RFR JDK-6321472: Add CRC-32C API
Staffan Friberg
staffan.friberg at oracle.com
Wed Oct 22 17:54:56 UTC 2014
You're right, managed to convince myself here as well. Will change it to <=.
An unfortunate side-effect seems to be that in a benchmark with 1024
long array it seems like the performance drops when the tail loop is not
utilized.
As you can see below there is a slight drop when the data is perfectly
aligned in the array causing neither alignment or tail loop to be utilized.
Not going to dig into why right now, but an interesting effect.
@Benchmark
@OperationsPerInvocation(1024)
public void byteArray_1K() {
checksum.update(unalignedByteArray_1k, offset, 1024);
}
Benchmark (offset) Mode Samples Score Score error Units
o.c.CRC32CUnaligned.byteArray_1K 0 thrpt 5 983198.048 654.467 ops/ms
o.c.CRC32CUnaligned.byteArray_1K 1 thrpt 5 1013136.714 3801.537 ops/ms
o.c.CRC32CUnaligned.byteArray_1K 2 thrpt 5 1006899.265 10998.612 ops/ms
o.c.CRC32CUnaligned.byteArray_1K 3 thrpt 5 1014419.366 3745.875 ops/ms
o.c.CRC32CUnaligned.byteArray_1K 4 thrpt 5 1007777.937 1585.989 ops/ms
o.c.CRC32CUnaligned.byteArray_1K 5 thrpt 5 1011249.564 852.333 ops/ms
o.c.CRC32CUnaligned.byteArray_1K 6 thrpt 5 1013622.327 4075.303 ops/ms
o.c.CRC32CUnaligned.byteArray_1K 7 thrpt 5 1008137.616 1672.262 ops/ms
o.c.CRC32CUnaligned.byteArray_1K 8 thrpt 5 985838.295 448.735 ops/ms
o.c.CRC32CUnaligned.byteArray_1K 9 thrpt 5 1005935.356 4250.381 ops/ms
o.c.CRC32CUnaligned.byteArray_1K 10 thrpt 5 995912.149 2447.272 ops/ms
With just using < then the performance is equal across all alignments.
Benchmark (offset) Mode Samples Score Score error Units
o.c.CRC32CUnaligned.byteArray_1K 0 thrpt 5 1003094.419 2656.518 ops/ms
o.c.CRC32CUnaligned.byteArray_1K 1 thrpt 5 1009641.996 2519.614 ops/ms
o.c.CRC32CUnaligned.byteArray_1K 2 thrpt 5 1009169.464 12987.786 ops/ms
o.c.CRC32CUnaligned.byteArray_1K 3 thrpt 5 1006869.144 1617.988 ops/ms
o.c.CRC32CUnaligned.byteArray_1K 4 thrpt 5 1005490.644 1234.283 ops/ms
o.c.CRC32CUnaligned.byteArray_1K 5 thrpt 5 1007468.090 327.541 ops/ms
o.c.CRC32CUnaligned.byteArray_1K 6 thrpt 5 1014316.244 1174.920 ops/ms
o.c.CRC32CUnaligned.byteArray_1K 7 thrpt 5 1008378.002 1440.734 ops/ms
o.c.CRC32CUnaligned.byteArray_1K 8 thrpt 5 1003253.408 10786.210 ops/ms
o.c.CRC32CUnaligned.byteArray_1K 9 thrpt 5 1000950.362 250.617 ops/ms
o.c.CRC32CUnaligned.byteArray_1K 10 thrpt 5 1003783.897 11333.132 ops/ms
//Staffan
On 10/21/2014 10:56 PM, Peter Levart wrote:
> On 10/21/2014 11:34 PM, Staffan Friberg wrote:
>> I believe it must be <, as it is in the tail loop as well, because
>> end is (off+len or limit) so end is exclusive, similar to
>> subString(begin,end).
>>
>> Makes sense?
>>
>> //Staffan
>>
>> On 10/21/2014 01:46 PM, Peter Levart wrote:
>>> Sorry Staffan, another nit...
>>>
>>> 212 for (; off < (end - Long.BYTES); off += Long.BYTES) {
>>> and
>>>
>>> 286 for (; off < (end - Long.BYTES); off += Long.BYTES) {
>>>
>>>
>>> I think you could change "off < (end - Long.BYTES)" to "off <= (end
>>> - Long.BYTES)". Am I right?
>
> The tail loop has < :
>
> 319 for (; off < end; off++) {
>
>
> ...but it could be written as:
>
>
> for (; off <= (end - Byte.BYTES); off += Byte.BYTES) { ...
