Thanks for the clarification ! From: Erik Joelsson [mailto:erik.joels...@oracle.com] Sent: Dienstag, 5. Juni 2018 17:51 To: Baesken, Matthias <matthias.baes...@sap.com>; 'hotspot-...@openjdk.java.net' <hotspot-...@openjdk.java.net>; 'build-dev@openjdk.java.net' <build-dev@openjdk.java.net> Cc: Zeller, Arno <arno.zel...@sap.com> Subject: Re: RFR: JDK-8202384: Introduce altserver jvm variant with
Hello Matthias, For GCC, you need 7.3.0 or later. For Microsoft you need VS2017 and I think some minimal update version (the option is called -Qspectre), we use 15.5.5. I was not involved in the benchmarking so I don't know any details there, only the conclusion. /Erik On 2018-06-05 01:30, Baesken, Matthias wrote: Hi Erik , is there some info available about the performance impact when disabling disabling speculative execution ? And which compiler versions are needed for this ? Best regards, Matthias >We need to add compilation flags for disabling speculative execution to >our native libraries and executables. In order to allow for users not >affected by problems with speculative execution to run a JVM at full >speed, we need to be able to ship two JVM libraries - one that is >compiled with speculative execution enabled, and one that is compiled >without. Note that this applies to the build time C++ flags, not the >compiler in the JVM itself. Luckily adding these flags to the rest of >the native libraries did not have a significant performance impact so >there is no need for making it optional there. > >This patch defines flags for disabling speculative execution for GCC and >Visual Studio and applies them to all binaries except libjvm when >available in the compiler. It defines a new jvm feature >no-speculative-cti, which is used to control whether to use the flags >for libjvm. It also defines a new jvm variant "altserver" which is the >same as server, but with this new feature added. > >For Oracle builds, we are changing the default for linux-x64 and >windows-x64 to build both server and altserver, giving the choice to the >user which JVM they want to use. If others would prefer this default, we >could make it default in configure as well. > >The change in GensrcJFR.gmk fixes a newly introduced race that appears >when building multiple jvm variants. > >Bug: https://bugs.openjdk.java.net/browse/JDK-8202384 > >Webrev: >http://cr.openjdk.java.net/~erikj/8202384/webrev.01<http://cr.openjdk.java.net/%7Eerikj/8202384/webrev.01>
