gallier22011/04/14 04:47 AM
                                      Imperative compilers (and the lack of it)EduardoS2011/04/14 02:04 PM
                                        Imperative compilers (and the lack of it)Konrad Schwarz2011/04/15 03:43 AM
                                Hard register problemsRob Thorpe2011/04/11 12:14 AM
                                  Hard register problemsMax2011/04/11 03:05 PM
                                    Hard register problemsRob Thorpe2011/04/11 03:28 PM
                                Imperative compilers (and the lack of it)gallier22011/04/11 09:26 AM
                                  I wonder why.j2011/04/11 10:39 PM
                                    I wonder why.?2011/04/11 11:44 PM
                                Imperative compilers (and the lack of it)nksingh2011/04/12 11:00 PM
                                  Imperative compilers (and the lack of it)?2011/04/12 11:23 PM
                              AMD's Open64 compiler ?Vincent Diepeveen2011/04/10 06:06 AM
                                AMD's Open64 compiler ?none2011/04/10 07:23 AM
                                  AMD's Open64 compiler ?Eugene Nalimov2011/04/11 03:57 PM
                                    AMD's Open64 compiler ?EduardoS2011/04/12 02:55 PM
                                AMD's Open64 compiler ?Megol2011/04/10 11:05 PM
                                  AMD's Open64 compiler ?Vincent Diepeveen2011/04/20 12:52 PM
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                    AMD's Open64 compiler ?Vincent Diepeveen2011/04/05 12:02 PM
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        AMD's memory controllers are fineDavid Kanter2011/03/31 09:27 AM
          AMD's memory controllers are fineanon2011/04/05 11:24 AM
            AMD's memory controllers are fineanon2011/04/05 04:52 PM
              AMD's memory controllers are fineVincent Diepeveen2011/04/06 01:36 AM
                AMD's memory controllers are fineanon2011/04/06 06:59 AM
                  AMD's memory controllers are fineVincent Diepeveen2011/04/07 02:15 PM
                    AMD's memory controllers are fineVincent Diepeveen2011/04/07 02:27 PM
                      AMD's memory controllers are fineanon2011/04/07 02:57 PM
                    AMD's memory controllers are fineanon2011/04/07 02:54 PM
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  a waste of timeMoritz2011/04/09 07:01 AM
    a waste of timehorsefly2011/04/09 03:34 PM
      a waste of timeDavid Kanter2011/04/09 06:56 PM
        a waste of timehorsefly2011/04/10 05:13 AM
          InvestorsDavid Kanter2011/04/10 06:27 AM
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