>
>
> ;-)
>
> In other words, when off == end - Long.BYTES, you can still read
> Long.BYTES starting at 'off' .
>
> Regards, Peter
>
>
>>>
>>> Regards, Peter
>>>
>>>
>>> On 10/21/2014 10:30 PM, Peter Levart wrote:
>>>>
>>>> On 10/21/2014 08:49 PM, Staffan Friberg wrote:
>>>>> Hi,
>>>>>
>>>>> Got an offline comment that the package.html should be update as
>>>>> well to cover CRC-32C.
>>>>>
>>>>> Otherwise there are no code changes in this new webrev.
>>>>>
>>>>> http://cr.openjdk.java.net/~sfriberg/JDK-6321472/webrev.04
>>>>
>>>>
>>>> Hi Staffan,
>>>>
>>>> 198 if (end - off >= 8 &&
>>>> Unsafe.ARRAY_BOOLEAN_INDEX_SCALE == 1) {
>>>>
>>>> ARRAY_BOOLEAN_INDEX_SCALE -> ARRAY_BYTE_INDEX_SCALE
>>>>
>>>>
>>>> Otherwise looks good now.
>>>>
>>>> Regards, Peter
>>>>
>>>> P.S.
>>>>
>>>> I think (by looking at DirectByteBuffer.asIntBuffer()
>>>> implementation) that when doing 32 bit (4 byte) reads using Unsafe,
>>>> the address only has to be aligned to 4 bytes (8 is necessary
>>>> alignment for 64 bit reads). So updateDirectByteBuffer could make
>>>> this alignment on 4 bytes as it's only using 32 bit reads (with
>>>> additional check on ADDRESS_SIZE, you could do that for updateBytes
>>>> too).
>>>>
>>>> You don't get much out of it, so you decide if it's worth
>>>> complication.
>>>>
>>>>
>>>>>
>>>>> //Staffan
>>>>>
>>>>> On 10/21/2014 10:28 AM, Staffan Friberg wrote:
>>>>>> Hi Peter,
>>>>>>
>>>>>> Thanks for the comments..
>>>>>>>
>>>>>>> 217 if (Unsafe.ADDRESS_SIZE == 4) {
>>>>>>> 218 // On 32 bit platforms read two ints
>>>>>>> instead of a single 64bit long
>>>>>>>
>>>>>>> When you're reading from byte[] using Unsafe (updateBytes), you
>>>>>>> have the option of reading 64bit values on 64bit platforms. When
>>>>>>> you're reading from DirectByteBuffer memory
>>>>>>> (updateDirectByteBuffer), you're only using 32bit reads.
>>>>>> I will add a comment in the code for this decision. The reason is
>>>>>> that read a long results in slightly worse performance in this
>>>>>> case, in updateBytes it is faster. I was able to get it to run
>>>>>> slightly faster by working directly with the address instead of
>>>>>> always adding address + off, but this makes things worse in the
>>>>>> 32bit case since all calculation will now be using long
>>>>>> variables. So using the getInt as in the current code feels like
>>>>>> the best solution as it strikes the best balance between 32 and
>>>>>> 64bit. Below is how updateByteBuffer looked with the rewrite I
>>>>>> mentioned.
>>>>>>
>>>>>>
>>>>>> ong address = ((DirectBuffer) buffer).address();
>>>>>> crc = updateDirectByteBuffer(crc, address + pos, address + limit);
>>>>>>
>>>>>>
>>>>>> private static int updateDirectByteBuffer(int crc, long adr,
>>>>>> long end) {
>>>>>>
>>>>>> // Do only byte reads for arrays so short they can't be
>>>>>> aligned
>>>>>> if (end - adr >= 8) {
>>>>>>
>>>>>> // align on 8 bytes
>>>>>> int alignLength = (8 - (int) (adr & 0x7)) & 0x7;
>>>>>> for (long alignEnd = adr + alignLength; adr <
>>>>>> alignEnd; adr++) {
>>>>>> crc = (crc >>> 8)
>>>>>> ^ byteTable[(crc ^ UNSAFE.getByte(adr)) &
>>>>>> 0xFF];
>>>>>> }
>>>>>>
