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List: openjdk-serviceability-dev
Subject: RE: serviceability agent : problems when using gcc LTO (link time optimization)
From: "Baesken, Matthias" <matthias.baesken () sap ! com>
Date: 2020-01-15 16:11:03
Message-ID: AM6PR02MB4200A3D1523DB8800DCC194893370 () AM6PR02MB4200 ! eurprd02 ! prod ! outlook ! com
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Hello, here is another comparison for the larger JDK shared libs, this time \
with the sizes of build with linktime-gc (--gc-sections) added . ( just for the \
larger libs ) ( I had not enabled linktime-gc for libjvm in our test build , \
just for the JDK libs . )
Linuxx86_64 / gcc7
normal / with -flto / with linktime-gc (--gc-sections)
-----------------------------------------------------------
752K / 760K / 752K ./lib/libawt.so <------------------ this one gets a \
bit larger but only with flto 472K / 456K / 468K ./lib/libawt_xawt.so \
<------------------ small gain 1.5M / 824K / 900K ./lib/libfontmanager.so \
<------------------ HUGE gain , not as good with ltgc but still good 784K / 792K / \
784K ./lib/libfreetype.so <------------------ this one gets a bit larger \
(but not with ltgc) 260K / 244K / 252K ./lib/libjavajpeg.so \
<----------------- small gain 196K / 188K / 196K ./lib/libjava.so
280K / 256K / 276K ./lib/libjdwp.so <----------------- small gain
144K / 140K / 136K ./lib/libjimage.so
564K / 420K / 404K ./lib/liblcms.so <----------------- large gain , \
even better with ltgc 576K / 496K / 556K ./lib/libmlib_image.so \
<----------------- large gain with flto , small one with ltgc 368K / 212K / 236K \
./lib/libsplashscreen.so <----------------- large gain 320K / 296K / 300K \
./lib/libsunec.so <----------------- medium gain 23M / 17M / --not \
enabled--- ./lib/server/libjvm.so <----------------- big gain maybe because \
it is C++ ?
So one can see, that flto is usually a bit better than link-time-gc when it \
comes to improving lib sizes, but not always . However linktime-gc seems to be \
faster when comparing build times , I did not really notice much build time \
slowdown because of it . ( we have it enabled for linux s390x for some time in \
OpenJDK ). The linktime-gc also offers a nice feature to print out the eliminated \
stuff , that can be used to remove unused code cross-platform . e.g. the removed \
symbols from https://bugs.openjdk.java.net/browse/JDK-8234629 has been found \
this way .
Best regards, Matthias
Aleksei, Matthias,
thanks for the numbers. The size reduction on libjvm.so looks not bad, indeed.
Do you know if newer versions of GCC use the gold linker by default? I remember from \
some experiments which I did many years ago that gold was considerably faster \
compared to the default ld linker.
Unfortunately, the documentation I found about LTO/ld/gold [1,2] seems to be quite \
old and not very precise. Do you have gained any experience with LTO/gold and know if \
gold could maybe improve linking times with LTO?
[1] https://gcc.gnu.org/wiki/LinkTimeOptimization
[2] https://stackoverflow.com/questions/31688069/requirements-to-use-flto
Baesken, Matthias <matthias.baesken@sap.com<mailto:matthias.baesken@sap.com>> schrieb \
am Mi., 15. Jan. 2020, 07:02: Hello , I can comment on the code size . This is \
what I get when comparing a build without and with -flto .
