(resend) Request for review (S): 7068625 Testing 8 bytes of card table entries at a time speeds up card-scanning

Bengt Rutisson bengt.rutisson at oracle.com
Fri Feb 24 12:53:19 UTC 2012


On 2012-02-24 13:50, Jesper Wilhelmsson wrote:
> I can have a look at it but I don't have the time to do it today. If 
> Monday is OK then I can take it.

Thanks, Jesper!

Will also need a second review from someone with OpenJDK reviewer status.

Bengt

> /Jesper
>
>
>
> 24 feb 2012 kl. 13:14 skrev Bengt Rutisson <bengt.rutisson at oracle.com 
> <mailto:bengt.rutisson at oracle.com>>:
>
>>
>> Hi all,
>>
>> Just pinging this review request. Does anybody have some time to look 
>> at it? It is a fairly small and straight forward change...
>>
>> Thanks,
>> Bengt
>>
>> -------- Original Message --------
>> Subject: 	Request for review (S): 7068625 Testing 8 bytes of card 
>> table entries at a time speeds up card-scanning
>> Date: 	Tue, 21 Feb 2012 12:03:50 +0400
>> From: 	Alexey Ragozin <alexey.ragozin at gmail.com>
>> To: 	hotspot-gc-dev at openjdk.java.net
>> CC: 	Bengt Rutisson <bengt.rutisson at oracle.com>
>>
>>
>>
>> Hi,
>>
>> I would like few volunteers to review changes for 
>> http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7068625
>> WebRev: http://cr.openjdk.java.net/~brutisso/7068625/webrev.00/ 
>> <http://cr.openjdk.java.net/%7Ebrutisso/7068625/webrev.00/>
>>
>> Change summary
>> For large heaps (I was focusing on 8GiB and above) it is common to 
>> have long continuous ranges of clean cards.
>> Patch is introducing a short path for skipping ranges of clean cards 
>> using word aligned memory access instead of byte aligned.
>>
>> Patch affects serial and CMS collectors. For CMS collector stride 
>> size should be increase to see any performance gains (I was using
>> -XX:+UnlockDiagnosticVMOptions
>> -XX:ParGCCardsPerStrideChunk=4096)
>>
>> For testing I was mainly using synthetic benchmark randomly modifying 
>> hash tables in heap, thus uniformly touching cards across heaps.
>> Average duration of young GC pause were used as KPI.
>> More details about testing can be found at
>> http://blog.ragozin.info/2011/07/openjdk-patch-cutting-down-gc-pause.html
>> Though article is referring jdk6, my resent tests with trunk jdk7 
>> show no difference.
>> I was also tested patch with real application (Oracle Coherence 
>> storage node).
>> With 16GiB of heap and CMS/ParNew GC, enabling patch have shortened 
>> GC pauses roughly in 2 times.
>>
>> Source code of benchmark used in test are available at
>> https://gridkit.googlecode.com/svn/branches/aragozin-sandbox/young-gc-bench
>> Main class YoungGCPauseBenchmark
>>
>> Regards,
>> Alexey
>>

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