[11u] RFR 8245512: CRC32 optimization using AVX512 instructions

[Viswanathan, Sandhya]

Hi Andrew,

I understand the dilemma. 
We see ~2x performance gain which is significant, and the patch is very self-contained with no impact on other architectures. 
CRC calculation is prevalent in big Java frameworks, so the request here.
I hope exception can be made for this request. 

This is my first performance backport request for JDK 11. We do understand the balance that you need to maintain in accepting such requests.

Best Regards,
Sandhya

-----Original Message-----
From: Andrew Haley <aph at redhat.com> 
Sent: Wednesday, January 06, 2021 1:57 AM
To: Langer, Christoph <christoph.langer at sap.com>; Viswanathan, Sandhya <sandhya.viswanathan at intel.com>; Doerr, Martin <martin.doerr at sap.com>; Lindenmaier, Goetz <goetz.lindenmaier at sap.com>
Cc: Vladimir Kozlov <vladimir.kozlov at oracle.com>; jdk-updates-dev at openjdk.java.net; hotspot-compiler-dev at openjdk.java.net
Subject: Re: [11u] RFR 8245512: CRC32 optimization using AVX512 instructions

On 12/23/20 1:09 PM, Langer, Christoph wrote:
> 
> as we should be cautious about backports to an LTS release if something is not just a bugfix, I'm not sure whether this backport for a performance enhancement is good to go. Generally, if it can be proven that it's really just a potential performance improvement without side effects to other scenarios, I would be fine with it. But as I'm not an expert in this area, I'd prefer if it there was some further endorsement (or disapproval)...
> 
> @Andrew Haley; @Lindenmaier, Goetz; @Doerr, Martin, what's your assessment?

We could backport for a significant performance bottleneck, but I'm leaning toward the idea that JDK 11 is done: we're keeping it going by fixing bugs and adapting to changing environments, but that should be all.

However, there are exceptions to every rule!

There is a social problem in that maintainers get very demotivated because non-LTS releases are "never used" so people's work doesn't appear in production for years. I'm not sure exactly how to address that, except to say that using the OpenJDK release stream shouldn't be so very scary.

--
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com> https://keybase.io/andrewhaley
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