gcc7 linux x86_64 product build, normal / with -flto
----------------------------------------------------------------------------------
du -sh on the *.so files gives :
16K / 16K ./lib/libattach.so
48K / 44K ./lib/libawt_headless.so
752K / 760K ./lib/libawt.so <------------------ this one gets a bit \
larger with flto 472K / 456K ./lib/libawt_xawt.so <------------------ small \
gain 36K / 32K ./lib/libdt_socket.so
16K /16K ./lib/libextnet.so
1.5M / 824K ./lib/libfontmanager.so <------------------ HUGE gain
784K / 792K ./lib/libfreetype.so <------------------ this one gets a bit \
larger with flto 56K / 56K ./lib/libinstrument.so
52K / 52K ./lib/libj2gss.so
20K / 20K ./lib/libj2pcsc.so
92K / 84K ./lib/libj2pkcs11.so
12K / 12k ./lib/libjaas.so
260K / 244K ./lib/libjavajpeg.so <----------------- small gain
196K / 188K ./lib/libjava.so
12K / 12K ./lib/libjawt.so
280K / 256K ./lib/libjdwp.so <----------------- small gain
144K / 140K ./lib/libjimage.so
84K / 76K ./lib/libjli.so
16K / 16K ./lib/libjsig.so
88K / 80K ./lib/libjsound.so
564K / 420K ./lib/liblcms.so <----------------- large gain
12K / 12K ./lib/libmanagement_agent.so
40K / 36K ./lib/libmanagement_ext.so
36K / 32K ./lib/libmanagement.so
576K / 496K ./lib/libmlib_image.so <----------------- large gain
112K / 108K ./lib/libnet.so
100K / 100K ./lib/libnio.so
16K / 16K ./lib/libprefs.so
8.0K / 8.0K ./lib/librmi.so
60K / 60K ./lib/libsaproc.so
36K / 32K ./lib/libsctp.so
368K / 212K ./lib/libsplashscreen.so <----------------- large gain
320K / 296K ./lib/libsunec.so <----------------- medium gain
72K / 72K ./lib/libverify.so
44K / 44K ./lib/libzip.so
16K / 16K ./lib/server/libjsig.so
23M / 17M ./lib/server/libjvm.so <----------------- big gain maybe \
because it is C++ ?
So for some libs you see 10% and more , but not for all . But most large \
libs like libjvm.so, libfontmanager.so or liblcms.so we see good \
results regarding reduced code size.
I Cannot say much about performance improvements , probably it would be small .
For SPEC you find something at
http://hubicka.blogspot.com/2019/05/gcc-9-link-time-and-inter-procedural.html
(not that these results would say too much about JVM performance ).
Best regards, Matthias
From: Volker Simonis <volker.simonis@gmail.com<mailto:volker.simonis@gmail.com>>
Sent: Mittwoch, 15. Januar 2020 14:40
To: Aleksei Voitylov \
<aleksei.voitylov@bell-sw.com<mailto:aleksei.voitylov@bell-sw.com>>
Cc: Baesken, Matthias <matthias.baesken@sap.com<mailto:matthias.baesken@sap.com>>; \
Magnus Ihse Bursie <magnus.ihse.bursie@oracle.com<mailto:magnus.ihse.bursie@oracle.com>>; \
serviceability-dev@openjdk.java.net<mailto:serviceability-dev@openjdk.java.net>; \
build-dev <build-dev@openjdk.java.net<mailto:build-dev@openjdk.java.net>>; \
hotspot-dev@openjdk.java.net<mailto:hotspot-dev@openjdk.java.net>
Subject: Re: serviceability agent : problems when using gcc LTO (link time \
optimization)
While we are speaking about all the drawbacks of LTO, it's still not clear what the \
benefits are? In the very first mail Matthias mentioned that there might be \
performance improvements but that performance is not the main driving factor behind \
this initiative. So is it the reduced code size (Matthias mentioned something around \
~10%)?
It would be nice to see some real numbers on various platform for both, the \
performance improvements for native parts like JIT/GC as well as for the size \
reduction. Aleksei Voitylov \
<aleksei.voitylov@bell-sw.com<mailto:aleksei.voitylov@bell-sw.com>> schrieb am Di., \
14. Jan. 2020, 09:54:
On 14/01/2020 19:57, Baesken, Matthias wrote:
> Hello Magnus and Aleksei, thanks for the input .
>
> The times you provided really look like they make a big difference at least for \
> people often building minimal-vm . Guess I have to measure myself a bit \
> (maybe the difference is not that big on our linux s390x / ppc64(le) ) .
> > If the change to enable lto by default is proposed, what would be the
> > recommended strategy for development?
> >
> Probably we should a) do not enable it by default but just make sure it can be \
> enabled easily and works for the minimal-vm
That would be welcome. I have high hopes to LTO the VM some time by
default, and the tendency observed is that the compiler time overhead
for GCC becomes smaller. At the same time there is no reason why vendors
that invested in testing and can absorb the build time hit could provide
binaries with LTO built VMs by passing an additional option flag.
> or b) take it easy to disable it for local development.
