G1 Performance [Was: JEP 248: Make G1 the Default Garbage Collector]

[Vitaly Davidovich]

Yes, but that StoreLoad is effectively a full fence on at least x86.

sent from my phone
On Jul 30, 2015 3:49 AM, "Andrew Dinn" <adinn at redhat.com> wrote:

> On 29/07/15 19:27, Vitaly Davidovich wrote:
> > IIRC Erik's proposal involves TLB shootdowns, which I'm not sure will
> speed
> > this up.  A few months back there was a discussion around this in the
> > context of adding full fence with CMS when UseConditionalCardMarking is
> > enabled (which I'm not sure if that change went in actually) and
> > interaction with precleaning.
>
> A change did go in but not quite as you describe it. As a fix for
> JDK-8079315 a /StoreLoad/ barrier was added -- see this changeset:
>
>   http://hg.openjdk.java.net/jdk9/hs-rt/hotspot/rev/a7d15bf7b961
>
> I agree that TLB shootdowns are unlikely to improve performance -- also,
> they are a hostage to fortune since you are at the mercy of the OS
> implementation as regards both performance and, perhaps to a lesser
> degree, correctness.
> regards,
>
>
> Andrew Dinn
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>
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