RFR: 8220566: AArch64: Set default vm features for Ampere eMAG CPUs

Patrick Zhang OS patrick at os.amperecomputing.com
Thu Mar 14 09:10:44 UTC 2019

Hi Andrew,
Sure, please, thank you very much for sponsoring this.


-----Original Message-----
From: Andrew Dinn <adinn at redhat.com> 
Sent: Thursday, March 14, 2019 5:03 PM
To: Patrick Zhang OS <patrick at os.amperecomputing.com>
Cc: aarch64-port-dev at openjdk.java.net; hotspot-runtime-dev at openjdk.java.net
Subject: Re: RFR: 8220566: AArch64: Set default vm features for Ampere eMAG CPUs

Hi Patrick,

On 14/03/2019 04:05, Patrick Zhang OS wrote:
> I added below comments in JIRA, also copied here. Thanks for your 
> review.
> https://bugs.openjdk.java.net/browse/JDK-8220566?focusedCommentId=1425
> 1292&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabp
> anel#comment-14251292  These three flags had been verified on Ampere 
> eMAG platform with a couple of benchmarks and apps 
> AvoidUnalignedAccesses=TRUE, UseSIMDForMemoryOps=TRUE can bring 
> positive impact consistently, since access to odd alignment memory is 
> not what we expect, and simd instructions replacement for mem/array 
> copying practically helps performance. While for 
> UseSIMDForArrayEquals=TRUE (default), I am not quite sure yet what 
> took more execution time, either ld1 or umov, or the sequence 
> generated inside generate_large_array_equals_loop_simd.
> Therefore I make it FALSE within a stricter condition for CPU 
> revisions I have so far.

Thank you for making your decisions clear. I am happy to accept your choice of defaults so this patch can be pushed. Do you need me to do that for you?


Andrew Dinn
Senior Principal Software Engineer
Red Hat UK Ltd
Registered in England and Wales under Company Registration No. 03798903
Directors: Michael Cunningham, Michael ("Mike") O'Neill, Eric Shander

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