RFR: 8231717: Improve performance of EBCDIC charset decoding for COMPACT_STRINGS

Fri Oct 4 13:05:50 UTC 2019

Hi Roger,
So based on your suggestion i've removed the logic from the constructor 
and it's now pre-determined by the charset generator tooling, just like 
isASCIICompatible is... It works really nicely, so there is now no impact 
on the constructor. I have verified this using the StrCodingBenchmark 
test. I have also integrated the new method into ArrayDecoder as you said, 
which makes it neater.

Please review the new webrev here: 
http://cr.openjdk.java.net/~aleonard/8231717/webrev.01/

Many thanks
Andrew

Andrew Leonard
Java Runtimes Development
IBM Hursley
IBM United Kingdom Ltd
internet email: andrew_m_leonard at uk.ibm.com 

From:   Roger Riggs <Roger.Riggs at oracle.com>
To:     Andrew Leonard <andrew_m_leonard at uk.ibm.com>
Cc:     core-libs-dev at openjdk.java.net
Date:   02/10/2019 19:27
Subject:        Re: RFR: 8231717: Improve performance of EBCDIC charset 
decoding for COMPACT_STRINGS

Hi Andrew,

On 10/2/19 12:54 PM, Andrew Leonard wrote:
Hi Roger, 
Thank you for the feedback. 
So your point about constructor performance is a good one, in my 
performance tests in which I have run both the StrCodingBenchmark.java 
test and also some simple standalone tests, I did not see any noticeable 
degradation for charsets that are not alwaysCompactable(), but I will look 
closer at that one. It has made me think though that I can do the 
isAlwaysCompactable determination at static init time, since the table is 
obviously static...I will investigate that optimization. 

The change is actually not just EBCDIC, as I point out in the bug it's any 
SingleByte charset that is determined as "alwaysCompactable", I specified 
EBCDIC in the bug title as it is actually just about only the EBCDIC 
charsets that fall into this category. I can rename the "title" maybe?

So I think the name should be closer to everything that can be 
decoded/mapped to Latin1 or 8-bit clean.

The "negatives" check for isASCIICompatible is done only on the input 
bytes when the given charset "isASCIICompatible" as you said. This change 
is not related to hasNegatives() so not sure I quite understand the point 
about moving it? hasNegatives() is relavent to the input byte[] being 
decoded as if it contains negatives it will need complete mapping even for 
an isASCIICompatible charset. 
ok
isAlwaysCompactable is about the charset in general, and can (and I think 
should) be computed at static init time, as it's simply determined by the 
fact that the static b2c[] table maps only to values 0->0xff. 

EBCDIC codepages are not ASCIICompatible as they don't map directly, so 
you cannot combine the two, they are independent scenario fastpaths.
rigth, there is a mapping needed.

If I add a default impl for decodeToLatin1() I could add the methods to 
ArrayDecoder, I will look at that. I think I did it that way as I didn't 
want to affect anyone that may have implemented ArrayDecoder separately...
I was also thinking of ISO_8859_1, that doesn't need a mapping, 
and trying to avoid a multiple separate decisions and data paths.
(while keeping the code simple)

Thanks, Roger

Thanks for the review, I will look at the static init of 
alwaysCompactable, and move the methods to ArrayDecoder, and do a closer 
check on constructor performance at the end of that. 
Cheers 
Andrew 

Andrew Leonard
Java Runtimes Development
IBM Hursley
IBM United Kingdom Ltd
internet email: andrew_m_leonard at uk.ibm.com 

From:        Roger Riggs <Roger.Riggs at oracle.com> 
To:        core-libs-dev at openjdk.java.net 
Date:        02/10/2019 14:52 
Subject:        Re: RFR: 8231717: Improve performance of EBCDIC charset 
decoding for COMPACT_STRINGS 
Sent by:        "core-libs-dev" <core-libs-dev-bounces at openjdk.java.net> 

Hi Andrew,

This would seem to have an impact on the performance of every Decoder 
constructor
because it determines dynamically the isAlwaysCompactable attribute.
Are there regressions in the non-EBCDIC cases?

Did your performance tests include the constructor overhead?

The isASCIICompatible case is handled by checking for negatives only 
when needed.

Unless the information is used more than once it looks like you've moved 
the computation
from StringCoding hasNegatives to the Decoder constructor.

Is there a change that would benefit both the isASCIICompatible case and 
EBCDIC?

Is there a reason you didn't add the isAlwaysCompactable method to the 
existing ArrayDecoder interface.
I don't think there there is a need for a new interface.

Thanks, Roger

On 10/2/19 4:10 AM, Andrew Leonard wrote:
> Hi,
> Please can I request a review of this performance enhancement for EBCDIC
> (and any SingleByte, always compactable) charsets? I've explained the
> theory in the bug (https://bugs.openjdk.java.net/browse/JDK-8231717 ), 
but
> essentially it optimizes any SingleByte charset that is always 
compactable
> due to all mappings being to <=0xff and avoids unnecessary char[] to
> internal Latin1 byte[] arraycopy as a result. This leads to up to a 100%
> performance gain for decoding these charsets.
> I have run the complete tier1 and also the complete sun/nio/cs testcases
> successfully.
>
> Webrev: http://cr.openjdk.java.net/~aleonard/8231717/webrev.00/ 
>
> Thoughts and comments welcome please?
> Thanks
> Andrew
>
> Andrew Leonard
> Java Runtimes Development
> IBM Hursley
> IBM United Kingdom Ltd
> internet email: andrew_m_leonard at uk.ibm.com
>
> Unless stated otherwise above:
> IBM United Kingdom Limited - Registered in England and Wales with number
> 741598.
> Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 
3AU
>

Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 
741598. 
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU