Strange speed dependency

[Ulf Zibis]

Martin,

the reason for my post was to give the HotSpot guys some hint for 
additional enhancement.

BTW, I have used the recent UTF_8 decoder for my reference.
... But I have experienced some errors:
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6795537
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6798514

Most of them I have repaired yet, and fortunately I could enhance the 
speed by another ~20 % (on my machine, should be evaluated).

-Ulf


Am 03.02.2009 00:02, Martin Buchholz schrieb:
> Ulf, the new UTF_8 decoder in very recent jdks is much faster,
> and the primary trick that was used to achieve that
> was reducing the size of the bytecode in the hot methods
> and moving cold code to separate methods.
>
> Martin
>
> On Mon, Feb 2, 2009 at 14:35, Ulf Zibis <Ulf.Zibis at gmx.de> wrote:
>   
>> Hi all,
>>
>> I have experienced a strange speed dependency of HotSpot compiled code after
>> little change in code, which is not part of the "hot" loop.
>> Is there any explanation for this behavior?
>>
>> Code before little change:
>>
>> class UTF_8_new extends Unicode {
>>
>>       // ....
>>
>>       private static CoderResult malformed(ByteBuffer src, int sp,
>>                                            CharBuffer dst, int dp, int nb) {
>>           src.position(sp -= nb - src.arrayOffset());
>>           CoderResult cr = malformedN(src, nb);
>>           updatePositions(src, sp, dst, dp);
>>           return cr;
>>       }
>>
>>       // ....
>>
>>           while (sp < sl) {
>>               // ....
>>                   int b2 = sa[sp++];
>>                   int b3 = sa[sp++];
>>                   int b4 = sa[sp++];
>>                   if (isMalformed4(b1, b2))
>>                       return malformed(src, sp-2, dst, dp, 2);
>>                   if (isNotContinuation(b3))
>>                       return malformed(src, sp-1, dst, dp, 3);
>>                   if (isNotContinuation(b4))
>>                       return malformed(src, sp, dst, dp, 4);
>>                   if (dp >= dl - 1)
>>                       return overflow(src, sp-4, dst, dp);
>>                   int uc = (b1 << 18) ^ (b2 << 12) ^ (b3 << 06) ^ b4 ^
>> 0x00381f80;
>>               // ....
>>           }
>>
>> The above code has following output (note gain against UTF_8_70$Decoder):
>> time for sun.nio.cs.UTF_8_60$Decoder: 2701 ms
>> time for sun.nio.cs.UTF_8_70$Decoder: 1984 ms
>> time for sun.nio.cs.UTF_8_new$Decoder: 1720 ms  // gain: 264 ms
>> time for sun.nio.cs.UTF_8_last$Decoder: 2110 ms
>>
>>
>> Following small code change made the "hot" part of the loop much slower:
>>
>> class UTF_8_new extends Unicode {
>>
>>       // ....
>>
>>       private static CoderResult malformed(ByteBuffer src, int sp,
>>                                            CharBuffer dst, int dp, int nb) {
>>           src.position(sp - src.arrayOffset());    // removed subtraction of
>> nb
>>           CoderResult cr = malformedN(src, nb);
>>           updatePositions(src, sp, dst, dp);
>>           return cr;
>>       }
>>
>>       // ....
>>
>>           while (sp < sl) {
>>               // ....
>>                   int b2 = sa[sp++];
>>                   int b3 = sa[sp++];
>>                   int b4 = sa[sp++];
>>                   if (isMalformed4(b1, b2))
>>                       return malformed(src, sp-4, dst, dp, 2);
>>                   if (isNotContinuation(b3))
>>                       return malformed(src, sp-4, dst, dp, 3);
>>                   if (isNotContinuation(b4))
>>                       return malformed(src, sp-4, dst, dp, 4);
>>                   if (dp >= dl - 1)
>>                       return overflow(src, sp-4, dst, dp);
>>                   int uc = (b1 << 18) ^ (b2 << 12) ^ (b3 << 06) ^ b4 ^
>> 0x00381f80;
>>               // ....
>>           }
>>
>> time for sun.nio.cs.UTF_8_60$Decoder: 2731 ms
>> time for sun.nio.cs.UTF_8_70$Decoder: 1981 ms
>> time for sun.nio.cs.UTF_8_new$Decoder: 1872 ms  // gain: 109 ms
>> time for sun.nio.cs.UTF_8_last$Decoder: 2094 ms
>>
>> For complete sources compare following revisions (... and run
>> UTF_8Benchmark.java ):
>> https://java-nio-charset-enhanced.dev.java.net/source/browse/java-nio-charset-enhanced/trunk/test/sun/nio/cs/?diff_format=s&rev=613
>> https://java-nio-charset-enhanced.dev.java.net/source/browse/java-nio-charset-enhanced/trunk/test/sun/nio/cs/?diff_format=s&rev=614
>>
>>
>> -Ulf
>>
>>
>>
>>
>>     
>
>
>