Boot JDK version; was Re: RFR: JDK-8188312 Use CDS if present when running the Boot JDK during build

Fri Oct 6 08:28:41 UTC 2017

Hello,

Indeed it does. I would say we should do it sooner rather than later. 
There are other issues coming up that relies on this switch as well so I 
will likely get a patch out in the near future.

/Erik

On 2017-10-05 18:15, Jonathan Gibbons wrote:
> This thread brings up the question ... when are we going to switch to 
> JDK 9 as the required boot JDK?  Is there any compelling reason to 
> -not- upgrade yet?
>
> -- Jon
>
>
> On 10/3/17 1:37 PM, Magnus Ihse Bursie wrote:
>> It might be the case that we should not really continue with this as 
>> long as we have JDK 8 as default boot jdk.
>>
>> If so, we should at least add a -Xshare:auto, which will allow the 
>> user to manually add a system-wide CDS archive to their boot jdk, and 
>> benefit from it.
>>
>> And then we'll revisit this when we switch to JDK 9, to see if 
>> "-XX:-VerifySharedSpaces -XX:SharedArchiveFile=x" is worth the effort.
>>
>> Sounds reasonable?
>>
>> /Magnus
>>
>>
>> On 2017-10-03 16:45, Erik Joelsson wrote:
>>> The change looks good, but unfortunately I don't see a lot of gain. 
>>> First of all it seems the -XX:SharedArchiveFile option removes a lot 
>>> of the performance gain. Here are some rough numbers from my 
>>> machine. All of them are "time make images" with a clean build 
>>> directory, on a 16 core/32 threads linux box. In some cases I did 
>>> two runs, which further shows the amount of variance in the build time.
>>>
>>> Baseline: boot jdk 8, no cds
>>> real    3m14.688s
>>> user    38m34.132s
>>> sys    5m4.032s
>>>
>>> real    3m11.086s
>>> user    38m16.820s
>>> sys    4m35.344s
>>>
>>> Magnus second patch: boot jdk 8, cds SharedArchiveFile
>>> real    3m6.268s
>>> user    38m9.168s
>>> sys    4m13.392s
>>>
>>> real    3m15.985s
>>> user    37m55.328s
>>> sys    3m50.140s
>>>
>>> Magnus first patch: boot jdk 8, cds in classes.jsa
>>> real    2m55.972s
>>> user    37m59.636s
>>> sys    4m1.020s
>>>
>>> Baseline with boot jdk 9, no cds
>>> real    3m14.262s
>>> user    40m9.216s
>>> sys    5m5.480s
>>>
>>> Magnus first patch: boot jdk 9, cds in classes.jsa
>>> real    3m12.721s
>>> user    39m29.332s
>>> sys    4m25.472s
>>>
>>> Magnus second patch: boot jdk 9, -XX:SharedArchiveFile, 
>>> -XX:-VerifySharedSpaces
>>> real    3m4.297s
>>> user    39m24.556s
>>> sys    4m31.980s
>>>
>>> So from this (certainly limited) data set, the only configuration 
>>> that shows meaningful improvement is with boot jdk 8 and the first 
>>> patch, where we stealth add classes.jsa to the boot jdk. I find this 
>>> a very bad thing to do in principle so would vote against such a 
>>> solution anyway. Also note that we will switch default boot from 8 
>>> to 9 very soon, so it's really the results on 9 that are relevant 
>>> here. In 9, there is another option, -XX:-VerifySharedSpaces which 
>>> removes most of the overhead added by -XX:SharedArchiveFile. Perhaps 
>>> using that this becomes worth while.
>>>
>>> I would like to see more data showing the optimization is actually 
>>> relevant. On my machine it seems to make a measurable difference, 
>>> but not a very significant one.
>>>
>>> One note on the proposed change. While working on this, when I 
>>> changed my boot jdk, configure did not regenerate the classes.jsa 
>>> file. I believe for safety we should regenerate on every configure 
>>> run. It's not that expensive anyway.
>>>
>>> /Erik
>>>
>>>
>>> On 2017-10-03 14:55, David Holmes wrote:
>>>> Looks good to me.
>>>>
>>>> Thanks,
>>>> David
>>>>
>>>> On 3/10/2017 10:47 PM, Magnus Ihse Bursie wrote:
>>>>> On 2017-10-03 14:21, David Holmes wrote:
>>>>>> Erik J. raises a good point in the bug report that 
>>>>>> -XX:SharedArchiveFile=xxx should be used if we create the 
>>>>>> archive. The build system has no business creating an archive 
>>>>>> inside the boot JDK.
>>>>>
>>>>> Agree, that is a better solution. I was not aware of the 
>>>>> -XX:SharedArchiveFile option.
>>>>>
>>>>> Here's an updated webrev:
>>>>> http://cr.openjdk.java.net/~ihse/JDK-8188312-use-CDS-for-bootjdk/webrev.02 
>>>>>
>>>>>
>>>>> I create the jsa file in configure-support, that way it can 
>>>>> survive a "make clean".
>>>>>
>>>>> /Magnus
>>>>>
>>>>>>
>>>>>> David
>>>>>>
>>>>>> On 3/10/2017 9:02 PM, David Holmes wrote:
>>>>>>> Hi Claes,
>>>>>>>
>>>>>>> On 3/10/2017 8:48 PM, Claes Redestad wrote:
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> -Xshare:auto silently ignores failures to map the shared 
>>>>>>>> archive and should be safe to use. I think you're thinking of 
>>>>>>>> -Xshare:on which will fail/abort the VM if mapping fails.
>>>>>>>
>>>>>>> Ah okay.
>>>>>>>
>>>>>>> In that case seems reasonable. But please test thoroughly across 
>>>>>>> all platforms in JPRT.
>>>>>>>
>>>>>>> Thanks,
>>>>>>> David
>>>>>>>
>>>>>>>> /Claes
>>>>>>>>
>>>>>>>>
>>>>>>>> On 2017-10-03 12:28, David Holmes wrote:
>>>>>>>>> Hi Magnus,
>>>>>>>>>
>>>>>>>>> As I just put in the bug report, it isn't quite this simple. 
>>>>>>>>> You have to be able to tolerate/recover from failure to map 
>>>>>>>>> the shared archive.
>>>>>>>>>
>>>>>>>>> Cheers,
>>>>>>>>> David
>>>>>>>>>
>>>>>>>>> On 3/10/2017 8:24 PM, Magnus Ihse Bursie wrote:
>>>>>>>>>> We should use CDS to minimize Java startup time during build. 
>>>>>>>>>> We run multiple Java commands, and every second counts.
>>>>>>>>>>
>>>>>>>>>> On my machine, I get a ~3% build time speedup with this fix.
>>>>>>>>>>
>>>>>>>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8188312
>>>>>>>>>> WebRev: 
>>>>>>>>>> http://cr.openjdk.java.net/~ihse/JDK-8188312-use-CDS-for-bootjdk/webrev.01 
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> /Magnus
>>>>>>>>
>>>>>
>>>
>>
>