RFR(XS): 8151030: PPC64: AllocatePrefetchStyle=4 is out of range

[Michihiro Horie]

Hi Martin, Lutz,

I have not seen big differences in SPECjbb2015 scores both on P8 and P9.

Best regards,
Michihiro


 ----- Original message -----
 From: "Schmidt, Lutz" <lutz.schmidt at sap.com>
 To: Michihiro Horie <HORIE at jp.ibm.com>, "Doerr, Martin"
 <martin.doerr at sap.com>
 Cc: "ppc-aix-port-dev at openjdk.java.net"
 <ppc-aix-port-dev at openjdk.java.net>,
 "hotspot-compiler-dev at openjdk.java.net"
 <hotspot-compiler-dev at openjdk.java.net>
 Subject: [EXTERNAL] Re: RFR(XS): 8151030: PPC64: AllocatePrefetchStyle=4
 is out of range
 Date: Thu, Apr 23, 2020 3:01 AM

 Hi Martin,

 your change looks good to me.

 I noticed you didn't find a chance to put it in the patch queue for our
 internal testing. I did that now, but it's too late for tonight. We'll
 have to wait until Friday morning (GMT+2) to really see what I expect: no
 issues.

 Thanks for cleaning up this old stuff.

 Regards,
 Lutz


 On 21.04.20, 16:57, "hotspot-compiler-dev on behalf of Michihiro Horie"
 <hotspot-compiler-dev-bounces at openjdk.java.net on behalf of
 HORIE at jp.ibm.com> wrote:


     Hi Martin,

     I started measuring SPECjbb2015 to see the performance impact on P9.
 Also,
     I'm preparing same measurement on P8.

     Best regards,
     Michihiro


      ----- Original message -----
      From: "Doerr, Martin" <martin.doerr at sap.com>
      To: "'hotspot-compiler-dev at openjdk.java.net'"
      <hotspot-compiler-dev at openjdk.java.net>
      Cc: Michihiro Horie <HORIE at jp.ibm.com>, "cjashfor at linux.ibm.com"
      <cjashfor at linux.ibm.com>, "ppc-aix-port-dev at openjdk.java.net"
      <ppc-aix-port-dev at openjdk.java.net>, Gustavo Romero
      <gromero at linux.vnet.ibm.com>, "joserz at linux.ibm.com"
      <joserz at linux.ibm.com>
      Subject: [EXTERNAL] RFR(XS): 8151030: PPC64: AllocatePrefetchStyle=4
 is
      out of range
      Date: Tue, Apr 14, 2020 11:07 PM

      Hi,

      I’d like to resolve a very old PPC64 issue:

 https://urldefense.proofpoint.com/v2/url?u=https-3A__bugs.openjdk.java.net_browse_JDK-2D8151030&d=DwIGaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=oecsIpYF-cifqq2i1JEH0Q&m=Q3El2qgCsQyK-bunbC8-3yZzMvfZGBwC8q58omWEUCM&s=ohXZhHZXhsm01dbRh1iQHwrtNAH1QfUmokv2qs49cPY&e=


      There’s code for AllocatePrefetchStyle=4 which is not an accepted
 option.
      It was used for a special experimental prefetch mode using dcbz
      instructions to combine prefetching and zeroing in the TLABs.
      However, this code was never contributed and there are no plans to
 work on
      it. So I’d like to simply remove this small part of it.

      In addition to that, AllocatePrefetchLines is currently set to 3 by
      default which doesn’t make sense to me. PPC64 has an automatic
 prefetch
      engine and executing several prefetch instructions for succeeding
 cache
      lines doesn’t seem to be beneficial at all.
      So I’m setting it to 1 by default. I couldn’t observe regressions on
      Power7, Power8 and Power9.

      Webrev:

 https://urldefense.proofpoint.com/v2/url?u=http-3A__cr.openjdk.java.net_-7Emdoerr_8151030-5Fppc-5Fprefetch_webrev.00_&d=DwIGaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=oecsIpYF-cifqq2i1JEH0Q&m=Q3El2qgCsQyK-bunbC8-3yZzMvfZGBwC8q58omWEUCM&s=paesC67BcmFOkkYjGySj1AUJJyOKHO25BwzZi0vHG8g&e=


      Please review.

      If somebody from IBM would like to check performance impact of
 changing
      the AllocatePrefetchLines + Distance, I’ll be glad to receive
 feedback.

      Best regards,
      Martin