IDS Forum

Re: cpuvp efficiency AIX 7.1/IDS 11.5.FC8

Posted By: Paul Watson
Date: Friday, 26 June 2015, at 10:50 a.m.

In Response To: Re: cpuvp efficiency AIX 7.1/IDS 11.5.FC8 (Art Kagel)

I would also add, test with SMT off - I have found you can drive the
server harder sooner with SMT disabled, although the absolute max
throughput was the same. Your sysadmins will hate turning off SMT, but it
is an easy test to do

Cheers
Paul

> Mark:
>
> As I understand it, the efficiency is a ratio of time spent by the CPU VPs
> in processing server threads against total CPU time which would include
> polling, spinning, etc. In theory the higher the efficiency the fewer
> cycles are being wasted. Some use it to determine whether there are too
> many CPU VPs (if efficiency is low). I do not follow that myself.
> Assuming that there are more concurrent client sessions I want sufficient
> CPU VPs to process all active user threads (so sqlexec, sort threads, scan
> threads, merge threads, etc.) in parallel. Or, at least, as many as the
> CPU cores can handle.
>
> When I overclock the CPU VPs (which is what I call it when there are more
> CPU VPs than processor cores) the efficiency of the CPU VPs goes down so
> those who follow the efficiency would deduce that there are more VPs than
> are needed. However, I know that overclocked the server is more responsive
> and gets more work done.
>
> A perfect example is a client I recently worked with. They were running a
> P7 system with 5 processor cores (so 20 hardware SMP threads) and 5 CPU
> VPs
> and processing 20 complex transactions a second. I overclocked them to 20
> CPU VPs and increased throughput to 120 transactions per second pushing
> the
> cores to 99% utilization. So a 300% increase in CPU VPs resulted in a 500%
> increase in throughput. We needed more cores to reach their SLA
> requirements so we tested the theory that adding CPU cores would scale
> linearly. First we added one core without adding any CPU VPs. Throughput
> increase by a small amount but not significantly and idle time was around
> 8-12% across all 6 cores. Then I added four more CPU VPs an 18% increase
> in the number of VPs. Processor idle time went down to 1-3% and
> transaction throughput improved by ... 18%,
>
> Efficiency with one VP per core was around 75% with 40% idle time on the
> processors. With four VPs per core it was around 25% with 1-3% idle time.
> Far worse "efficiency" numbers but far better performance!
>
> Do I recommend running the machine at close to 100% under normal
> conditions? No, they need headroom for growth, but that just means they
> need more cores to meet their SLAs and also have some headroom on the box
> for the future.
>
> Art
>
> Art S. Kagel, President and Principal Consultant
> ASK Database Management
> www.askdbmgt.com
>
> Blog: http://informix-myview.blogspot.com/
>
> Disclaimer: Please keep in mind that my own opinions are my own opinions
> and do not reflect on 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 Fri, Jun 26, 2015 at 9:31 AM, MARK SCRANTON <mark@markscranton.com>
> wrote:
>
>> AIX 7.1
>> lpar info:mode=Uncapped smt=On lcpu=16 mem=32768MB psize=6 ent=2.00
>> 16 CPUVPS; IDS 11.5.FC8
>>
>> Question regarding cpu efficiency (a metric I've never played much
>> with).
>> An
>> "onstat -g glo" shows cpuvp efficiency ranges from 12-14% all the time.
>> Similar in production (bigger box, higher entitlement, etc.) I'm not
>> worried
>> about "load balancing" - in earlier IDS we didn't try to load
>> balance/time
>> slice, etc. and haven't heard that that has changed. Anyone have
>> concerns
>> about efficiency being in the this range all the time?
>>
>> Thanks -
>> Mark Scranton
>> The Mark Scranton Group
>> mark@markscranton.com
>>
>>
>>
>>
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--
Paul Watson
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Messages In This Thread

• cpuvp efficiency AIX 7.1/IDS 11.5.FC8
  MARK SCRANTON -- Friday, 26 June 2015, at 9:31 a.m.
  • RE: cpuvp efficiency AIX 7.1/IDS 11.5.FC8
    Alexandre Marini -- Friday, 26 June 2015, at 9:59 a.m.
  • Re: cpuvp efficiency AIX 7.1/IDS 11.5.FC8
    Art Kagel -- Friday, 26 June 2015, at 10:44 a.m.
    • Re: cpuvp efficiency AIX 7.1/IDS 11.5.FC8
      Paul Watson -- Friday, 26 June 2015, at 10:50 a.m.
      • Re: cpuvp efficiency AIX 7.1/IDS 11.5.FC8
        Art Kagel -- Friday, 26 June 2015, at 10:54 a.m.
  • RE: cpuvp efficiency AIX 7.1/IDS 11.5.FC8
    Andrew Ford -- Friday, 26 June 2015, at 11:03 a.m.

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