Default performance on Sun T5440

[Jon Masamitsu]

Jeff,

The default number of GC threads was changed to be fewer in
jdk6u14 (same change in jdk7). I'm guessing you're using
an older jdk? The number of GC threads depends on the
number of cores on the platform. I think on the T5440 the
number will be about 3/16 * 256 or 48.

Jon

jeff.lloyd at algorithmics.com wrote On 10/02/09 08:23,:

> Hi,
>
> I just ran my application on a new box from Sun and found immediate
> debilitating java performance by default.
>
> System Configuration: Sun Microsystems sun4v T5440
>
> Memory size: 65248 Megabytes
>
> ================================ Virtual CPUs
> ================================
>
> CPU ID Frequency Implementation Status
>
> ------ --------- ---------------------- -------
>
> 0 1164 MHz SUNW,UltraSPARC-T2+ on-line
>
> 1 1164 MHz SUNW,UltraSPARC-T2+ on-line
>
> …
>
> 254 1164 MHz SUNW,UltraSPARC-T2+ on-line
>
> 255 1164 MHz SUNW,UltraSPARC-T2+ on-line
>
> four UltraSPARC T2 Plus processors per system, 256 threads; 1.2 GHz
>
> The default java behaviour is to use all 256 virtual processors for
> garbage collection, and even for small ParNew collections the system
> was being hammered. The cpu load reported by prstat was 150 during
> too-frequent and long-running YG garbage collections. I had to specify
> -XX:ParallelGCThreads=8 to bring the gc under control.
>
> I just wanted to let you know that the default gc behaviour for Sun’s
> JVM on Sun’s hardware produces undesirable results. I don’t think most
> people will know how to diagnose or fix this problem.
>
> Jeff
>
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