>>>>>> if (ByteOrder.nativeOrder() == ByteOrder.BIG_ENDIAN) {
>>>>>> crc = Integer.reverseBytes(crc);
>>>>>> }
>>>>>>
>>>>>> // slicing-by-8
>>>>>> for (; adr < (end - Long.BYTES); adr += Long.BYTES) {
>>>>>> int firstHalf;
>>>>>> int secondHalf;
>>>>>> if (Unsafe.ADDRESS_SIZE == 4) {
>>>>>> // On 32 bit platforms read two ints instead
>>>>>> of a single 64bit long
>>>>>> firstHalf = UNSAFE.getInt(adr);
>>>>>> secondHalf = UNSAFE.getInt(adr + Integer.BYTES);
>>>>>> } else {
>>>>>> long value = UNSAFE.getLong(adr);
>>>>>> if (ByteOrder.nativeOrder() ==
>>>>>> ByteOrder.LITTLE_ENDIAN) {
>>>>>> firstHalf = (int) value;
>>>>>> secondHalf = (int) (value >>> 32);
>>>>>> } else { // ByteOrder.BIG_ENDIAN
>>>>>> firstHalf = (int) (value >>> 32);
>>>>>> secondHalf = (int) value;
>>>>>> }
>>>>>> }
>>>>>> crc ^= firstHalf;
>>>>>> if (ByteOrder.nativeOrder() ==
>>>>>> ByteOrder.LITTLE_ENDIAN) {
>>>>>> crc = byteTable7[crc & 0xFF]
>>>>>> ^ byteTable6[(crc >>> 8) & 0xFF]
>>>>>> ^ byteTable5[(crc >>> 16) & 0xFF]
>>>>>> ^ byteTable4[crc >>> 24]
>>>>>> ^ byteTable3[secondHalf & 0xFF]
>>>>>> ^ byteTable2[(secondHalf >>> 8) & 0xFF]
>>>>>> ^ byteTable1[(secondHalf >>> 16) & 0xFF]
>>>>>> ^ byteTable0[secondHalf >>> 24];
>>>>>> } else { // ByteOrder.BIG_ENDIAN
>>>>>> crc = byteTable0[secondHalf & 0xFF]
>>>>>> ^ byteTable1[(secondHalf >>> 8) & 0xFF]
>>>>>> ^ byteTable2[(secondHalf >>> 16) & 0xFF]
>>>>>> ^ byteTable3[secondHalf >>> 24]
>>>>>> ^ byteTable4[crc & 0xFF]
>>>>>> ^ byteTable5[(crc >>> 8) & 0xFF]
>>>>>> ^ byteTable6[(crc >>> 16) & 0xFF]
>>>>>> ^ byteTable7[crc >>> 24];
>>>>>> }
>>>>>> }
>>>>>>
>>>>>> if (ByteOrder.nativeOrder() == ByteOrder.BIG_ENDIAN) {
>>>>>> crc = Integer.reverseBytes(crc);
>>>>>> }
>>>>>> }
>>>>>>
>>>>>> // Tail
>>>>>> for (; adr < end; adr++) {
>>>>>> crc = (crc >>> 8)
>>>>>> ^ byteTable[(crc ^ UNSAFE.getByte(adr)) & 0xFF];
>>>>>> }
>>>>>>
>>>>>> return crc;
>>>>>> }
>>>>>>
>>>>>>
>>>>>>>
>>>>>>> Also, in updateBytes, the usage of
>>>>>>> Unsafe.ARRAY_INT_INDEX_SCALE/ARRAY_LONG_INDEX_SCALE to index a
>>>>>>> byte array sounds a little scary. To be ultra portable you could
>>>>>>> check that ARRAY_BYTE_INDEX_SCALE == 1 first and refuse to use
>>>>>>> Unsafe for byte arrays if it is not 1. Then use
>>>>>>> Integer.BYTES/Long.BYTES to manipulate 'offsets' instead. In
>>>>>>> updateDirectByteBuffer it would be more appropriate to use
>>>>>>> Integer.BYTES/Long.BYTES too.
>>>>>> Good idea. Added a check in the initial if statement and it will
>>>>>> get automatically optimized away.
>>>>>>
>>>>>>> 225 firstHalf = (int) (value & 0xFFFFFFFF);
>>>>>>> 226 secondHalf = (int) (value >>> 32);
>>>>>>> 227 } else { // ByteOrder.BIG_ENDIAN
>>>>>>> 228 firstHalf = (int) (value >>> 32);
>>>>>>> 229 secondHalf = (int) (value &
>>>>>>> 0xFFFFFFFF);
>>>>>>>
>>>>>>> firstHalf = (int) value; // this is equivalent for line 225
>>>>>>> secondHalf = (int) value; // this is equivalent for line 229
>>>>>> Done.
>>>>>>
>>>>>> Here is the latest webrev,
>>>>>> http://cr.openjdk.java.net/~sfriberg/JDK-6321472/webrev.03
>>>>>>
>>>>>> Cheers,
>>>>>> Staffan
>>>>>
>>>>
>>>
>>
>>
>
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