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I've found such option on my server:

ACPI SLIT Preferences NOTE: This option is available on Gen8 servers with Intel processors. ACPI SLIT (System Locality Information Table) describes the relative access times between processors,memory subsystems, and I/O subsystems. Operating systems that support SLIT can improve performance by allocating resources and workloads more efficiently.Options include:

  • Enable
  • Disable (default)

Sounds cool, but I wonder why it disabled by default? More or less I understand advantages of turning it on, but what is disadvantages of turning it on?

Oleg Vazhnev
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  • There are very few Operating Systems that support this. As far as I know only some special versions of Linux geared towards use in large clusters have support for this. Solaris and VMWare Esx 5 maybe too, but I'm not sure of that. So normally you won't get any benefit from this. – Tonny May 18 '13 at 09:07

1 Answers1

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The same applies to virtualization related settings (VT-x, Vanderpool).
As far as I know ALL hardware manufacturers disable such features by default as a matter of principle.

Why ? Good question.
Normally an OS that doesn't support or need the feature won't be bothered by it, if it is on.
(At least I have never encountered such a case myself and I have never heard of this happening either.)

As far as I know this appears some sort of (legal) safety measure by the manufactures, driven by the fear for costly lawsuits.
After all: most manufacturers have a legal entity in lawsuit happy USA jurisdictions...
"If it is off, it can't cause problems, so we can't be liable for anything..."

Tonny
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  • Less code/complexity is nearly always more reliable and easier to support than more code/complexity. – Rob Moir May 18 '13 at 09:52
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    @RobM That's not the point: The code is already there. Just not enabled by default. When it is enabled (but not used by the OS) it makes no difference for the support/complexity. – Tonny May 18 '13 at 10:42
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    If it's not enabled then its not part of the support burden of troubleshooting a fault on that platform. If I install Windows or Linux server on that hardware and start seeing problems with the server crashing then while that setting is disabled then that's one thing that *isn't* part of the problem. It *does* make a difference. – Rob Moir May 18 '13 at 12:51
  • @RobM From that perspective you are right. But on a normal working system it doesn't make a difference. – Tonny May 18 '13 at 18:01
  • You don't *know* that for sure. Neither do I. And if its not used by the majority of systems (as you yourself say) then it makes sense not to enable it by default because any intrusion it could possibly have onto a system that doesn't support it is likely to be negative. – Rob Moir May 18 '13 at 19:02
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    why do you think that this options is not supported by regular Windows/Linux? In this guide http://h20000.www2.hp.com/bc/docs/support/SupportManual/c01804533/c01804533.pdf it's suggested to TURN ON this option, and guide is written regarding regular Windows/Linux builds. – Oleg Vazhnev May 19 '13 at 06:59
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    @javapowered I'm well aware of that whitepaper, and also the various documents that it refers to. Current Linux and Windows versions still use NUMA for these optimizations. SLIT works in concert with NUMA, but only if the NUMA core in the OS kernel knows how to use it. This is NOT the case for Windows 2012 (is expected for the next kernel update, according to the MS developers I spoke to in January when I was in Redmond). Linux requires a special kernel with (experimental) patches. I also have tested 2012 on HP G8 and Dell servers myself without observing any difference with this on or off. – Tonny May 19 '13 at 09:46
  • Thanks Tonny, still strange for me that HP doesn't mention this important information in the guide, but I will disable this option because I don't want to introduce hard-to-diagnose problems. – Oleg Vazhnev May 19 '13 at 20:09
  • @javapowered That's probably best for now. It will be interesting to see what the next iteration of both Window sand Linux will bring. Windows support ought to be in 8.1 (Blue), which is expected fall this year. Linux support is already in the 3.10 kernels or should be there soon (I have not quite kept up to date the last couple of months, so I don't know the exact status.) – Tonny May 19 '13 at 20:31