Faster rebuild with GNU gold linker

[Ioi Lam]

Ahh, I was using a debug build of lld. After making a release build, the 
link time drops to 1.1 seconds! It's definitely better than gold.

On 2/19/19 10:35 PM, Ioi Lam wrote:
> Hi Martin,
>
> Thanks for the info. I didn't know that this has been discussed so 
> recently. Should have checked befor I posted.
>
> Anyway, I built the latest lld from GIT, but it's slower than gold on 
> my machine. Just linking libjvm.so is 5.8s vs 3.8s.
>
> On 2/19/19 5:23 PM, Martin Buchholz wrote:
>> https://openjdk.markmail.org/thread/q3layufiyjivu42c
>>
>> On Tue, Feb 19, 2019 at 5:03 PM Ioi Lam <ioi.lam at oracle.com 
>> <mailto:ioi.lam at oracle.com>> wrote:
>>
>>     For the impatient engineers ....
>>
>>     I did some measurement between the default GNU linker "ld" vs
>>     "ld.gold".
>>     I am trying to get the fastest rebuild time after I modify one cpp
>>     file.
>>     With gold, it's down to about 1/3 of the original time.
>>
>>
>>     slowdebug (~220MB libjvm.so)
>>
>>                       recompile 1 cpp file  |  relink libjvm.so only
>>     ld:                   33 s                   25 s
>>     gold 1 thread:        16 s                    9 s
>>     gold 8 threads:       13 s                    6 s
>>
>>
>>     fastdebug (~360MB libjvm.so)
>>
>>
>>                       recompile 1 cpp file  |  relink libjvm.so only
>>     ld:                   35 s                    25 s
>>     gold 1 thread:        18 s                    10 s
>>     gold 8 threads:       15 s                     6 s
>>
>>
>>     Question: do we want to add built-in support for gold into the JDK
>>     makefiles?
>>
>>
>>     Notes:
>>
>>     To choose gold, run configure with something like:
>>
>>          --with-extra-ldflags='-fuse-ld=gold
>>     -Wl,--threads,--thread-count,8'
>>
>>     I essentially do a "make hotspot" and then move the libjvm.so into
>>     a JDK
>>     image, instead of doing a full JDK image build.
>>
>>     "make hotspot" makes a copy of libjvm.so (from
>>     support/modules_libs/java.base/server/ to jdk/lib/server/). I
>>     hacked the
>>     Makefile to make a hard link instead to avoid the unnecessary I/O.
>>
>>     libjvm.so is built with --with-native-debug-symbols=internal to 
>> avoid
>>     the expensive invocations of objcopy and strip.
>>
>>
>>     My environment:
>>
>>     I am using gcc7.3.0 on Ubuntu 16.04.5 on a 5 year old Dell Precision
>>     T7600 with dual socket Xeon E5-2665 @ 2.40GHz, 64GB RAM, Samsung
>>     840 PRO
>>     SSD. I suspect gold can run even faster, but my slow SSD is
>>     holding it back.
>>
>>     ld version   = GNU ld (GNU Binutils) 2.30
>>     gold version = GNU gold (GNU Binutils for Ubuntu 2.26.1) 1.11
>>
>>     (These are just the versions available to me on my machine, not
>>     necessarily the best)
>>
>