RFR: 8231717: Improve performance of EBCDIC charset decoding for COMPACT_STRINGS
Andrew Leonard
andrew_m_leonard at uk.ibm.com
Wed Oct 2 16:54:58 UTC 2019
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?
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. 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.
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...
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://urldefense.proofpoint.com/v2/url?u=https-3A__bugs.openjdk.java.net_browse_JDK-2D8231717&d=DwICaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=NaV8Iy8Ld-vjpXZFDdTbgGlRTghGHnwM75wUPd5_NUQ&m=-rKUlQuiG0c80g_6taHF1xicVgTGLhZC0DQZzIrZC54&s=rZFusfU4b1q1rCMGEv_Ex05kXpMHHWdHsZdEbue6Oz0&e=
), 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:
https://urldefense.proofpoint.com/v2/url?u=http-3A__cr.openjdk.java.net_-7Ealeonard_8231717_webrev.00_&d=DwICaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=NaV8Iy8Ld-vjpXZFDdTbgGlRTghGHnwM75wUPd5_NUQ&m=-rKUlQuiG0c80g_6taHF1xicVgTGLhZC0DQZzIrZC54&s=LvQIS6ORN5ZsNhwROkLLLEy_LXKv_v3FLrSCuxhPeDc&e=
>
> 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
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