IDS Forum

Re: Multiprocessor setting

Posted By: Richard Snoke
Date: Thursday, 22 July 2010, at 3:12 p.m.

In Response To: Re: Multiprocessor setting (Art Kagel)

Hi Art,

I agree with your comments. My only point about the upper bound is that
if you really only need 4-6 CPU VPs and configure 24, that's overkill. I
prefer to work by adding VPs until the response times are acceptable, then
add a couple extra. I agree, you do need to know when you've gone as far
as a particular system can go. No need to continue that particular
debate.

Cheers,
Dick Snoke
IBM ChannelWorks

dsnoke@us.ibm.com
(404) 487-1595

From: "Art Kagel" <art.kagel@gmail.com>
To: ids@iiug.org
Date: 07/22/2010 02:47 PM
Subject: Re: Multiprocessor setting [20629]
Sent by: ids-bounces@iiug.org

Dick,

I agree on several points. If you have only two CPUs/cores whatever, and a

single CPU VP, then you may be OK setting MULTIPROCESSOR to zero and I can

see where there might be some performance improvement over a single CPU VP

with MULTIPROCESSOR set to 1.

I also agree that on current systems it's a moot point since most machines

today have more than 2 cores per slot and most have two or more CPU slots
filled.

I also love your rule of thumb based on pi! ;-)

But the point about only configuring as many CPU VPs as you need for your
workload is specious. Workloads change. If you don't know how many CPU VPs

you can safely configure on a given set of hardware and still see
incremental gains in either per session performance or overall throughput
of
the system, then you can't know what to do when your workload increases as

it will inevitably do. So, on one face this part of the discussion should
be a purely philosophical discussion to determine where that limit is so
that when we come to the other face of the discussion and we are running
out
of steam, we know whether to add a CPU VP or to order another CPU card or
an
upgraded server.

Art

Art S. Kagel
Advanced DataTools (www.advancedatatools.com)
IIUG Board of Directors (art@iiug.org)

Disclaimer: Please keep in mind that my own opinions are my own opinions
and
do not reflect on my employer, Advanced DataTools, the IIUG, nor any other

organization with which I am associated either explicitly, implicitly, or
by
inference. Neither do those opinions reflect those of other individuals
affiliated with any entity with which I am affiliated nor those of the
entities themselves.

On Thu, Jul 22, 2010 at 2:12 PM, Richard Snoke <dsnoke@us.ibm.com> wrote:

> Hi,
>
> All this is just my opinion. You may legitimately disagree or not
believe
> me. Deal with it.
>
> My recollection is that exactly 2 processors, as the term was understood

> prior to multi-core and/or multi-threaded chips, presents an interesting

> problem. If you set MULTIPROCESSOR to zero, then there is no need for
any
> of the multiprocessor serializing or synchronizing code. If you do set
> MULTIPROCESSOR to 1, then all that extra logic is required. In some
> cases, the overhead of that extra work was worse than just letting
things
> run on a single processor. You did not gain nearly enough to justify
> using 2 CPU VPs.
>
> However, and I think its a big however, newer systems will only have
that
> problem if you have a single dual-core, single threaded processor.
> Anything more than that is effectively a symmetric multi-processor
system,
> and MULTIPROCESSOR > 0 shouldn't be a problem. If you want to be really
> picky, and if you have exactly one CPU VP, then perhaps MULTIPROCESSOR
at
> zero makes sense. In that case, be very careful never to add another CPU

> VP or you will probably have problems due to lack of synchronization.
>
> For current systems, I suggest up to (cores*(threads per core))-(some
> integer less than pi) CPU VPs. But I don't agree that one should always
> have as many CPU VPs as the system can manage. Use what your workload
> requires.
>
> Cheers,
> Dick Snoke
> IBM ChannelWorks
>
> dsnoke@us.ibm.com
> (404) 487-1595
>
> From: "kate" <kate@iiug.org>
> To: ids@iiug.org
> Date: 07/22/2010 10:59 AM
> Subject: Multiprocessor setting [20614]
> Sent by: ids-bounces@iiug.org
>
> Hey Gurus,
> A few years back in a performance presentation from John Miller, he
> discussed the correct tuning for 2 CPU systems. He mentioned that the
> MULTIPROCESSOR in the config file should actually be set to 0 (off) for
> two
> CPU systems to stop the engine from doing unnessary spinning waiting for

> the
> next processor. He said that this value only improved the performance of
a
>
> 3 CPU system or more.
>
> My question is - is that still true for version 11.5 and todays new quad

> core CPUs?
>
> Thanks!
> Kate Tomchik [ kate@iiug.org ] www.iiug.org
> International Informix Users Group Board of Directors
>
> A computer lets you make more mistakes faster than any invention in
human
> history - with the possible exceptions of handguns and tequila.
> Mitch Ratliffe
>
>
>
>
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>
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>
>
>
>
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Messages In This Thread

• Multiprocessor setting
  kate -- Thursday, 22 July 2010, at 10:59 a.m.
  • Re: Multiprocessor setting
    Obnoxio The Clown -- Thursday, 22 July 2010, at 11:01 a.m.
    • Re: Multiprocessor setting
      Fernando Nunes -- Thursday, 22 July 2010, at 11:07 a.m.
    • Re: Multiprocessor setting
      Alexandre Marini -- Thursday, 22 July 2010, at 11:15 a.m.
  • RE: Multiprocessor setting
    Wyza, Jonathon -- Thursday, 22 July 2010, at 11:06 a.m.
  • Re: Multiprocessor setting
    Art Kagel -- Thursday, 22 July 2010, at 12:59 p.m.
    • Re: Multiprocessor setting
      Fernando Nunes -- Thursday, 22 July 2010, at 1:03 p.m.
    • RE: Multiprocessor setting
      Paul Watson -- Thursday, 22 July 2010, at 1:06 p.m.
      • RE: Multiprocessor setting
        Wyza, Jonathon -- Thursday, 22 July 2010, at 1:12 p.m.
        • Re: Multiprocessor setting
          Art Kagel -- Thursday, 22 July 2010, at 1:41 p.m.
          • Re: Multiprocessor setting
            Lester Knutsen -- Thursday, 22 July 2010, at 2:11 p.m.
            • Re: Multiprocessor setting
              Art Kagel -- Thursday, 22 July 2010, at 2:35 p.m.
      • Re: Multiprocessor setting
        Art Kagel -- Thursday, 22 July 2010, at 1:46 p.m.
        • Re: Multiprocessor setting
          John Miller iii -- Thursday, 22 July 2010, at 3:00 p.m.
          • RE: Multiprocessor setting
            Wyza, Jonathon -- Thursday, 22 July 2010, at 3:12 p.m.
            • Re: Multiprocessor setting
              Art Kagel -- Thursday, 22 July 2010, at 3:56 p.m.
            • Re: Multiprocessor setting
              Alexandre Marini -- Thursday, 22 July 2010, at 3:57 p.m.
          • Re: Multiprocessor setting
            Fernando Nunes -- Thursday, 22 July 2010, at 6:27 p.m.
  • Re: Multiprocessor setting
    Richard Snoke -- Thursday, 22 July 2010, at 2:12 p.m.
    • Re: Multiprocessor setting
      Art Kagel -- Thursday, 22 July 2010, at 2:46 p.m.
      • Re: Multiprocessor setting
        Richard Snoke -- Thursday, 22 July 2010, at 3:12 p.m.

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