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Re: processor running queue - general rule of thumb?

From: Alan McKay <alan(dot)mckay(at)gmail(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: processor running queue - general rule of thumb?
Date: 2009-06-23 20:41:53
Message-ID: 844129e80906231341x7827501bje97fc2c1b1939135@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
BTW, our designer got the nytprofile or whatever it is called for Perl
and found out that it was a problem with the POE library that was
being used as a state-machine to drive the whole load suite.   It was
taking something like 95% of the CPU time!

On Fri, Jun 19, 2009 at 11:59 AM, Alan McKay<alan(dot)mckay(at)gmail(dot)com> wrote:
> Hey folks,
>
> I'm new to all this stuff, and am sitting here with kSar looking at
> some graphed results of some load tests we did, trying to figure
> things out :-)
>
> We got some unsatisfactory results in stressing our system, and now I
> have to divine where the bottleneck is.
>
> We did 4 tests, upping the load each time.   The 3rd and 4th ones have
> all 8 cores pegged at about 95%.  Yikes!
>
> In the first test the processor running queue spikes at 7 and maybe
> averages 4 or 5
>
> In the last test it spikes at 33 with an average maybe 25.
>
> Looks to me like it could be a CPU bottleneck.  But I'm new at this :-)
>
> Is there a general rule of thumb "if queue is longer than X, it is
> likely a bottleneck?"
>
> In reading an IBM Redbook on Linux performance, I also see this :
> "High numbers of context switches in connection with a large number of
> interrupts can signal driver or application issues."
>
> On my first test where the CPU is not pegged, context switching goes
> from about 3700 to about 4900, maybe averaging 4100
>
> On the pegged test, the values are maybe 10% higher than that, maybe 15%.
>
> It is an IBM 3550 with 8 cores, 2660.134 MHz (from dmesg), 32Gigs RAM
>
> thanks,
> -Alan
>
> --
> “Don't eat anything you've ever seen advertised on TV”
>         - Michael Pollan, author of "In Defense of Food"
>



-- 
“Don't eat anything you've ever seen advertised on TV”
         - Michael Pollan, author of "In Defense of Food"

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