>
> Best regards, Matthias
>
>
>
> > Magnus, Matthias,
> >
> > for me, lto is a little heavyweight for development. x86_64 build time
> > with gcc 7:
> >
> > Server 1m32.484s
> > Server+Minimal 1m42.166s
> > Server+Minimal (--with-jvm-features="link-time-opt") 5m29.422s
> >
> > If the change to enable lto by default is proposed, what would be the
> > recommended strategy for development?
> >
> > For ARM32 Minimal, please keep in mind that it's not uncommon to disable
> > LTO plugin in commodity ARM32 gcc compiler distributions, so for some it
> > does not matter what settings we have in OpenJDK. I believe there could
> > be other reasons for that on top of build time (bugs?).
> >
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<p class="MsoNormal"><span lang="EN-US" \
style="mso-fareast-language:EN-US">Hello, here is another \
comparison for the larger JDK shared libs, this time with the \
sizes of build with linktime-gc (--gc-sections) added \
.<o:p></o:p></span></p> <p class="MsoNormal"><span lang="EN-US" \
style="mso-fareast-language:EN-US">( just for the larger libs )<o:p></o:p></span></p> \
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">( I \
had not enabled linktime-gc for libjvm in our \
test build , just for the JDK libs . )<o:p></o:p></span></p> <p \
class="MsoNormal"><span lang="EN-US" \
style="mso-fareast-language:EN-US"><o:p> </o:p></span></p> <p \
class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">Linuxx86_64 / \
gcc7<o:p></o:p></span></p> <p class="MsoNormal"><span lang="EN-US" \
style="mso-fareast-language:EN-US"><o:p> </o:p></span></p> <p \
class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">normal / with \
-flto / with linktime-gc (--gc-sections)<o:p></o:p></span></p> <p \
class="MsoNormal"><span lang="EN-US" \
style="mso-fareast-language:EN-US">-----------------------------------------------------------<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">752K / \
760K / 752K \
./lib/libawt.so \
<------------------ this one gets a bit larger but only with \
flto<o:p></o:p></span></p> <p class="MsoNormal"><span lang="EN-US" \
style="mso-fareast-language:EN-US">472K / 456K / 468K \
./lib/libawt_xawt.so <------------------ small \
gain<o:p></o:p></span></p> <p class="MsoNormal"><span lang="EN-US" \
style="mso-fareast-language:EN-US">1.5M / 824K / 900K \
./lib/libfontmanager.so <------------------ HUGE \
gain , not as good with ltgc but still good<o:p></o:p></span></p> <p \
class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">784K / 792K / \
784K ./lib/libfreetype.so \
<------------------ this one gets a bit larger (but not with \
ltgc)<o:p></o:p></span></p> <p class="MsoNormal"><span lang="EN-US" \
style="mso-fareast-language:EN-US">260K / 244K / 252K \
./lib/libjavajpeg.so \
<----------------- small \
gain<o:p></o:p></span></p> <p class="MsoNormal"><span lang="EN-US" \
style="mso-fareast-language:EN-US">196K / 188K / 196K \
./lib/libjava.so<o:p></o:p></span></p> <p class="MsoNormal"><span lang="EN-US" \
style="mso-fareast-language:EN-US">280K / 256K / 276K \
./lib/libjdwp.so \
<----------------- small gain<o:p></o:p></span></p> <p class="MsoNormal"><span \
lang="EN-US" style="mso-fareast-language:EN-US">144K / 140K / 136K \
./lib/libjimage.so<o:p></o:p></span></p> <p class="MsoNormal"><span lang="EN-US" \
style="mso-fareast-language:EN-US">564K / 420K / 404K \
./lib/liblcms.so \
<----------------- large gain , even better with ltgc \
<o:p></o:p></span></p> <p class="MsoNormal"><span lang="EN-US" \
style="mso-fareast-language:EN-US">576K / 496K / 556K \
./lib/libmlib_image.so <----------------- \
large gain with flto , small one with ltgc<o:p></o:p></span></p> <p \
class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">368K / 212K / \
236K ./lib/libsplashscreen.so \
<----------------- large gain<o:p></o:p></span></p> <p class="MsoNormal"><span \
lang="EN-US" style="mso-fareast-language:EN-US">320K / 296K / 300K \
./lib/libsunec.so \
<----------------- medium gain<o:p></o:p></span></p> <p class="MsoNormal"><span \
lang="EN-US" style="mso-fareast-language:EN-US">23M / 17M / --not \
enabled--- \
./lib/server/libjvm.so \
<----------------- big gain maybe because it is C++ \
?<o:p></o:p></span></p> <p class="MsoNormal"><span lang="EN-US" \
style="mso-fareast-language:EN-US"><o:p> </o:p></span></p> <p \
class="MsoNormal"><span lang="EN-US" \
style="mso-fareast-language:EN-US"><o:p> </o:p></span></p> <p \
class="MsoNormal"><span lang="EN-US" \
style="mso-fareast-language:EN-US">So one can see, that \
flto is usually a bit better than link-time-gc when it \
comes to improving lib sizes, but not always .<o:p></o:p></span></p> <p \
class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">However \
