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https://issues.apache.org/jira/browse/DIRMINA-751?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12787147#action_12787147
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Emmanuel Lecharny commented on DIRMINA-751:
-------------------------------------------
Interesting work :)
I must admit that when I saw your very first patch ( the missing <<20), and had
a look at this atrocious switch I though "man, there should be a way to get
this code better and faster" !. But I was short on time, so I just applied the
patch ...
Now, looking at your second patch, I'm wondering if something like :
protected static int normalizeCapacity( int requestedCapacity ) {
if (requestedCapacity < 0) {
return Integer.MAX_VALUE;
}
int newCapacity = Integer.highestOneBit(requestedCapacity);
newCapacity <<= (newCapacity < requestedCapacity ? 1 : 0);
return (newCapacity < 0 ? Integer.MAX_VALUE : newCapacity);
}
would not do the trick in for lines ?
Ar you interested in testing it, and check the kind of performance you get out
of it ? On mu Mac book pro, your test using the old method took 4444ms/5031ms,
the new one takes 696ms/668ms, which represent 6 to 7 times improvments...
Thanks a lot for investigating the code !
Btw, there is some missing part of code in your patch, the
> IoBuffer.normalizeCapacity improvement
> --------------------------------------
>
> Key: DIRMINA-751
> URL: https://issues.apache.org/jira/browse/DIRMINA-751
> Project: MINA
> Issue Type: Improvement
> Components: Core
> Affects Versions: 2.0.0-RC1
> Environment: N/A
> Reporter: Bogdan Pistol
> Priority: Minor
> Fix For: 2.0.0-RC1
>
> Attachments: IoBufferTest.java, patch.txt
>
>
> The technique of computing the minimum power of 2 that is bigger than the
> requestedCapacity in the
> org.apache.mina.core.buffer.IoBuffer.normalizeCapacity() is not optimal.
> The current computation is as follows:
> int newCapacity = 1;
> while ( newCapacity < requestedCapacity ) {
> newCapacity <<= 1;
> if ( newCapacity < 0 ) {
> return Integer.MAX_VALUE;
> }
> }
> The time complexity of this is O(n), where n is the number of bits of the
> requestedCapacity integer, that is log2(requestedCapacity) - maximum 31.
> This creates an unnecessary overhead in some high IoBuffer allocations
> scenarios that are calling IoBuffer.normalizeCapacity() a lot when creating
> IoBuffers. I observed this when benchmarking a MINA server with hprof.
> There is a better solution to this problem than to iterate the bits from 0 to
> log2(requestedCapacity).
> The alternative is to use a binary search technique that has optimal time
> complexity of O(5). Because requestedCapacity is an integer and has a maximum
> of 2^5 (32) bits we can binary search in the set of bits and determine in
> O(5) comparisons the minimum power of 2 that is bigger than the
> requestedCapacity.
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