Fwd: Reference Processing in G1 remark phase vs. throughput collector

[YU ZHANG]

Jason,

Can you try -XX:+ParallelRefProcEnabled? The default is disabled.

Thanks,
Jenny

On 6/20/2014 9:51 AM, Jason Resch wrote:
>
>
>
> -------- Original Message --------
> Subject: 	Reference Processing in G1 remark phase vs. throughput 
> collector
> Date: 	Wed, 18 Jun 2014 14:20:36 -0500
> From: 	Jason Resch <jresch at cleversafe.com>
> To: 	hotspot-gc-dev at openjdk.java.net <hotspot-gc-dev at openjdk.java.net>
>
>
>
> Hello,
>
> We've recently been experimenting with the G1 collector for our 
> application, and we noticed something odd with reference processing 
> times in the G1. It is not clear to us if this is expected or 
> indicative of a bug, but I thought I would mention it to this list to 
> see if there is a reasonable explanation for this result.
>
> We are seeing that during the remark phase when non-strong references 
> are processed, it takes around 20 times longer than the throughput 
> collector spends processing the same number of references.  As an 
> example, here is some output for references processing times we observed:
>
>     2014-05-23T19:58:12.805+0000: 11446.605: [GC remark 11446.618: [GC
>     ref-proc11446.618: [SoftReference, 0 refs, 0.0040400
>     secs]11446.622: [WeakReference, 11131810 refs, 8.7176900
>     secs]11455.340: [FinalReference, 2273593 refs, 2.0022000
>     secs]11457.342: [PhantomReference, 297950 refs, 0.3004680
>     secs]11457.643: [JNI Weak Reference, 0.0000040 secs], 13.7534950
>     secs], 13.8035420 secs]
>
>
> We see the G1 spent 8.7 seconds were spent processing 11 million weak 
> references
>
>     2014-05-30T05:57:24.002+0000: 32724.998: [Full GC32726.138:
>     [SoftReference, 154 refs, 0.0050380 secs]32726.143:
>     [WeakReference, 7713339 refs, 0.3449380 secs]32726.488:
>     [FinalReference, 1966941 refs, 0.1005860 secs]32726.588:
>     [PhantomReference, 650797 refs, 0.0631680 secs]32726.652: [JNI
>     Weak Reference, 0.0000060 secs] [PSYoungGen:
>     1012137K->0K(14784384K)] [ParOldGen:
>     16010001K->5894387K(16384000K)] 17022139K->5894387K(31168384K)
>     [PSPermGen: 39256K->39256K(39552K)], 4.3463290 secs] [Times:
>     user=98.05 sys=0.00, real=4.35 secs]
>
> While the throughput collector spent 0.34 seconds processing 7.7 
> million weak references
>
>
> In summary, the G1 collector processed weak references at a rate of 
> 1.27 million per second, while the throughput collector processed them 
> at 22.36 million references per second. Is there a fundamental design 
> reason that explains why the G1 collector should be so much slower in 
> this regard, or might there be ways to improve upon it?
>
>
> Jason
>
>
>
>
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