linktime-gc seems to be faster when comparing build times , I \
did not really notice much build time slowdown because of it \
.<o:p></o:p></span></p> <p class="MsoNormal"><span lang="EN-US" \
style="mso-fareast-language:EN-US">( we have it enabled for linux \
s390x for some time in OpenJDK ).<o:p></o:p></span></p> <p \
class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">The \
linktime-gc also offers a nice feature to print out the eliminated \
stuff , that can be used to remove unused code cross-platform \
.<o:p></o:p></span></p> <p class="MsoNormal"><span lang="EN-US" \
style="mso-fareast-language:EN-US">e.g. the removed symbols from \
</span><a href="https://bugs.openjdk.java.net/browse/JDK-8234629"><span \
lang="EN-US">https://bugs.openjdk.java.net/browse/JDK-8234629</span></a><span \
lang="EN-US"> has been found this way .</span><span lang="EN-US" \
style="mso-fareast-language:EN-US"><o:p></o:p></span></p> <p class="MsoNormal"><span \
lang="EN-US" style="mso-fareast-language:EN-US"><o:p> </o:p></span></p> <p \
class="MsoNormal"><span lang="EN-US" \
style="mso-fareast-language:EN-US"><o:p> </o:p></span></p> <p \
class="MsoNormal"><span lang="EN-US" style="mso-fareast-language:EN-US">Best regards, \
Matthias<o:p></o:p></span></p> <p class="MsoNormal"><span lang="EN-US" \
style="mso-fareast-language:EN-US"><o:p> </o:p></span></p> <p \
class="MsoNormal"><span lang="EN-US" \
style="mso-fareast-language:EN-US"><o:p> </o:p></span></p> <div \
style="border:none;border-left:solid blue 1.5pt;padding:0cm 0cm 0cm 4.0pt"> <p \
class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p> <div>
<p class="MsoNormal"><span lang="EN-US">Aleksei, Matthias,<o:p></o:p></span></p>
<div>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal">thanks for the numbers. The size reduction on libjvm.so looks \
not bad, indeed.<o:p></o:p></p> </div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">Do you know if newer versions of GCC use the gold linker by \
default? I remember from some experiments which I did many years ago that gold was \
considerably faster compared to the default ld linker.<o:p></o:p></p> </div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">Unfortunately, the documentation I found about LTO/ld/gold [1,2] \
seems to be quite old and not very precise. Do you have gained any experience with \
LTO/gold and know if gold could maybe improve linking times with LTO?<o:p></o:p></p> \
</div> <div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">[1] <a \
href="https://gcc.gnu.org/wiki/LinkTimeOptimization">https://gcc.gnu.org/wiki/LinkTimeOptimization</a><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">[2] <a \
href="https://stackoverflow.com/questions/31688069/requirements-to-use-flto">https://stackoverflow.com/questions/31688069/requirements-to-use-flto</a><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div>
<p class="MsoNormal">Baesken, Matthias <<a \
href="mailto:matthias.baesken@sap.com">matthias.baesken@sap.com</a>> schrieb am \
Mi., 15. Jan. 2020, 07:02:<o:p></o:p></p> </div>
<blockquote style="border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm \
6.0pt;margin-left:4.8pt;margin-right:0cm"> <div>
<div>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US">Hello , I can comment on the code size . This is \
what I get when comparing a build without and with \
-flto .</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US"> </span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">gcc7 \
linux x86_64 product build, normal / with -flto</span><o:p></o:p></p> <p \
class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US">----------------------------------------------------------------------------------</span><o:p></o:p></p>
<p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US"> </span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">du -sh \
on the *.so files gives :</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US"> </span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">16K / \
16K ./lib/libattach.so</span><o:p></o:p></p> <p \
class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US">48K / 44K \
./lib/libawt_headless.so</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">752K / \
760K \
./lib/libawt.so \
<------------------ this one gets a bit larger with flto</span><o:p></o:p></p> <p \
class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US">472K / 456K \
./lib/libawt_xawt.so <------------------ small \
gain</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">36K / \
32K ./lib/libdt_socket.so</span><o:p></o:p></p> <p \
class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US">16K /16K \
./lib/libextnet.so</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">1.5M / \
