RFR(M): 8204524: Unnecessary memory barriers in G1ParScanThreadState::copy_to_survivor_space

[Michihiro Horie]

Hi Derek,

Thank you for sharing your status of still having inconsistent results with
the patch. I would wait for your updates.

Thanks again,


Best regards,
--
Michihiro,
IBM Research - Tokyo



From:	"White, Derek" <Derek.White at cavium.com>
To:	Kim Barrett <kim.barrett at oracle.com>, Michihiro Horie
            <HORIE at jp.ibm.com>
Cc:	Gustavo Bueno Romero <gromero at br.ibm.com>,
            "david.holmes at oracle.com" <david.holmes at oracle.com>,
            "hotspot-gc-dev at openjdk.java.net"
            <hotspot-gc-dev at openjdk.java.net>
Date:	2018/06/15 17:55
Subject:	RE: RFR(M): 8204524: Unnecessary memory barriers in
            G1ParScanThreadState::copy_to_survivor_space



Hi Michihiro,

Status update:
My colleague and I are getting inconsistent results with this patch: -23%
to +7% on SPECjbb, so we're trying to verify what's going on.

On an unrelated note, the aarch64 port relies on GCC's
__atomic_compare_exchange to implemented the relaxed case of
Atomic::PlatformCmpxchg, and gcc 6 and earlier sometimes do a poor job on
it. Not enough to account for the numbers we saw though.

I hope to have an answer by Monday.

 - Derek

> -----Original Message-----
> From: hotspot-gc-dev [mailto:hotspot-gc-dev-bounces at openjdk.java.net]
> On Behalf Of Kim Barrett
> Sent: Wednesday, June 13, 2018 5:16 PM
> To: Michihiro Horie <HORIE at jp.ibm.com>
> Cc: Gustavo Bueno Romero <gromero at br.ibm.com>;
> david.holmes at oracle.com; hotspot-gc-dev at openjdk.java.net
> Subject: Re: RFR(M): 8204524: Unnecessary memory barriers in
> G1ParScanThreadState::copy_to_survivor_space
>
> External Email
>
> > On Jun 7, 2018, at 2:01 AM, Michihiro Horie <HORIE at jp.ibm.com> wrote:
> >
> > Dear all,
> >
> > Would you please review the following change?
> >
> > Bug:
https://bugs.openjdk.java.net/browse/JDK-8204524

> > Webrev:
http://cr.openjdk.java.net/~mhorie/8204524/webrev.00

>
> I was going to say that this looks good to me.
>
> But then I saw Derek White’s reply about an unexpected performance
> regression.
> I’d like to wait until he reports back.




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