Fwd: Webrev of Oracle ARM & AARCH64 Sources

Bob Vandette bob.vandette at oracle.com
Fri Sep 30 20:14:42 UTC 2016


I realize that we don’t officially support G1GC for ARM but here’s a crash running
the test harness using G1GC on a 32-bit ARM server VM in case anyone has
any insights.

Bob.


> Begin forwarded message:
> 
> From: Bob Vandette <bob.vandette at oracle.com>
> Subject: Re: Webrev of Oracle ARM & AARCH64 Sources
> Date: September 30, 2016 at 9:58:55 AM EDT
> To: David Holmes <David.Holmes at oracle.com>
> Cc: edward.nevill at gmail.com, aarch32-port-dev at openjdk.java.net, "hotspot-dev at openjdk.java.net developers" <hotspot-dev at openjdk.java.net>, aarch64-port-dev at openjdk.java.net
> 
> 
>> On Sep 30, 2016, at 7:23 AM, David Holmes <David.Holmes at oracle.com> wrote:
>> 
>> Hi Ed,
>> 
>> On 30/09/2016 8:32 PM, Edward Nevill wrote:
>>> Hi Bob,
>>> 
>>> On Wed, 2016-09-28 at 10:07 -0400, Bob Vandette wrote:
>>>> I’m am please to announce that I have completed our internal reviews and can now
>>>> open up the sources to our ARM 32 & 64 bit implementations of JDK9.
>>> 
>>> Great news.
>>> 
>>>> 
>>>> Here is a webrev that includes a patch that can be applied on top of the
>>>> (http://hg.openjdk.java.net/aarch32-port/jdk9-arm3264/ ) forest.
>>>> 
>>>>    http://cr.openjdk.java.net/~bobv/arm3264/webrev <http://cr.openjdk.java.net/~bobv/arm3264/webrev>
>>> 
>>> I have built this natively on armv7 and aarch64 without problems. In both cases I built the minimal,client,server combination.
>>> 
>>> I have also tested the server build with JTreg hotspot & langtools.
>>> 
>>> On aarch64 I got the following results:-
>>> 
>>> hotspot: Test results: passed: 1,280; failed: 8; error: 43
>>> langtools: Test results: passed: 3,700; failed: 1; error: 29
>>> 
>>> This is fairly typical, for example, using the Linaro 1609 build I get
>>> 
>>> hotspot: Test results: passed: 1,271; failed: 17; error: 43
>>> langtools: Test results: passed: 3,715; failed: 3; error: 12
>> 
>> So most of the "errors" are probably tests that are ignored.
>> 
>>> On armv7 I first of all had to pin the jvm.cfg to use -server as it kept on using the client as I was not running on a 'server class machine' (since my armv7 device is a Samsung Chromebook this is fair enough).
>>> 
>>> However, I then had problems with the test harness crashing with the error
>>> 
>>> #  Internal Error (synchronizer.cpp:1576), pid=6533, tid=6542
>>> #  guarantee(mid->header()->is_neutral()) failed: invariant
>>> 
>>> (hs_err here http://cr.openjdk.java.net/~enevill/aarch32/hs_err_pid6533.log)
>> 
>> Strange - that looks like our closed bug:
>> 
>> https://bugs.openjdk.java.net/browse/JDK-8071540
>> 
>> which should be fixed. It was a missing memory barrier issue.
> 
> I checked and this fix was applied but later a newer implementation
> was added.  The memory barriers were moved to cas_for_lock_acquire
> with optimized versions for aarch64.
> 
> Be aware that G1 support on 32-bit ARM is not fully supported by the GC team.
> It’s experimental.  This means that there was an attempt to implement it but it
> has not undergone the same level of testing as other platforms.  I’ll forward this
> issue to the GC team.
> 
> Bob.
> 
> 
>> 
>> Aside: we're going to have to figure out how to deal with currently closed bug reports.
>> 
>> David
>> -----
>> 
>>> On a subsequent run the test harness locked up after 85 tests.
>>> 
>>> It looks like there might be a problem with locks breaking with G1GC. I will keep investigating.
>>> 
>>> I ran it again using the template interpreter for the test harness and the server for the jdk under test and it ran successfully.
>>> 
>>> On armv7 I got
>>> 
>>> hotspot: Test results: passed: 1,202; failed: 11; error: 36
>>> langtools: Test results: passed: 3,718; failed: 5; error: 8
>>> 
>>> I also did some limited benchmarking which I am not going to share on a public forum. Lets just say the performance of the server JIT on armv7 was pleasing.
>>> 
>>> Thanks for all your work getting to this stage. It looks good to push and you should shortly have committeer rights, if you don't get them within a few days ping me and I will give ops a nudge.
>>> 
>>> All the best,
>>> Ed.
>>> 
>>> 
> 

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