824K ./lib/libfontmanager.so \
<------------------ HUGE gain</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">784K / \
792K ./lib/libfreetype.so \
<------------------ this one gets a bit larger with flto</span><o:p></o:p></p> <p \
class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US">56K / 56K \
./lib/libinstrument.so</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">52K / \
52K ./lib/libj2gss.so</span><o:p></o:p></p> <p \
class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US">20K / 20K \
./lib/libj2pcsc.so</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">92K / \
84K ./lib/libj2pkcs11.so</span><o:p></o:p></p> <p \
class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US">12K / 12k \
./lib/libjaas.so</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">260K / \
244K \
./lib/libjavajpeg.so \
<----------------- small gain</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">196K / \
188K ./lib/libjava.so</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">12K / \
12K ./lib/libjawt.so</span><o:p></o:p></p> <p \
class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US">280K / 256K \
./lib/libjdwp.so \
<----------------- small gain</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">144K / \
140K ./lib/libjimage.so</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">84K / \
76K ./lib/libjli.so</span><o:p></o:p></p> <p \
class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US">16K / 16K \
./lib/libjsig.so</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">88K / \
80K ./lib/libjsound.so</span><o:p></o:p></p> <p \
class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US">564K / 420K \
./lib/liblcms.so \
<----------------- large gain</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">12K / \
12K ./lib/libmanagement_agent.so</span><o:p></o:p></p> \
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US">40K / 36K \
./lib/libmanagement_ext.so</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">36K / \
32K ./lib/libmanagement.so</span><o:p></o:p></p> <p \
class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US">576K / 496K \
./lib/libmlib_image.so <----------------- \
large gain</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">112K / \
108K ./lib/libnet.so</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">100K / \
100K ./lib/libnio.so</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US">16K / 16K \
./lib/libprefs.so</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">8.0K / \
8.0K ./lib/librmi.so</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">60K / \
60K ./lib/libsaproc.so</span><o:p></o:p></p> <p \
class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US">36K / 32K \
./lib/libsctp.so</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">368K / \
212K ./lib/libsplashscreen.so \
<----------------- large gain</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">320K / \
296K \
./lib/libsunec.so \
<----------------- medium gain</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">72K / \
72K ./lib/libverify.so</span><o:p></o:p></p> <p \
class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US">44K / 44K \
./lib/libzip.so</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">16K / \
16K ./lib/server/libjsig.so</span><o:p></o:p></p> <p \
class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US">23M / 17M \
./lib/server/libjvm.so \
<----------------- big gain maybe because it is C++ \
?</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US"> </span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US"> </span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US">So for some libs you see 10% and more , but not \
for all . But most large libs like \
libjvm.so, libfontmanager.so or \
liblcms.so we see good results regarding reduced code \
size.</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US"> </span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">I \
Cannot say much about performance improvements , probably it would be small \
.</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US"> </span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">For \
SPEC you find something at </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US"> </span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><a \
href="http://hubicka.blogspot.com/2019/05/gcc-9-link-time-and-inter-procedural.html" \
target="_blank"><span \
lang="EN-US">http://hubicka.blogspot.com/2019/05/gcc-9-link-time-and-inter-procedural.html</span></a><o:p></o:p></p>
<p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US"> </span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">(not \
that these results would say too much about JVM performance \
