RFR: 8179527: Ineffective use of volatile hurts performance of Charset.atBugLevel()

[Kazunori Ogata]

Hi Sean,

Thank you for your suggestion.

Langer, Christoph has gave me the same comment and redirected the RFR to 
core-libs-dev and nio-dev.  Sorry for not telling it here jdk10-dev 
earlier.


Regards,
Ogata


Seán Coffey <sean.coffey at oracle.com> wrote on 2017/06/27 17:40:06:

> From: Seán Coffey <sean.coffey at oracle.com>
> To: Kazunori Ogata <OGATAK at jp.ibm.com>, 
ppc-aix-port-dev at openjdk.java.net,
> nio-dev at openjdk.java.net
> Cc: jdk10-dev at openjdk.java.net
> Date: 2017/06/27 17:40
> Subject: Re: RFR: 8179527: Ineffective use of volatile hurts performance 

> of Charset.atBugLevel()
> 
> This should be reviewed on nio-dev. Please drop jdk10-dev on reply.
> 
> The atBugLevel(String) method seems to be more for legacy use from JDK 
> 1.4/1.5 family. Maybe it's time to drop its use?  We'd need to check if 
> the VM.isBooted() call is still necessary.
> 
> regards,
> Sean.
> 
> On 27/06/2017 06:12, Kazunori Ogata wrote:
> > Hi all, please review a change for JDK-8182743.
> >
> > Bug report: https://bugs.openjdk.java.net/browse/JDK-8182743
> > Webrev: http://cr.openjdk.java.net/~horii/8179527/webrev.00/
> >
> > This change removes a "volatile" qualifier of a static variable used 
by
> > Charset.atBugLevel() because it does not improve thread-safety of the 
code
> > and it hurts performance on PPC (and should be the same in ARM, too).
> > Removing the "volatile" improved performance by 26% in a POWER8 
machine
> > using following micro benchmark:
> >
> > ------
> > import java.io.*;
> > import java.nio.ByteBuffer;
> > import java.nio.charset.Charset;
> > import java.util.ArrayList;
> >
> > class ConvertTest {
> >      static String str;
> >
> >      public static void main(String[] args) {
> >          byte buf[] = { 0x41 };
> >          Charset fromCharset = Charset.forName("iso-8859-1");
> >
> >          long start = System.currentTimeMillis();
> >
> >          for(long i = 0; i < 100000000; i++)
> >              str = new String(buf, 0, 1, fromCharset);
> >
> >          long end = System.currentTimeMillis();
> >
> >          System.out.println("Elapsed: "+(end-start)+" ms");
> >      }
> > }
> > ------
> >
> >
> > Regards,
> > Ogata
> >
>