).</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US"> </span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US"> </span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US">Best \
regards, Matthias</span><o:p></o:p></p> <p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span \
lang="EN-US"> </span><o:p></o:p></p> <div style="border:none;border-left:solid \
blue 1.5pt;padding:0cm 0cm 0cm 4.0pt"> <div>
<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span \
lang="EN-US">From:</span></b><span lang="EN-US"> Volker Simonis <<a \
href="mailto:volker.simonis@gmail.com" \
target="_blank">volker.simonis@gmail.com</a>> <br>
<b>Sent:</b> Mittwoch, 15. Januar 2020 14:40<br>
<b>To:</b> Aleksei Voitylov <<a href="mailto:aleksei.voitylov@bell-sw.com" \
target="_blank">aleksei.voitylov@bell-sw.com</a>><br> <b>Cc:</b> Baesken, Matthias \
<<a href="mailto:matthias.baesken@sap.com" \
target="_blank">matthias.baesken@sap.com</a>>; Magnus Ihse Bursie <<a \
href="mailto:magnus.ihse.bursie@oracle.com" \
target="_blank">magnus.ihse.bursie@oracle.com</a>>; <a \
href="mailto:serviceability-dev@openjdk.java.net" \
target="_blank">serviceability-dev@openjdk.java.net</a>; build-dev <<a \
href="mailto:build-dev@openjdk.java.net" \
target="_blank">build-dev@openjdk.java.net</a>>; <a \
href="mailto:hotspot-dev@openjdk.java.net" \
target="_blank">hotspot-dev@openjdk.java.net</a><br> <b>Subject:</b> Re: \
serviceability agent : problems when using gcc LTO (link time \
optimization)</span><o:p></o:p></p> </div>
</div>
<p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p> \
<div> <div>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">While \
we are speaking about all the drawbacks of LTO, it's still not clear what the \
benefits are? In the very first mail Matthias mentioned that there might be \
performance improvements but that performance is not the main driving factor behind \
this initiative. So is it the reduced code size (Matthias mentioned something around \
~10%)?<o:p></o:p></p> </div>
<div>
<p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p> \
</div> <div>
<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:12.0pt">It would be \
nice to see some real numbers on various platform for both, the performance \
improvements for native parts like JIT/GC as well as for the size \
reduction.<o:p></o:p></p> <div>
<div>
<p class="MsoNormal" \
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Aleksei Voitylov <<a \
href="mailto:aleksei.voitylov@bell-sw.com" \
target="_blank">aleksei.voitylov@bell-sw.com</a>> schrieb am Di., 14. Jan. 2020, \
09:54:<o:p></o:p></p> </div>
<blockquote style="border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm \
6.0pt;margin-left:4.8pt;margin-top:5.0pt;margin-right:0cm;margin-bottom:5.0pt"> <p \
class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:12.0pt"><br> On \
14/01/2020 19:57, Baesken, Matthias wrote:<br> > Hello Magnus and \
Aleksei, thanks for the input .<br> ><br>
> The times you provided really look like they make a big difference \
at least for people often building minimal-vm .<br> \
> Guess I have to measure myself a bit (maybe the difference is not that big \
on our linux s390x / ppc64(le) ) .<br> ><br>
>> If the change to enable lto by default is proposed, what would be the<br>
>> recommended strategy for development?<br>
>><br>
> Probably we should a) do not enable it by default but just \
make sure it can be enabled easily and works for the minimal-vm \
<br> That would be welcome. I have high hopes to LTO the VM some time by<br>
default, and the tendency observed is that the compiler time overhead<br>
for GCC becomes smaller. At the same time there is no reason why vendors<br>
that invested in testing and can absorb the build time hit could provide<br>
binaries with LTO built VMs by passing an additional option flag.<br>
> or b) take it easy to disable it for local \
development.<br> ><br>
> Best regards, Matthias<br>
><br>
><br>
><br>
>> Magnus, Matthias,<br>
>><br>
>> for me, lto is a little heavyweight for development. x86_64 build time<br>
>> with gcc 7:<br>
>><br>
>> Server 1m32.484s<br>
>> Server+Minimal 1m42.166s<br>
>> Server+Minimal (--with-jvm-features="link-time-opt") \
5m29.422s<br> >><br>
>> If the change to enable lto by default is proposed, what would be the<br>
>> recommended strategy for development?<br>
>><br>
>> For ARM32 Minimal, please keep in mind that it's not uncommon to disable<br>
>> LTO plugin in commodity ARM32 gcc compiler distributions, so for some it<br>
>> does not matter what settings we have in OpenJDK. I believe there could<br>
>> be other reasons for that on top of build time (bugs?).<br>
>><o:p></o:p></p>
</blockquote>
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